Initial webgl renderer implementation

demo/client.ts

@@ -203,11 +203,11 @@ function initOptions(term: TerminalType): void {
     bellSound: null,
     bellStyle: ['none', 'sound'],
     cursorStyle: ['block', 'underline', 'bar'],
-    experimentalCharAtlas: ['none', 'static', 'dynamic'],
+    experimentalCharAtlas: ['none', 'static', 'dynamic', 'webgl'],
     fontFamily: null,
     fontWeight: ['normal', 'bold', '100', '200', '300', '400', '500', '600', '700', '800', '900'],
     fontWeightBold: ['normal', 'bold', '100', '200', '300', '400', '500', '600', '700', '800', '900'],
-    rendererType: ['dom', 'canvas'],
+    rendererType: ['dom', 'canvas', 'webgl'],
     experimentalBufferLineImpl: ['JsArray', 'TypedArray']
   };
   const options = Object.keys((<any>term)._core.options);
@@ -235,7 +235,7 @@ function initOptions(term: TerminalType): void {
   });
   html += '</div><div class="option-group">';
   numberOptions.forEach(o => {
-    html += `<div class="option"><label>${o} <input id="opt-${o}" type="number" value="${term.getOption(o)}"/></label></div>`;
+    html += `<div class="option"><label>${o} <input id="opt-${o}" type="number" value="${term.getOption(o)}" step="${o === 'lineHeight' ? '0.1' : '1'}"/></label></div>`;
   });
   html += '</div><div class="option-group">';
   Object.keys(stringOptions).forEach(o => {
@@ -265,7 +265,7 @@ function initOptions(term: TerminalType): void {
       if (o === 'cols' || o === 'rows') {
         updateTerminalSize();
       } else {
-        term.setOption(o, parseInt(input.value, 10));
+        term.setOption(o, o === 'lineHeight' ? parseFloat(input.value) : parseInt(input.value, 10));
       }
     });
   });

src/Terminal.ts

@@ -52,6 +52,7 @@ import { DomRenderer } from './renderer/dom/DomRenderer';
 import { IKeyboardEvent } from './common/Types';
 import { evaluateKeyboardEvent } from './core/input/Keyboard';
 import { KeyboardResultType, ICharset } from './core/Types';
+import { WebglRenderer } from './renderer/webgl/WebglRenderer';
 
 // Let it work inside Node.js for automated testing purposes.
 const document = (typeof window !== 'undefined') ? window.document : null;
@@ -462,6 +463,7 @@ export class Terminal extends EventEmitter implements ITerminal, IDisposable, II
           this.renderer.onResize(this.cols, this.rows);
           this.refresh(0, this.rows - 1);
         }
+        break;
       case 'rendererType':
         if (this.renderer) {
           this.unregister(this.renderer);
@@ -761,6 +763,7 @@ export class Terminal extends EventEmitter implements ITerminal, IDisposable, II
     switch (this.options.rendererType) {
       case 'canvas': this.renderer = new Renderer(this, this.options.theme); break;
       case 'dom': this.renderer = new DomRenderer(this, this.options.theme); break;
+      case 'webgl': this.renderer = new WebglRenderer(this, this.options.theme); break;
       default: throw new Error(`Unrecognized rendererType "${this.options.rendererType}"`);
     }
     this.register(this.renderer);

src/Types.ts

@@ -311,6 +311,7 @@ export interface IBufferSet extends IEventEmitter {
 
 export interface ISelectionManager {
   selectionText: string;
+  hasSelection: boolean;
   selectionStart: [number, number];
   selectionEnd: [number, number];
 

src/renderer/atlas/CharAtlasCache.ts

@@ -11,11 +11,13 @@ import BaseCharAtlas from './BaseCharAtlas';
 import DynamicCharAtlas from './DynamicCharAtlas';
 import NoneCharAtlas from './NoneCharAtlas';
 import StaticCharAtlas from './StaticCharAtlas';
+import WebglCharAtlas from '../webgl/WebglCharAtlas';
 
 const charAtlasImplementations = {
   'none': NoneCharAtlas,
   'static': StaticCharAtlas,
-  'dynamic': DynamicCharAtlas
+  'dynamic': DynamicCharAtlas,
+  'webgl': WebglCharAtlas
 };
 
 interface ICharAtlasCacheEntry {
@@ -38,9 +40,10 @@ export function acquireCharAtlas(
   terminal: ITerminal,
   colors: IColorSet,
   scaledCharWidth: number,
-  scaledCharHeight: number
+  scaledCharHeight: number,
+  devicePixelRatio?: number
 ): BaseCharAtlas {
-  const newConfig = generateConfig(scaledCharWidth, scaledCharHeight, terminal, colors);
+  const newConfig = generateConfig(scaledCharWidth, scaledCharHeight, terminal, colors, devicePixelRatio);
 
   // TODO: Currently if a terminal changes configs it will not free the entry reference (until it's disposed)
 
@@ -54,6 +57,7 @@ export function acquireCharAtlas(
       }
       // The configs differ, release the terminal from the entry
       if (entry.ownedBy.length === 1) {
+        entry.atlas.dispose();
         charAtlasCache.splice(i, 1);
       } else {
         entry.ownedBy.splice(ownedByIndex, 1);
@@ -94,6 +98,7 @@ export function removeTerminalFromCache(terminal: ITerminal): void {
     if (index !== -1) {
       if (charAtlasCache[i].ownedBy.length === 1) {
         // Remove the cache entry if it's the only terminal
+        charAtlasCache[i].atlas.dispose();
         charAtlasCache.splice(i, 1);
       } else {
         // Remove the reference from the cache entry

src/renderer/atlas/CharAtlasUtils.ts

@@ -7,7 +7,7 @@ import { ITerminal } from '../../Types';
 import { IColorSet } from '../Types';
 import { ICharAtlasConfig } from '../../shared/atlas/Types';
 
-export function generateConfig(scaledCharWidth: number, scaledCharHeight: number, terminal: ITerminal, colors: IColorSet): ICharAtlasConfig {
+export function generateConfig(scaledCharWidth: number, scaledCharHeight: number, terminal: ITerminal, colors: IColorSet, devicePixelRatio: number = window.devicePixelRatio): ICharAtlasConfig {
   // null out some fields that don't matter
   const clonedColors = <IColorSet>{
     foreground: colors.foreground,
@@ -21,7 +21,7 @@ export function generateConfig(scaledCharWidth: number, scaledCharHeight: number
   };
   return {
     type: terminal.options.experimentalCharAtlas,
-    devicePixelRatio: window.devicePixelRatio,
+    devicePixelRatio,
     scaledCharWidth,
     scaledCharHeight,
     fontFamily: terminal.options.fontFamily,

src/renderer/webgl/GlyphRenderer.ts

@@ -0,0 +1,343 @@
+/**
+ * Copyright (c) 2018 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { createProgram, PROJECTION_MATRIX } from './WebglUtils';
+import { IRenderDimensions } from '../Types';
+import { ITerminal, IBufferLine } from '../../Types';
+import { NULL_CELL_CODE, CHAR_DATA_CHAR_INDEX } from '../../Buffer';
+import WebglCharAtlas from './WebglCharAtlas';
+import { IWebGL2RenderingContext, IWebGLVertexArrayObject, IRenderModel, IRasterizedGlyph } from './Types';
+import { INDICIES_PER_CELL } from './WebglRenderer';
+import { COMBINED_CHAR_BIT_MASK } from './RenderModel';
+
+interface IVertices {
+  attributes: Float32Array;
+  selectionAttributes: Float32Array;
+  cellPosition: Float32Array;
+  count: number;
+}
+
+const enum VertexAttribLocations {
+  UNIT_QUAD = 0,
+  CELL_POSITION = 1,
+  OFFSET = 2,
+  SIZE = 3,
+  TEXCOORD = 4,
+  TEXSIZE = 5
+}
+
+const vertexShaderSource = `#version 300 es
+layout (location = ${VertexAttribLocations.UNIT_QUAD}) in vec2 a_unitquad;
+layout (location = ${VertexAttribLocations.CELL_POSITION}) in vec2 a_cellpos;
+layout (location = ${VertexAttribLocations.OFFSET}) in vec2 a_offset;
+layout (location = ${VertexAttribLocations.SIZE}) in vec2 a_size;
+layout (location = ${VertexAttribLocations.TEXCOORD}) in vec2 a_texcoord;
+layout (location = ${VertexAttribLocations.TEXSIZE}) in vec2 a_texsize;
+
+uniform mat4 u_projection;
+uniform vec2 u_resolution;
+
+out vec2 v_texcoord;
+
+void main() {
+  vec2 zeroToOne = (a_offset / u_resolution) + a_cellpos + (a_unitquad * a_size);
+  gl_Position = u_projection * vec4(zeroToOne, 0.0, 1.0);
+  v_texcoord = a_texcoord + a_unitquad * a_texsize;
+}`;
+
+const fragmentShaderSource = `#version 300 es
+precision mediump float;
+
+in vec2 v_texcoord;
+
+uniform sampler2D u_texture;
+
+out vec4 outColor;
+
+void main() {
+  outColor = texture(u_texture, v_texcoord);
+}`;
+
+const INDICES_PER_CELL = 8;
+const BYTES_PER_CELL = INDICES_PER_CELL * Float32Array.BYTES_PER_ELEMENT;
+
+export class GlyphRenderer {
+  private _atlas: WebglCharAtlas;
+
+  private _program: WebGLProgram;
+  private _vertexArrayObject: IWebGLVertexArrayObject;
+  private _projectionLocation: WebGLUniformLocation;
+  private _resolutionLocation: WebGLUniformLocation;
+  private _textureLocation: WebGLUniformLocation;
+  private _atlasTexture: WebGLTexture;
+  private _attributesBuffer: WebGLBuffer;
+  private _cellPositionBuffer: WebGLBuffer;
+
+  private _lineLengths: Int16Array = new Int16Array(0);
+  private _vertices: IVertices = {
+    count: 0,
+    attributes: new Float32Array(0),
+    selectionAttributes: new Float32Array(0),
+    cellPosition: new Float32Array(0)
+  };
+
+  constructor(
+    private _terminal: ITerminal,
+    private _gl: IWebGL2RenderingContext,
+    private _dimensions: IRenderDimensions
+  ) {
+    const gl = this._gl;
+
+    this._program = createProgram(gl, vertexShaderSource, fragmentShaderSource);
+
+    // Uniform locations
+    this._projectionLocation = gl.getUniformLocation(this._program, 'u_projection');
+    this._resolutionLocation = gl.getUniformLocation(this._program, 'u_resolution');
+    this._textureLocation = gl.getUniformLocation(this._program, 'u_texture');
+
+    // Create and set the vertex array object
+    this._vertexArrayObject = gl.createVertexArray();
+    gl.bindVertexArray(this._vertexArrayObject);
+
+    // Setup a_unitquad, this defines the 4 vertices of a rectangle
+    const unitQuadVertices = new Float32Array([0, 0, 1, 0, 0, 1, 1, 1]);
+    const unitQuadVerticesBuffer = gl.createBuffer();
+    gl.bindBuffer(gl.ARRAY_BUFFER, unitQuadVerticesBuffer);
+    gl.bufferData(gl.ARRAY_BUFFER, unitQuadVertices, gl.STATIC_DRAW);
+    gl.enableVertexAttribArray(VertexAttribLocations.UNIT_QUAD);
+    gl.vertexAttribPointer(VertexAttribLocations.UNIT_QUAD, 2, this._gl.FLOAT, false, 0, 0);
+
+    // Setup the unit quad element array buffer, this points to indices in
+    // unitQuadVertuces to allow is to draw 2 triangles from the vertices
+    const unitQuadElementIndices = new Uint8Array([0, 1, 3, 0, 2, 3]);
+    const elementIndicesBuffer = gl.createBuffer();
+    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, elementIndicesBuffer);
+    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, unitQuadElementIndices, gl.STATIC_DRAW);
+
+    // Setup a_cellpos, this is separate as it rarely changed
+    this._cellPositionBuffer = gl.createBuffer();
+    gl.bindBuffer(gl.ARRAY_BUFFER, this._cellPositionBuffer);
+    gl.enableVertexAttribArray(VertexAttribLocations.CELL_POSITION);
+    gl.vertexAttribPointer(VertexAttribLocations.CELL_POSITION, 2, gl.FLOAT, false, 0, 0);
+    gl.vertexAttribDivisor(VertexAttribLocations.CELL_POSITION, 1);
+
+    // Setup attributes
+    this._attributesBuffer = gl.createBuffer();
+    gl.bindBuffer(gl.ARRAY_BUFFER, this._attributesBuffer);
+    gl.enableVertexAttribArray(VertexAttribLocations.OFFSET);
+    gl.vertexAttribPointer(VertexAttribLocations.OFFSET, 2, gl.FLOAT, false, BYTES_PER_CELL, 0);
+    gl.vertexAttribDivisor(VertexAttribLocations.OFFSET, 1);
+    gl.enableVertexAttribArray(VertexAttribLocations.SIZE);
+    gl.vertexAttribPointer(VertexAttribLocations.SIZE, 2, gl.FLOAT, false, BYTES_PER_CELL, 2 * Float32Array.BYTES_PER_ELEMENT);
+    gl.vertexAttribDivisor(VertexAttribLocations.SIZE, 1);
+    gl.enableVertexAttribArray(VertexAttribLocations.TEXCOORD);
+    gl.vertexAttribPointer(VertexAttribLocations.TEXCOORD, 2, gl.FLOAT, false, BYTES_PER_CELL, 4 * Float32Array.BYTES_PER_ELEMENT);
+    gl.vertexAttribDivisor(VertexAttribLocations.TEXCOORD, 1);
+    gl.enableVertexAttribArray(VertexAttribLocations.TEXSIZE);
+    gl.vertexAttribPointer(VertexAttribLocations.TEXSIZE, 2, gl.FLOAT, false, BYTES_PER_CELL, 6 * Float32Array.BYTES_PER_ELEMENT);
+    gl.vertexAttribDivisor(VertexAttribLocations.TEXSIZE, 1);
+
+    // Setup empty texture atlas
+    this._atlasTexture = gl.createTexture();
+    gl.bindTexture(gl.TEXTURE_2D, this._atlasTexture);
+    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, 1, 1, 0, gl.RGBA, gl.UNSIGNED_BYTE, new Uint8Array([0, 0, 255, 255]));
+    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
+    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
+
+    // Allow drawing of transparent texture
+    gl.enable(gl.BLEND);
+    gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
+
+    // Set viewport
+    this.onResize();
+  }
+
+  public beginFrame(): boolean {
+    return this._atlas.beginFrame();
+  }
+
+  public updateCell(x: number, y: number, code: number, attr: number, bg: number, fg: number, chars: string): void {
+    this._updateCell(this._vertices.attributes, x, y, code, attr, bg, fg, chars);
+  }
+
+  private _updateCell(array: Float32Array, x: number, y: number, code: number, attr: number, bg: number, fg: number, chars?: string): void {
+    const terminal = this._terminal;
+
+    const i = ((y * terminal.cols) + x) * INDICES_PER_CELL;
+
+    // Exit early if this is a null/space character
+    if (code === NULL_CELL_CODE) {
+      array.fill(0, i, i + INDICES_PER_CELL - 1);
+      return;
+    }
+
+    let rasterizedGlyph: IRasterizedGlyph;
+    if (chars && chars.length > 1) {
+      rasterizedGlyph = this._atlas.getRasterizedGlyphCombinedChar(chars, attr, bg, fg, this._terminal.options.enableBold);
+    } else {
+      rasterizedGlyph = this._atlas.getRasterizedGlyph(code, attr, bg, fg, this._terminal.options.enableBold);
+    }
+
+    // Fill empty if no glyph was found
+    if (!rasterizedGlyph) {
+      array.fill(0, i, i + INDICES_PER_CELL - 1);
+      return;
+    }
+
+    // a_origin
+    array[i    ] = -rasterizedGlyph.offset.x + this._dimensions.scaledCharLeft;
+    array[i + 1] = -rasterizedGlyph.offset.y + this._dimensions.scaledCharTop;
+    // a_size
+    array[i + 2] = rasterizedGlyph.size.x / this._dimensions.scaledCanvasWidth;
+    array[i + 3] = rasterizedGlyph.size.y / this._dimensions.scaledCanvasHeight;
+    // a_texcoord
+    array[i + 4] = rasterizedGlyph.texturePositionClipSpace.x;
+    array[i + 5] = rasterizedGlyph.texturePositionClipSpace.y;
+    // a_texsize
+    array[i + 6] = rasterizedGlyph.sizeClipSpace.x;
+    array[i + 7] = rasterizedGlyph.sizeClipSpace.y;
+  }
+
+  public updateLineEnd(x: number, y: number): void {
+    // Clears all cells to the right of the line end
+    const i = (y * this._terminal.cols + x + 1) * INDICES_PER_CELL;
+    this._vertices.attributes.fill(0, i, i + (this._terminal.cols - this._lineLengths[y]) * INDICES_PER_CELL - 1);
+  }
+
+  public updateSelection(model: IRenderModel, columnSelectMode: boolean): void {
+    const terminal = this._terminal;
+
+    this._vertices.selectionAttributes = this._vertices.attributes.slice(0);
+
+    // TODO: Make fg and bg configurable, currently since the buffer doesn't
+    // support truecolor the char atlas cannot store it.
+    const fg = 0;
+    const bg = 7;
+
+    if (columnSelectMode) {
+      const startCol = model.selection.startCol;
+      const width = model.selection.endCol - startCol;
+      const height = model.selection.viewportCappedEndRow - model.selection.viewportCappedStartRow + 1;
+      for (let y = model.selection.viewportCappedStartRow; y < model.selection.viewportCappedStartRow + height; y++) {
+        this._updateSelectionRange(startCol, startCol + width, y, model, bg, fg);
+      }
+    } else {
+      // Draw first row
+      const startCol = model.selection.viewportStartRow === model.selection.viewportCappedStartRow ? model.selection.startCol : 0;
+      const startRowEndCol = model.selection.viewportCappedStartRow === model.selection.viewportCappedEndRow ? model.selection.endCol : terminal.cols;
+      this._updateSelectionRange(startCol, startRowEndCol, model.selection.viewportCappedStartRow, model, bg, fg);
+
+      // Draw middle rows
+      const middleRowsCount = Math.max(model.selection.viewportCappedEndRow - model.selection.viewportCappedStartRow - 1, 0);
+      for (let y = (model.selection.viewportCappedStartRow + 1); y <= model.selection.viewportCappedStartRow + middleRowsCount; y++) {
+        this._updateSelectionRange(0, startRowEndCol, y, model, bg, fg);
+      }
+
+      // Draw final row
+      if (model.selection.viewportCappedStartRow !== model.selection.viewportCappedEndRow) {
+        // Only draw viewportEndRow if it's not the same as viewportStartRow
+        const endCol = model.selection.viewportEndRow === model.selection.viewportCappedEndRow ? model.selection.endCol : terminal.cols;
+        this._updateSelectionRange(0, endCol, model.selection.viewportCappedEndRow, model, bg, fg);
+      }
+    }
+  }
+
+  private _updateSelectionRange(startCol: number, endCol: number, y: number, model: IRenderModel, bg: number, fg: number): void {
+    const terminal = this._terminal;
+    const row = y + terminal.buffer.ydisp;
+    let line: IBufferLine;
+    for (let x = startCol; x < endCol; x++) {
+      const offset = (y * this._terminal.cols + x) * INDICIES_PER_CELL;
+      // Because the cache uses attr as a lookup key it needs to contain the selection colors as well
+      let attr = model.cells[offset + 1];
+      attr = attr & ~0x3ffff | bg << 9 | fg;
+      const code = model.cells[offset];
+      if (code & COMBINED_CHAR_BIT_MASK) {
+        if (!line) {
+          line = terminal.buffer.lines.get(row);
+        }
+        const charData = line.get(x);
+        const chars = charData[CHAR_DATA_CHAR_INDEX];
+        this._updateCell(this._vertices.selectionAttributes, x, y, model.cells[offset], attr, bg, fg, chars);
+      } else {
+        this._updateCell(this._vertices.selectionAttributes, x, y, model.cells[offset], attr, bg, fg);
+      }
+    }
+  }
+
+  public onResize(): void {
+    const terminal = this._terminal;
+    const gl = this._gl;
+
+    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);
+
+    // Update vertices
+    const newCount = terminal.cols * terminal.rows * INDICES_PER_CELL;
+    if (this._vertices.count !== newCount) {
+      this._vertices.count = newCount;
+      this._vertices.attributes = new Float32Array(newCount);
+      this._lineLengths = new Int16Array(terminal.rows);
+
+      this._vertices.cellPosition = new Float32Array(terminal.cols * terminal.rows * 2);
+
+      let i = 0;
+      for (let y = 0; y < terminal.rows; y++) {
+        for (let x = 0; x < terminal.cols; x++) {
+          this._vertices.cellPosition[i++] = x / terminal.cols;
+          this._vertices.cellPosition[i++] = y / terminal.rows;
+        }
+      }
+    }
+  }
+
+  public onThemeChanged(): void {
+  }
+
+  public render(isSelectionVisible: boolean): void {
+    if (!this._atlas) {
+      return;
+    }
+
+    const gl = this._gl;
+
+    gl.useProgram(this._program);
+    gl.bindVertexArray(this._vertexArrayObject);
+
+    gl.bindBuffer(gl.ARRAY_BUFFER, this._cellPositionBuffer);
+    gl.bufferData(gl.ARRAY_BUFFER, this._vertices.cellPosition, gl.STATIC_DRAW);
+    gl.bindBuffer(gl.ARRAY_BUFFER, this._attributesBuffer);
+    gl.bufferData(gl.ARRAY_BUFFER, isSelectionVisible ? this._vertices.selectionAttributes : this._vertices.attributes, gl.DYNAMIC_DRAW);
+
+    // Bind the texture atlas if it's changed
+    if (this._atlas.hasCanvasChanged) {
+      this._atlas.hasCanvasChanged = false;
+      gl.uniform1i(this._textureLocation, 0);
+      gl.activeTexture(gl.TEXTURE0 + 0);
+      gl.bindTexture(gl.TEXTURE_2D, this._atlasTexture);
+      gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, this._atlas.cacheCanvas);
+      gl.generateMipmap(gl.TEXTURE_2D);
+    }
+
+    // Set uniforms
+    gl.uniformMatrix4fv(this._projectionLocation, false, PROJECTION_MATRIX);
+    gl.uniform2f(this._resolutionLocation, gl.canvas.width, gl.canvas.height);
+
+    // Draw the viewport
+    gl.drawElementsInstanced(gl.TRIANGLES, 6, gl.UNSIGNED_BYTE, 0, this._vertices.count / INDICES_PER_CELL);
+  }
+
+  public setAtlas(atlas: WebglCharAtlas): void {
+    const gl = this._gl;
+    this._atlas = atlas;
+
+    gl.bindTexture(gl.TEXTURE_2D, this._atlasTexture);
+    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, atlas.cacheCanvas);
+    gl.generateMipmap(gl.TEXTURE_2D);
+  }
+
+  public setDimensions(dimensions: IRenderDimensions): void {
+    this._dimensions = dimensions;
+  }
+}

src/renderer/webgl/RectangleRenderer.ts

@@ -0,0 +1,320 @@
+/**
+ * Copyright (c) 2018 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { ITerminal } from '../../Types';
+import { IColorManager, IRenderDimensions } from '../Types';
+import { createProgram, expandFloat32Array, PROJECTION_MATRIX } from './WebglUtils';
+import { IColor } from '../../shared/Types';
+import { IRenderModel, IWebGLVertexArrayObject, IWebGL2RenderingContext, ISelectionRenderModel } from './Types';
+import { RENDER_INVERTED_DEFAULT_COLOR } from './RenderModel';
+
+const enum VertexAttribLocations {
+  POSITION = 0,
+  SIZE = 1,
+  COLOR = 2,
+  UNIT_QUAD = 3
+}
+
+const vertexShaderSource = `#version 300 es
+layout (location = ${VertexAttribLocations.POSITION}) in vec2 a_position;
+layout (location = ${VertexAttribLocations.SIZE}) in vec2 a_size;
+layout (location = ${VertexAttribLocations.COLOR}) in vec3 a_color;
+layout (location = ${VertexAttribLocations.UNIT_QUAD}) in vec2 a_unitquad;
+
+uniform mat4 u_projection;
+uniform vec2 u_resolution;
+
+out vec3 v_color;
+
+void main() {
+  vec2 zeroToOne = (a_position + (a_unitquad * a_size)) / u_resolution;
+  gl_Position = u_projection * vec4(zeroToOne, 0.0, 1.0);
+  v_color = a_color;
+}`;
+
+const fragmentShaderSource = `#version 300 es
+precision mediump float;
+
+in vec3 v_color;
+
+out vec4 outColor;
+
+void main() {
+  outColor = vec4(v_color, 1);
+}`;
+
+interface IVertices {
+  attributes: Float32Array;
+  selection: Float32Array;
+  count: number;
+}
+
+const INDICES_PER_RECTANGLE = 8;
+const BYTES_PER_RECTANGLE = INDICES_PER_RECTANGLE * Float32Array.BYTES_PER_ELEMENT;
+
+const INITIAL_BUFFER_RECTANGLE_CAPACITY = 20 * INDICES_PER_RECTANGLE;
+
+export class RectangleRenderer {
+
+  private _program: WebGLProgram;
+  private _vertexArrayObject: IWebGLVertexArrayObject;
+  private _resolutionLocation: WebGLUniformLocation;
+  private _attributesBuffer: WebGLBuffer;
+  private _projectionLocation: WebGLUniformLocation;
+  private _bgFloat: Float32Array;
+  private _selectionFloat: Float32Array;
+
+  private _vertices: IVertices = {
+    count: 0,
+    attributes: new Float32Array(INITIAL_BUFFER_RECTANGLE_CAPACITY),
+    selection: new Float32Array(3 * INDICES_PER_RECTANGLE)
+  };
+
+  constructor(
+    private _terminal: ITerminal,
+    private _colorManager: IColorManager,
+    private _gl: IWebGL2RenderingContext,
+    private _dimensions: IRenderDimensions
+  ) {
+    const gl = this._gl;
+
+    this._program = createProgram(gl, vertexShaderSource, fragmentShaderSource);
+
+    // Uniform locations
+    this._resolutionLocation = gl.getUniformLocation(this._program, 'u_resolution');
+    this._projectionLocation = gl.getUniformLocation(this._program, 'u_projection');
+
+    // Create and set the vertex array object
+    this._vertexArrayObject = gl.createVertexArray();
+    gl.bindVertexArray(this._vertexArrayObject);
+
+    // Setup a_unitquad, this defines the 4 vertices of a rectangle
+    const unitQuadVertices = new Float32Array([0, 0, 1, 0, 0, 1, 1, 1]);
+    const unitQuadVerticesBuffer = gl.createBuffer();
+    gl.bindBuffer(gl.ARRAY_BUFFER, unitQuadVerticesBuffer);
+    gl.bufferData(gl.ARRAY_BUFFER, unitQuadVertices, gl.STATIC_DRAW);
+    gl.enableVertexAttribArray(VertexAttribLocations.UNIT_QUAD);
+    gl.vertexAttribPointer(VertexAttribLocations.UNIT_QUAD, 2, this._gl.FLOAT, false, 0, 0);
+
+    // Setup the unit quad element array buffer, this points to indices in
+    // unitQuadVertuces to allow is to draw 2 triangles from the vertices
+    const unitQuadElementIndices = new Uint8Array([0, 1, 3, 0, 2, 3]);
+    const elementIndicesBuffer = gl.createBuffer();
+    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, elementIndicesBuffer);
+    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, unitQuadElementIndices, gl.STATIC_DRAW);
+
+    // Setup attributes
+    this._attributesBuffer = gl.createBuffer();
+    gl.bindBuffer(gl.ARRAY_BUFFER, this._attributesBuffer);
+    gl.enableVertexAttribArray(VertexAttribLocations.POSITION);
+    gl.vertexAttribPointer(VertexAttribLocations.POSITION, 2, gl.FLOAT, false, BYTES_PER_RECTANGLE, 0);
+    gl.vertexAttribDivisor(VertexAttribLocations.POSITION, 1);
+    gl.enableVertexAttribArray(VertexAttribLocations.SIZE);
+    gl.vertexAttribPointer(VertexAttribLocations.SIZE, 2, gl.FLOAT, false, BYTES_PER_RECTANGLE, 2 * Float32Array.BYTES_PER_ELEMENT);
+    gl.vertexAttribDivisor(VertexAttribLocations.SIZE, 1);
+    gl.enableVertexAttribArray(VertexAttribLocations.COLOR);
+    gl.vertexAttribPointer(VertexAttribLocations.COLOR, 4, gl.FLOAT, false, BYTES_PER_RECTANGLE, 4 * Float32Array.BYTES_PER_ELEMENT);
+    gl.vertexAttribDivisor(VertexAttribLocations.COLOR, 1);
+
+    this._updateCachedColors();
+  }
+
+  public render(): void {
+    const gl = this._gl;
+
+    gl.useProgram(this._program);
+
+    gl.bindVertexArray(this._vertexArrayObject);
+
+    gl.uniformMatrix4fv(this._projectionLocation, false, PROJECTION_MATRIX);
+    gl.uniform2f(this._resolutionLocation, gl.canvas.width, gl.canvas.height);
+
+    // Bind attributes buffer and draw
+    gl.bindBuffer(gl.ARRAY_BUFFER, this._attributesBuffer);
+    gl.bufferData(gl.ARRAY_BUFFER, this._vertices.attributes, gl.DYNAMIC_DRAW);
+    gl.drawElementsInstanced(this._gl.TRIANGLES, 6, gl.UNSIGNED_BYTE, 0, this._vertices.count);
+
+    // Bind selection buffer and draw
+    gl.bindBuffer(gl.ARRAY_BUFFER, this._attributesBuffer);
+    gl.bufferData(gl.ARRAY_BUFFER, this._vertices.selection, gl.DYNAMIC_DRAW);
+    gl.drawElementsInstanced(this._gl.TRIANGLES, 6, gl.UNSIGNED_BYTE, 0, 3);
+  }
+
+  public onResize(): void {
+    this._updateViewportRectangle();
+  }
+
+  public onThemeChanged(): void {
+    this._updateCachedColors();
+    this._updateViewportRectangle();
+  }
+
+  private _updateCachedColors(): void {
+    this._bgFloat = this._colorToFloat32Array(this._colorManager.colors.background);
+    this._selectionFloat = this._colorToFloat32Array(this._colorManager.colors.selection);
+  }
+
+  private _updateViewportRectangle(): void {
+    // Set first rectangle that clears the screen
+    this._addRectangleFloat(
+      this._vertices.attributes,
+      0,
+      0,
+      0,
+      this._terminal.cols * this._dimensions.scaledCellWidth,
+      this._terminal.rows * this._dimensions.scaledCellHeight,
+      this._bgFloat
+    );
+  }
+
+  public updateSelection(model: ISelectionRenderModel, columnSelectMode: boolean): void {
+    const terminal = this._terminal;
+
+    if (!model.hasSelection) {
+      this._vertices.selection.fill(0, 0);
+      return;
+    }
+
+    if (columnSelectMode) {
+      const startCol = model.startCol;
+      const width = model.endCol - startCol;
+      const height = model.viewportCappedEndRow - model.viewportCappedStartRow + 1;
+      this._addRectangleFloat(
+        this._vertices.selection,
+        0,
+        startCol * this._dimensions.scaledCellWidth,
+        model.viewportCappedStartRow * this._dimensions.scaledCellHeight,
+        width * this._dimensions.scaledCellWidth,
+        height * this._dimensions.scaledCellHeight,
+        this._selectionFloat
+      );
+      this._vertices.selection.fill(0, INDICES_PER_RECTANGLE);
+    } else {
+      // Draw first row
+      const startCol = model.viewportStartRow === model.viewportCappedStartRow ? model.startCol : 0;
+      const startRowEndCol = model.viewportCappedStartRow === model.viewportCappedEndRow ? model.endCol : terminal.cols;
+      this._addRectangleFloat(
+        this._vertices.selection,
+        0,
+        startCol * this._dimensions.scaledCellWidth,
+        model.viewportCappedStartRow * this._dimensions.scaledCellHeight,
+        (startRowEndCol - startCol) * this._dimensions.scaledCellWidth,
+        this._dimensions.scaledCellHeight,
+        this._selectionFloat
+      );
+
+      // Draw middle rows
+      const middleRowsCount = Math.max(model.viewportCappedEndRow - model.viewportCappedStartRow - 1, 0);
+      this._addRectangleFloat(
+        this._vertices.selection,
+        INDICES_PER_RECTANGLE,
+        0,
+        (model.viewportCappedStartRow + 1) * this._dimensions.scaledCellHeight,
+        terminal.cols * this._dimensions.scaledCellWidth,
+        middleRowsCount * this._dimensions.scaledCellHeight,
+        this._selectionFloat
+      );
+
+      // Draw final row
+      if (model.viewportCappedStartRow !== model.viewportCappedEndRow) {
+        // Only draw viewportEndRow if it's not the same as viewportStartRow
+        const endCol = model.viewportEndRow === model.viewportCappedEndRow ? model.endCol : terminal.cols;
+        this._addRectangleFloat(
+          this._vertices.selection,
+          INDICES_PER_RECTANGLE * 2,
+          0,
+          model.viewportCappedEndRow * this._dimensions.scaledCellHeight,
+          endCol * this._dimensions.scaledCellWidth,
+          this._dimensions.scaledCellHeight,
+          this._selectionFloat
+        );
+      } else {
+        this._vertices.selection.fill(0, INDICES_PER_RECTANGLE * 2);
+      }
+    }
+  }
+
+  public updateBackgrounds(model: IRenderModel): void {
+    const terminal = this._terminal;
+    const vertices = this._vertices;
+
+    let rectangleCount = 1;
+
+    const DEFAULT_BACKGROUND_COLOR = 256;
+    for (let y = 0; y < terminal.rows; y++) {
+      let currentStartX = -1;
+      let currentBg = DEFAULT_BACKGROUND_COLOR;
+      for (let x = 0; x < terminal.cols; x++) {
+        const modelIndex = ((y * terminal.cols) + x) * 4;
+        const bg = model.cells[modelIndex + 2];
+        if (bg !== currentBg) {
+          // A rectangle needs to be drawn if going from non-default to another color
+          if (currentBg !== DEFAULT_BACKGROUND_COLOR) {
+            const offset = rectangleCount++ * INDICES_PER_RECTANGLE;
+            this._updateRectangle(vertices, offset, currentBg, currentStartX, x, y);
+          }
+          currentStartX = x;
+          currentBg = bg;
+        }
+      }
+      // Finish rectangle if it's still going
+      if (currentBg !== DEFAULT_BACKGROUND_COLOR) {
+        const offset = rectangleCount++ * INDICES_PER_RECTANGLE;
+        this._updateRectangle(vertices, offset, currentBg, currentStartX, terminal.cols, y);
+      }
+    }
+    vertices.count = rectangleCount;
+  }
+
+  private _updateRectangle(vertices: IVertices, offset: number, bg: number, startX: number, endX: number, y: number): void {
+    let color: IColor | null = null;
+    if (bg === RENDER_INVERTED_DEFAULT_COLOR) {
+      color = this._colorManager.colors.foreground;
+    } else if (bg < 256) {
+      color = this._colorManager.colors.ansi[bg];
+    }
+    if (vertices.attributes.length < offset + 4) {
+      vertices.attributes = expandFloat32Array(vertices.attributes, this._terminal.rows * this._terminal.cols * INDICES_PER_RECTANGLE);
+    }
+    const x1 = startX * this._dimensions.scaledCellWidth;
+    const y1 = y * this._dimensions.scaledCellHeight;
+    const r = ((color.rgba >> 24) & 0xFF) / 255;
+    const g = ((color.rgba >> 16) & 0xFF) / 255;
+    const b = ((color.rgba >> 8 ) & 0xFF) / 255;
+
+    this._addRectangle(vertices.attributes, offset, x1, y1, (endX - startX) * this._dimensions.scaledCellWidth, this._dimensions.scaledCellHeight, r, g, b, 1);
+  }
+
+  private _addRectangle(array: Float32Array, offset: number, x1: number, y1: number, width: number, height: number, r: number, g: number, b: number, a: number): void {
+    array[offset    ] = x1;
+    array[offset + 1] = y1;
+    array[offset + 2] = width;
+    array[offset + 3] = height;
+    array[offset + 4] = r;
+    array[offset + 5] = g;
+    array[offset + 6] = b;
+    array[offset + 7] = a;
+  }
+
+  private _addRectangleFloat(array: Float32Array, offset: number, x1: number, y1: number, width: number, height: number, color: Float32Array): void {
+    array[offset    ] = x1;
+    array[offset + 1] = y1;
+    array[offset + 2] = width;
+    array[offset + 3] = height;
+    array[offset + 4] = color[0];
+    array[offset + 5] = color[1];
+    array[offset + 6] = color[2];
+    array[offset + 7] = color[3];
+  }
+
+  private _colorToFloat32Array(color: IColor): Float32Array {
+    return new Float32Array([
+      ((color.rgba >> 24) & 0xFF) / 255,
+      ((color.rgba >> 16) & 0xFF) / 255,
+      ((color.rgba >> 8 ) & 0xFF) / 255,
+      ((color.rgba      ) & 0xFF) / 255
+    ]);
+  }
+}

src/renderer/webgl/RenderModel.ts

@@ -0,0 +1,59 @@
+/**
+ * Copyright (c) 2018 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { IRenderModel, ISelectionRenderModel } from './Types';
+
+export const RENDER_MODEL_INDICIES_PER_CELL = 4;
+
+// HACK: Cannot use INVERTED_DEFAULT_COLOR (-1) here because _model.cells is a
+// Uint32Array. This should be changed when true color is introduced to whatever
+// the mechanism is for the buffer.
+export const RENDER_INVERTED_DEFAULT_COLOR = 258;
+
+export const COMBINED_CHAR_BIT_MASK = 0x80000000;
+
+export class RenderModel implements IRenderModel {
+  public cells: Uint32Array;
+  public lineLengths: Uint32Array;
+  public selection: ISelectionRenderModel;
+
+  constructor() {
+    this.cells = new Uint32Array(0);
+    this.lineLengths = new Uint32Array(0);
+    this.selection = {
+      hasSelection: false,
+      viewportStartRow: 0,
+      viewportEndRow: 0,
+      viewportCappedStartRow: 0,
+      viewportCappedEndRow: 0,
+      startCol: 0,
+      endCol: 0
+    };
+  }
+
+  public resize(cols: number, rows: number): void {
+    const indexCount = cols * rows * RENDER_MODEL_INDICIES_PER_CELL;
+    if (indexCount !== this.cells.length) {
+      this.cells = new Uint32Array(indexCount);
+      this.lineLengths = new Uint32Array(rows);
+    }
+  }
+
+  public clear(): void {
+    this.cells.fill(0, 0);
+    this.lineLengths.fill(0, 0);
+    this.clearSelection();
+  }
+
+  public clearSelection(): void {
+    this.selection.hasSelection = false;
+    this.selection.viewportStartRow = 0;
+    this.selection.viewportEndRow = 0;
+    this.selection.viewportCappedStartRow = 0;
+    this.selection.viewportCappedEndRow = 0;
+    this.selection.startCol = 0;
+    this.selection.endCol = 0;
+  }
+}

src/renderer/webgl/Types.ts

@@ -0,0 +1,75 @@
+/**
+ * Copyright (c) 2018 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+export interface IRasterizedGlyphSet {
+  [flags: number]: IRasterizedGlyph;
+}
+
+/**
+ * Represents a rasterized glyph within a texture atlas. Some numbers are
+ * tracked in CSS pixels as well in order to reduce calculations during the
+ * render loop.
+ */
+export interface IRasterizedGlyph {
+  /**
+   * The x and y offset between the glyph's top/left and the top/left of a cell
+   * in pixels.
+   */
+  offset: IVector;
+  /**
+   * the x and y position of the glyph in the texture in pixels.
+   */
+  texturePosition: IVector;
+  /**
+   * the x and y position of the glyph in the texture in clip space coordinates.
+   */
+  texturePositionClipSpace: IVector;
+  /**
+   * The width and height of the glyph in the texture in pixels.
+   */
+  size: IVector;
+  /**
+   * The width and height of the glyph in the texture in clip space coordinates.
+   */
+  sizeClipSpace: IVector;
+}
+
+export interface IVector {
+  x: number;
+  y: number;
+}
+
+export interface IBoundingBox {
+  top: number;
+  left: number;
+  right: number;
+  bottom: number;
+}
+
+export interface IRenderModel {
+  cells: Uint32Array;
+  lineLengths: Uint32Array;
+  selection: ISelectionRenderModel;
+}
+
+export interface ISelectionRenderModel {
+  hasSelection: boolean;
+  viewportStartRow: number;
+  viewportEndRow: number;
+  viewportCappedStartRow: number;
+  viewportCappedEndRow: number;
+  startCol: number;
+  endCol: number;
+}
+
+export interface IWebGL2RenderingContext extends WebGLRenderingContext {
+  vertexAttribDivisor(index: number, divisor: number): void;
+  createVertexArray(): IWebGLVertexArrayObject;
+  bindVertexArray(vao: IWebGLVertexArrayObject): void;
+  drawElementsInstanced(mode: number, count: number, type: number, offset: number, instanceCount: number): void;
+}
+
+export interface IWebGLVertexArrayObject {
+}

src/renderer/webgl/WebglCharAtlas.ts

@@ -0,0 +1,386 @@
+/**
+ * Copyright (c) 2017 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { DIM_OPACITY, IGlyphIdentifier } from '../atlas/Types';
+import { ICharAtlasConfig } from '../../shared/atlas/Types';
+import { IColor } from '../../shared/Types';
+import BaseCharAtlas from '../atlas/BaseCharAtlas';
+import { DEFAULT_ANSI_COLORS } from '../ColorManager';
+import { clearColor } from '../../shared/atlas/CharAtlasGenerator';
+import { IRasterizedGlyph, IBoundingBox, IRasterizedGlyphSet } from './Types';
+import { DEFAULT_ATTR } from '../../Buffer';
+import { FLAGS } from '../Types';
+import { RENDER_INVERTED_DEFAULT_COLOR } from './RenderModel';
+
+// In practice we're probably never going to exhaust a texture this large. For debugging purposes,
+// however, it can be useful to set this to a really tiny value, to verify that LRU eviction works.
+const TEXTURE_WIDTH = 1024;
+const TEXTURE_HEIGHT = 1024;
+
+/**
+ * The amount of the texture to be filled before throwing it away and starting
+ * again. Since the throw away and individual glyph draws don't cost too much,
+ * this prevent juggling multiple textures in the GL context.
+ */
+const TEXTURE_CAPACITY = Math.floor(TEXTURE_HEIGHT * 0.8);
+
+const TRANSPARENT_COLOR = {
+  css: 'rgba(0, 0, 0, 0)',
+  rgba: 0
+};
+
+/**
+ * A shared object which is used to draw nothing for a particular cell.
+ */
+const NULL_RASTERIZED_GLYPH: IRasterizedGlyph = {
+  offset: { x: 0, y: 0 },
+  texturePosition: { x: 0, y: 0 },
+  texturePositionClipSpace: { x: 0, y: 0 },
+  size: { x: 0, y: 0 },
+  sizeClipSpace: { x: 0, y: 0 }
+};
+
+const TMP_CANVAS_GLYPH_PADDING = 2;
+
+export default class WebglCharAtlas extends BaseCharAtlas {
+  private _cacheMap: { [code: number]: IRasterizedGlyphSet } = {};
+  private _cacheMapCombined: { [chars: string]: IRasterizedGlyphSet } = {};
+
+  // The texture that the atlas is drawn to
+  public cacheCanvas: HTMLCanvasElement;
+  private _cacheCtx: CanvasRenderingContext2D;
+
+  private _tmpCanvas: HTMLCanvasElement;
+  // A temporary context that glyphs are drawn to before being transfered to the atlas.
+  private _tmpCtx: CanvasRenderingContext2D;
+
+  // Since glyphs are expected to be around the same height, the packing
+  // strategy used it to fill a row with glyphs while keeping track of the
+  // tallest glyph in the row. Once the row is full a new row is started at
+  // (0,lastRow+lastRowTallestGlyph).
+  private _currentRowY: number = 0;
+  private _currentRowX: number = 0;
+  private _currentRowHeight: number = 0;
+
+  public hasCanvasChanged = false;
+
+  private _workBoundingBox: IBoundingBox = { top: 0, left: 0, bottom: 0, right: 0 };
+
+  constructor(document: Document, private _config: ICharAtlasConfig) {
+    super();
+
+    this.cacheCanvas = document.createElement('canvas');
+    this.cacheCanvas.width = TEXTURE_WIDTH;
+    this.cacheCanvas.height = TEXTURE_HEIGHT;
+    // The canvas needs alpha because we use clearColor to convert the background color to alpha.
+    // It might also contain some characters with transparent backgrounds if allowTransparency is
+    // set.
+    this._cacheCtx = this.cacheCanvas.getContext('2d', {alpha: true});
+
+    this._tmpCanvas = document.createElement('canvas');
+    this._tmpCanvas.width = this._config.scaledCharWidth * 2 + TMP_CANVAS_GLYPH_PADDING * 2;
+    this._tmpCanvas.height = this._config.scaledCharHeight + TMP_CANVAS_GLYPH_PADDING * 2;
+    this._tmpCtx = this._tmpCanvas.getContext('2d', {alpha: this._config.allowTransparency});
+
+    // This is useful for debugging
+    document.body.appendChild(this.cacheCanvas);
+  }
+
+  public dispose(): void {
+    if (this.cacheCanvas.parentElement) {
+      this.cacheCanvas.parentElement.removeChild(this.cacheCanvas);
+    }
+  }
+
+  protected _doWarmUp(): void {
+    // Pre-fill with ASCII 33-126
+    for (let i = 33; i < 126; i++) {
+      const rasterizedGlyph = this._drawToCache(i, DEFAULT_ATTR, 256, 257, true);
+      this._cacheMap[i] = {
+        [DEFAULT_ATTR]: rasterizedGlyph
+      };
+    }
+  }
+
+  public beginFrame(): boolean {
+    if (this._currentRowY > TEXTURE_CAPACITY) {
+      this._cacheCtx.clearRect(0, 0, TEXTURE_WIDTH, TEXTURE_HEIGHT);
+      this._cacheMap = {};
+      this._currentRowHeight = 0;
+      this._currentRowX = 0;
+      this._currentRowY = 0;
+      this._doWarmUp();
+      return true;
+    }
+    return false;
+  }
+
+  public getRasterizedGlyphCombinedChar(chars: string, attr: number, bg: number, fg: number, enableBold: boolean): IRasterizedGlyph {
+    let rasterizedGlyphSet = this._cacheMapCombined[chars];
+    if (!rasterizedGlyphSet) {
+      rasterizedGlyphSet = {};
+      this._cacheMapCombined[chars] = rasterizedGlyphSet;
+    }
+    let rasterizedGlyph = rasterizedGlyphSet[attr];
+    if (!rasterizedGlyph) {
+      rasterizedGlyph = this._drawToCache(chars, attr, bg, fg, enableBold);
+      rasterizedGlyphSet[attr] = rasterizedGlyph;
+    }
+    return rasterizedGlyph;
+  }
+
+  /**
+   * Gets the glyphs texture coords, drawing the texture if it's not already
+   */
+  public getRasterizedGlyph(code: number, attr: number, bg: number, fg: number, enableBold: boolean): IRasterizedGlyph {
+    // Space is always an empty cell, special case this as it's so common
+    if (code === 32) {
+      return;
+    }
+
+    let rasterizedGlyphSet = this._cacheMap[code];
+    if (!rasterizedGlyphSet) {
+      rasterizedGlyphSet = {};
+      this._cacheMap[code] = rasterizedGlyphSet;
+    }
+    let rasterizedGlyph = rasterizedGlyphSet[attr];
+    if (!rasterizedGlyph) {
+      rasterizedGlyph = this._drawToCache(code, attr, bg, fg, enableBold);
+      rasterizedGlyphSet[attr] = rasterizedGlyph;
+    }
+    return rasterizedGlyph;
+  }
+
+  public draw(
+    ctx: CanvasRenderingContext2D,
+    glyph: IGlyphIdentifier,
+    x: number,
+    y: number
+  ): boolean {
+    throw new Error('WebglCharAtlas is only compatible with the webgl renderer');
+  }
+
+  private _getColorFromAnsiIndex(idx: number): IColor {
+    if (idx < this._config.colors.ansi.length) {
+      return this._config.colors.ansi[idx];
+    }
+    return DEFAULT_ANSI_COLORS[idx];
+  }
+
+  private _getBackgroundColor(bg: number): IColor {
+    if (this._config.allowTransparency) {
+      // The background color might have some transparency, so we need to render it as fully
+      // transparent in the atlas. Otherwise we'd end up drawing the transparent background twice
+      // around the anti-aliased edges of the glyph, and it would look too dark.
+      return TRANSPARENT_COLOR;
+    } else if (bg === RENDER_INVERTED_DEFAULT_COLOR) {
+      return this._config.colors.foreground;
+    } else if (bg < 256) {
+      return this._getColorFromAnsiIndex(bg);
+    }
+    return this._config.colors.background;
+  }
+
+  private _getForegroundColor(fg: number): IColor {
+    if (fg === RENDER_INVERTED_DEFAULT_COLOR) {
+      return this._config.colors.background;
+    } else if (fg < 256) {
+      // 256 color support
+      return this._getColorFromAnsiIndex(fg);
+    }
+    return this._config.colors.foreground;
+  }
+
+  private _drawToCache(code: number, attr: number, bg: number, fg: number, enableBold: boolean): IRasterizedGlyph;
+  private _drawToCache(chars: string, attr: number, bg: number, fg: number, enableBold: boolean): IRasterizedGlyph;
+  private _drawToCache(codeOrChars: number | string, attr: number, bg: number, fg: number, enableBold: boolean): IRasterizedGlyph {
+    const chars = typeof codeOrChars === 'number' ? String.fromCharCode(codeOrChars) : codeOrChars;
+
+    this.hasCanvasChanged = true;
+
+    const flags = attr >> 18;
+
+    const bold = !!(flags & FLAGS.BOLD) && enableBold;
+    const dim = !!(flags & FLAGS.DIM);
+    const italic = !!(flags & FLAGS.ITALIC);
+
+    this._tmpCtx.save();
+
+    // draw the background
+    const backgroundColor = this._getBackgroundColor(bg);
+    // Use a 'copy' composite operation to clear any existing glyph out of _tmpCtxWithAlpha, regardless of
+    // transparency in backgroundColor
+    this._tmpCtx.globalCompositeOperation = 'copy';
+    this._tmpCtx.fillStyle = backgroundColor.css;
+    this._tmpCtx.fillRect(0, 0, this._tmpCanvas.width, this._tmpCanvas.height);
+    this._tmpCtx.globalCompositeOperation = 'source-over';
+
+    // draw the foreground/glyph
+    const fontWeight = bold ? this._config.fontWeightBold : this._config.fontWeight;
+    const fontStyle = italic ? 'italic' : '';
+    this._tmpCtx.font =
+      `${fontStyle} ${fontWeight} ${this._config.fontSize * this._config.devicePixelRatio}px ${this._config.fontFamily}`;
+    this._tmpCtx.textBaseline = 'top';
+
+    this._tmpCtx.fillStyle = this._getForegroundColor(fg).css;
+
+    // Apply alpha to dim the character
+    if (dim) {
+      this._tmpCtx.globalAlpha = DIM_OPACITY;
+    }
+
+    // Draw the character
+    this._tmpCtx.fillText(chars, TMP_CANVAS_GLYPH_PADDING, TMP_CANVAS_GLYPH_PADDING);
+    this._tmpCtx.restore();
+
+    // clear the background from the character to avoid issues with drawing over the previous
+    // character if it extends past it's bounds
+    const imageData = this._tmpCtx.getImageData(
+      0, 0, this._tmpCanvas.width, this._tmpCanvas.height
+    );
+
+    // TODO: Support transparency
+    // let isEmpty = false;
+    // if (!this._config.allowTransparency) {
+    //   isEmpty = clearColor(imageData, backgroundColor);
+    // }
+
+    // Clear out the background color and determine if the glyph is empty.
+    const isEmpty = clearColor(imageData, backgroundColor);
+
+    // Handle empty glyphs
+    if (isEmpty) {
+      return NULL_RASTERIZED_GLYPH;
+    }
+
+    const rasterizedGlyph = this._findGlyphBoundingBox(imageData, this._workBoundingBox);
+    const clippedImageData = this._clipImageData(imageData, this._workBoundingBox);
+
+    // Check if there is enough room in the current row and go to next if needed
+    if (this._currentRowX + this._config.scaledCharWidth > TEXTURE_WIDTH) {
+      this._currentRowX = 0;
+      this._currentRowY += this._currentRowHeight;
+      this._currentRowHeight = 0;
+    }
+
+    // Record texture position
+    rasterizedGlyph.texturePosition.x = this._currentRowX;
+    rasterizedGlyph.texturePosition.y = this._currentRowY;
+    rasterizedGlyph.texturePositionClipSpace.x = this._currentRowX / TEXTURE_WIDTH;
+    rasterizedGlyph.texturePositionClipSpace.y = this._currentRowY / TEXTURE_HEIGHT;
+
+    // Update atlas current row
+    this._currentRowHeight = Math.max(this._currentRowHeight, rasterizedGlyph.size.y);
+    this._currentRowX += rasterizedGlyph.size.x;
+
+    // putImageData doesn't do any blending, so it will overwrite any existing cache entry for us
+    this._cacheCtx.putImageData(clippedImageData, rasterizedGlyph.texturePosition.x, rasterizedGlyph.texturePosition.y);
+
+    return rasterizedGlyph;
+  }
+
+  /**
+   * Given an ImageData object, find the bounding box of the non-transparent
+   * portion of the texture and return an IRasterizedGlyph with these
+   * dimensions.
+   * @param imageData The image data to read.
+   * @param boundingBox An IBoundingBox to put the clipped bounding box values.
+   */
+  private _findGlyphBoundingBox(imageData: ImageData, boundingBox: IBoundingBox): IRasterizedGlyph {
+    boundingBox.top = 0;
+    let found = false;
+    for (let y = 0; y < this._tmpCanvas.height; y++) {
+      for (let x = 0; x < this._tmpCanvas.width; x++) {
+        const alphaOffset = y * this._tmpCanvas.width * 4 + x * 4 + 3;
+        if (imageData.data[alphaOffset] !== 0) {
+          boundingBox.top = y;
+          found = true;
+          break;
+        }
+      }
+      if (found) {
+        break;
+      }
+    }
+    boundingBox.left = 0;
+    found = false;
+    for (let x = 0; x < this._tmpCanvas.width; x++) {
+      for (let y = 0; y < this._tmpCanvas.height; y++) {
+        const alphaOffset = y * this._tmpCanvas.width * 4 + x * 4 + 3;
+        if (imageData.data[alphaOffset] !== 0) {
+          boundingBox.left = x;
+          found = true;
+          break;
+        }
+      }
+      if (found) {
+        break;
+      }
+    }
+    boundingBox.right = this._tmpCanvas.width;
+    found = false;
+    for (let x = this._tmpCanvas.width - 1; x >= 0; x--) {
+      for (let y = 0; y < this._tmpCanvas.height; y++) {
+        const alphaOffset = y * this._tmpCanvas.width * 4 + x * 4 + 3;
+        if (imageData.data[alphaOffset] !== 0) {
+          boundingBox.right = x;
+          found = true;
+          break;
+        }
+      }
+      if (found) {
+        break;
+      }
+    }
+    boundingBox.bottom = this._tmpCanvas.height;
+    found = false;
+    for (let y = this._tmpCanvas.height - 1; y >= 0; y--) {
+      for (let x = 0; x < this._tmpCanvas.width; x++) {
+        const alphaOffset = y * this._tmpCanvas.width * 4 + x * 4 + 3;
+        if (imageData.data[alphaOffset] !== 0) {
+          boundingBox.bottom = y;
+          found = true;
+          break;
+        }
+      }
+      if (found) {
+        break;
+      }
+    }
+    return {
+      texturePosition: { x: 0, y: 0 },
+      texturePositionClipSpace: { x: 0, y: 0 },
+      size: {
+        x: boundingBox.right - boundingBox.left + 1,
+        y: boundingBox.bottom - boundingBox.top + 1
+      },
+      sizeClipSpace: {
+        x: (boundingBox.right - boundingBox.left + 1) / TEXTURE_WIDTH,
+        y: (boundingBox.bottom - boundingBox.top + 1) / TEXTURE_HEIGHT
+      },
+      offset: {
+        x: -boundingBox.left + TMP_CANVAS_GLYPH_PADDING,
+        y: -boundingBox.top + TMP_CANVAS_GLYPH_PADDING
+      }
+    };
+  }
+
+  private _clipImageData(imageData: ImageData, boundingBox: IBoundingBox): ImageData {
+    const width = boundingBox.right - boundingBox.left + 1;
+    const height = boundingBox.bottom - boundingBox.top + 1;
+    const clippedData = new Uint8ClampedArray(width * height * 4);
+    for (let y = boundingBox.top; y <= boundingBox.bottom; y++) {
+      for (let x = boundingBox.left; x <= boundingBox.right; x++) {
+        const oldOffset = y * this._tmpCanvas.width * 4 + x * 4;
+        const newOffset = (y - boundingBox.top) * width * 4 + (x - boundingBox.left) * 4;
+        clippedData[newOffset] = imageData.data[oldOffset];
+        clippedData[newOffset + 1] = imageData.data[oldOffset + 1];
+        clippedData[newOffset + 2] = imageData.data[oldOffset + 2];
+        clippedData[newOffset + 3] = imageData.data[oldOffset + 3];
+      }
+    }
+    return new ImageData(clippedData, width, height);
+  }
+}

src/renderer/webgl/WebglRenderer.ts

@@ -0,0 +1,427 @@
+/**
+ * Copyright (c) 2018 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { EventEmitter } from '../../common/EventEmitter';
+import { IRenderer, IRenderDimensions, IColorSet, IRenderLayer, FLAGS } from '../Types';
+import { ITheme } from 'xterm';
+import { CharacterJoinerHandler, ITerminal } from '../../Types';
+import { ColorManager } from '../ColorManager';
+import { RenderDebouncer } from '../../ui/RenderDebouncer';
+import { GlyphRenderer } from './GlyphRenderer';
+import { LinkRenderLayer } from '../LinkRenderLayer';
+import { CursorRenderLayer } from '../CursorRenderLayer';
+import { acquireCharAtlas } from '../atlas/CharAtlasCache';
+import WebglCharAtlas from './WebglCharAtlas';
+import { ScreenDprMonitor } from '../../ui/ScreenDprMonitor';
+import { RectangleRenderer } from './RectangleRenderer';
+import { CHAR_DATA_ATTR_INDEX, CHAR_DATA_CODE_INDEX, CHAR_DATA_CHAR_INDEX } from '../../Buffer';
+import { IWebGL2RenderingContext } from './Types';
+import { INVERTED_DEFAULT_COLOR } from '../atlas/Types';
+import { RenderModel, RENDER_INVERTED_DEFAULT_COLOR, COMBINED_CHAR_BIT_MASK } from './RenderModel';
+
+export const INDICIES_PER_CELL = 4;
+
+export class WebglRenderer extends EventEmitter implements IRenderer {
+  private _renderDebouncer: RenderDebouncer;
+  private _renderLayers: IRenderLayer[];
+  private _charAtlas: WebglCharAtlas;
+  private _screenDprMonitor: ScreenDprMonitor;
+  private _devicePixelRatio: number;
+
+  private _model: RenderModel = new RenderModel();
+
+  private _canvas: HTMLCanvasElement;
+  private _gl: IWebGL2RenderingContext;
+  private _rectangleRenderer: RectangleRenderer;
+  private _glyphRenderer: GlyphRenderer;
+
+  private _isPaused: boolean = false;
+  private _needsFullRefresh: boolean = false;
+
+  public dimensions: IRenderDimensions;
+  public colorManager: ColorManager;
+
+  constructor(
+    private _terminal: ITerminal,
+    theme: ITheme
+  ) {
+    super();
+    const allowTransparency = this._terminal.options.allowTransparency;
+    this.colorManager = new ColorManager(document, allowTransparency);
+
+    this._renderLayers = [
+      new LinkRenderLayer(this._terminal.screenElement, 2, this.colorManager.colors, this._terminal),
+      new CursorRenderLayer(this._terminal.screenElement, 3, this.colorManager.colors)
+    ];
+    this.dimensions = {
+      scaledCharWidth: null,
+      scaledCharHeight: null,
+      scaledCellWidth: null,
+      scaledCellHeight: null,
+      scaledCharLeft: null,
+      scaledCharTop: null,
+      scaledCanvasWidth: null,
+      scaledCanvasHeight: null,
+      canvasWidth: null,
+      canvasHeight: null,
+      actualCellWidth: null,
+      actualCellHeight: null
+    };
+    this._devicePixelRatio = window.devicePixelRatio;
+    this._updateDimensions();
+
+    this._screenDprMonitor = new ScreenDprMonitor();
+    this._screenDprMonitor.setListener(() => this.onWindowResize(window.devicePixelRatio));
+    this.register(this._screenDprMonitor);
+
+    this._renderDebouncer = new RenderDebouncer(this._terminal, this._renderRows.bind(this));
+
+    this._canvas = document.createElement('canvas');
+    this._gl = this._canvas.getContext('webgl2') as IWebGL2RenderingContext;
+    if (!this._gl) {
+        throw new Error('WebGL2 not supported');
+    }
+    this._terminal.screenElement.appendChild(this._canvas);
+
+    this._rectangleRenderer = new RectangleRenderer(this._terminal, this.colorManager, this._gl, this.dimensions);
+    this._glyphRenderer = new GlyphRenderer(this._terminal, this._gl, this.dimensions);
+
+    // Detect whether IntersectionObserver is detected and enable renderer pause
+    // and resume based on terminal visibility if so
+    if ('IntersectionObserver' in window) {
+      const observer = new IntersectionObserver(e => this.onIntersectionChange(e[0]), { threshold: 0 });
+      observer.observe(this._terminal.element);
+      this.register({ dispose: () => observer.disconnect() });
+    }
+  }
+
+  public dispose(): void {
+    this._renderLayers.forEach(l => l.dispose());
+    this._terminal.screenElement.removeChild(this._canvas);
+  }
+
+  public onIntersectionChange(entry: IntersectionObserverEntry): void {
+    this._isPaused = entry.intersectionRatio === 0;
+    if (!this._isPaused && this._needsFullRefresh) {
+      this._terminal.refresh(0, this._terminal.rows - 1);
+    }
+  }
+
+  private _refreshViewport(): void {
+    // Force a refresh
+    this._model.clear();
+    if (this._isPaused) {
+      this._needsFullRefresh = true;
+    } else {
+      this._terminal.refresh(0, this._terminal.rows - 1);
+    }
+  }
+
+  public setTheme(theme: ITheme | undefined): IColorSet {
+    if (theme) {
+      this.colorManager.setTheme(theme);
+    }
+
+    // Clear layers and force a full render
+    this._renderLayers.forEach(l => {
+      l.onThemeChanged(this._terminal, this.colorManager.colors);
+      l.reset(this._terminal);
+    });
+
+    this._rectangleRenderer.onThemeChanged();
+    this._glyphRenderer.onThemeChanged();
+
+    this._refreshCharAtlas();
+    this._refreshViewport();
+
+    return this.colorManager.colors;
+  }
+
+  public onWindowResize(devicePixelRatio: number): void {
+    // If the device pixel ratio changed, the char atlas needs to be regenerated
+    // and the terminal needs to refreshed
+    if (this._devicePixelRatio !== devicePixelRatio) {
+      this._devicePixelRatio = devicePixelRatio;
+      this.onResize(this._terminal.cols, this._terminal.rows, devicePixelRatio);
+    }
+  }
+
+  public onResize(cols: number, rows: number, devicePixelRatio: number = window.devicePixelRatio): void {
+    // Update character and canvas dimensions
+    this._updateDimensions(devicePixelRatio);
+
+    this._model.resize(this._terminal.cols, this._terminal.rows);
+    this._rectangleRenderer.onResize();
+
+    // Resize all render layers
+    this._renderLayers.forEach(l => l.resize(this._terminal, this.dimensions));
+
+    // Resize the canvas
+    this._canvas.width = this.dimensions.scaledCanvasWidth;
+    this._canvas.height = this.dimensions.scaledCanvasHeight;
+    this._canvas.style.width = `${this.dimensions.canvasWidth}px`;
+    this._canvas.style.height = `${this.dimensions.canvasHeight}px`;
+
+    // Resize the screen
+    this._terminal.screenElement.style.width = `${this.dimensions.canvasWidth}px`;
+    this._terminal.screenElement.style.height = `${this.dimensions.canvasHeight}px`;
+    this._glyphRenderer.setDimensions(this.dimensions);
+    this._glyphRenderer.onResize();
+
+    this._refreshCharAtlas(devicePixelRatio);
+    this._refreshViewport();
+
+    this.emit('resize', {
+      width: this.dimensions.canvasWidth,
+      height: this.dimensions.canvasHeight
+    });
+  }
+
+  public onCharSizeChanged(): void {
+    this.onResize(this._terminal.cols, this._terminal.rows);
+  }
+
+  public onBlur(): void {
+    this._renderLayers.forEach(l => l.onBlur(this._terminal));
+  }
+
+  public onFocus(): void {
+    this._renderLayers.forEach(l => l.onFocus(this._terminal));
+  }
+
+  public onSelectionChanged(start: [number, number], end: [number, number], columnSelectMode: boolean): void {
+    this._renderLayers.forEach(l => l.onSelectionChanged(this._terminal, start, end, columnSelectMode));
+
+    this._updateSelectionModel(start, end);
+
+    this._rectangleRenderer.updateSelection(this._model.selection, columnSelectMode);
+    this._glyphRenderer.updateSelection(this._model, columnSelectMode);
+    this.refreshRows(0, this._terminal.rows - 1);
+  }
+
+  public onCursorMove(): void {
+    this._renderLayers.forEach(l => l.onCursorMove(this._terminal));
+  }
+
+  public onOptionsChanged(): void {
+    this._renderLayers.forEach(l => l.onOptionsChanged(this._terminal));
+    this._updateDimensions();
+    this._refreshCharAtlas();
+  }
+
+  /**
+   * Refreshes the char atlas, aquiring a new one if necessary.
+   * @param terminal The terminal.
+   * @param colorSet The color set to use for the char atlas.
+   */
+  private _refreshCharAtlas(devicePixelRatio: number = window.devicePixelRatio): void {
+    if (this.dimensions.scaledCharWidth <= 0 && this.dimensions.scaledCharHeight <= 0) {
+      return;
+    }
+
+    const atlas = acquireCharAtlas(this._terminal, this.colorManager.colors, this.dimensions.scaledCharWidth, this.dimensions.scaledCharHeight, devicePixelRatio);
+    if (!('getRasterizedGlyph' in atlas)) {
+      throw new Error('The webgl renderer only works with the webgl char atlas');
+    }
+    this._charAtlas = atlas as WebglCharAtlas;
+    this._charAtlas.warmUp();
+    this._glyphRenderer.setAtlas(this._charAtlas);
+  }
+
+  public clear(): void {
+    this._renderLayers.forEach(l => l.reset(this._terminal));
+  }
+
+  public refreshRows(start: number, end: number): void {
+    if (this._isPaused) {
+      this._needsFullRefresh = true;
+      return;
+    }
+    this._renderDebouncer.refresh(start, end);
+  }
+
+  public registerCharacterJoiner(handler: CharacterJoinerHandler): number {
+    return -1;
+  }
+
+  public deregisterCharacterJoiner(joinerId: number): boolean {
+    return false;
+  }
+
+  private _renderRows(start: number, end: number): void {
+    // Update render layers
+    this._renderLayers.forEach(l => l.onGridChanged(this._terminal, start, end));
+
+    // Tell renderer the frame is beginning
+    if (this._glyphRenderer.beginFrame()) {
+      this._model.clear();
+    }
+
+    // Update model to reflect what's drawn
+    this._updateModel(start, end);
+
+    // Render
+    this._rectangleRenderer.render();
+    this._glyphRenderer.render(this._model.selection.hasSelection);
+
+    // Emit event
+    this._terminal.emit('refresh', { start, end });
+  }
+
+  private _updateModel(start: number, end: number): void {
+    const terminal = this._terminal;
+
+    for (let y = start; y <= end; y++) {
+      const row = y + terminal.buffer.ydisp;
+      const line = terminal.buffer.lines.get(row);
+      this._model.lineLengths[y] = 0;
+      for (let x = 0; x < terminal.cols; x++) {
+        const charData = line.get(x);
+        const chars = charData[CHAR_DATA_CHAR_INDEX];
+        let code = charData[CHAR_DATA_CODE_INDEX];
+        const attr = charData[CHAR_DATA_ATTR_INDEX];
+        const i = ((y * terminal.cols) + x) * INDICIES_PER_CELL;
+
+        // Nothing has changed, no updates needed
+        if (this._model.cells[i] === code && this._model.cells[i + 1] === attr) {
+          continue;
+        }
+
+        // Resolve bg and fg and cache in the model
+        const flags = attr >> 18;
+        let bg = attr & 0x1ff;
+        let fg = (attr >> 9) & 0x1ff;
+
+        // If inverse flag is on, the foreground should become the background.
+        if (flags & FLAGS.INVERSE) {
+          const temp = bg;
+          bg = fg;
+          fg = temp;
+          if (fg === 256) {
+            fg = RENDER_INVERTED_DEFAULT_COLOR;
+          }
+          if (bg === 257) {
+            bg = RENDER_INVERTED_DEFAULT_COLOR;
+          }
+        }
+        const drawInBrightColor = terminal.options.drawBoldTextInBrightColors && !!(flags & FLAGS.BOLD) && fg < 8 && fg !== INVERTED_DEFAULT_COLOR;
+        fg += drawInBrightColor ? 8 : 0;
+
+        // Flag combined chars with a bit mask so they're easily identifiable
+        if (chars.length > 1) {
+          code = code | COMBINED_CHAR_BIT_MASK;
+        }
+
+        this._model.cells[i    ] = code;
+        this._model.cells[i + 1] = attr;
+        this._model.cells[i + 2] = bg;
+        this._model.cells[i + 3] = fg;
+
+        this._glyphRenderer.updateCell(x, y, code, attr, bg, fg, chars);
+      }
+    }
+    this._rectangleRenderer.updateBackgrounds(this._model);
+  }
+
+  private _updateSelectionModel(start: [number, number], end: [number, number]): void {
+    const terminal = this._terminal;
+
+    // Selection does not exist
+    if (!start || !end || (start[0] === end[0] && start[1] === end[1])) {
+      this._model.clearSelection();
+      return;
+    }
+
+    // Translate from buffer position to viewport position
+    const viewportStartRow = start[1] - terminal.buffer.ydisp;
+    const viewportEndRow = end[1] - terminal.buffer.ydisp;
+    const viewportCappedStartRow = Math.max(viewportStartRow, 0);
+    const viewportCappedEndRow = Math.min(viewportEndRow, terminal.rows - 1);
+
+    // No need to draw the selection
+    if (viewportCappedStartRow >= terminal.rows || viewportCappedEndRow < 0) {
+      this._model.clearSelection();
+      return;
+    }
+
+    this._model.selection.hasSelection = true;
+    this._model.selection.viewportStartRow = viewportStartRow;
+    this._model.selection.viewportEndRow = viewportEndRow;
+    this._model.selection.viewportCappedStartRow = viewportCappedStartRow;
+    this._model.selection.viewportCappedEndRow = viewportCappedEndRow;
+    this._model.selection.startCol = start[0];
+    this._model.selection.endCol = end[0];
+  }
+
+  /**
+   * Recalculates the character and canvas dimensions.
+   */
+  private _updateDimensions(devicePixelRatio: number = window.devicePixelRatio): void {
+    // Perform a new measure if the CharMeasure dimensions are not yet available
+    if (!this._terminal.charMeasure.width || !this._terminal.charMeasure.height) {
+      return;
+    }
+
+    // Calculate the scaled character width. Width is floored as it must be
+    // drawn to an integer grid in order for the CharAtlas "stamps" to not be
+    // blurry. When text is drawn to the grid not using the CharAtlas, it is
+    // clipped to ensure there is no overlap with the next cell.
+
+    // NOTE: ceil fixes sometime, floor does others :s
+
+    this.dimensions.scaledCharWidth = Math.floor(this._terminal.charMeasure.width * devicePixelRatio);
+
+    // Calculate the scaled character height. Height is ceiled in case
+    // devicePixelRatio is a floating point number in order to ensure there is
+    // enough space to draw the character to the cell.
+    this.dimensions.scaledCharHeight = Math.ceil(this._terminal.charMeasure.height * devicePixelRatio);
+
+    // Calculate the scaled cell height, if lineHeight is not 1 then the value
+    // will be floored because since lineHeight can never be lower then 1, there
+    // is a guarentee that the scaled line height will always be larger than
+    // scaled char height.
+    this.dimensions.scaledCellHeight = Math.floor(this.dimensions.scaledCharHeight * this._terminal.options.lineHeight);
+
+    // Calculate the y coordinate within a cell that text should draw from in
+    // order to draw in the center of a cell.
+    this.dimensions.scaledCharTop = this._terminal.options.lineHeight === 1 ? 0 : Math.round((this.dimensions.scaledCellHeight - this.dimensions.scaledCharHeight) / 2);
+
+    // Calculate the scaled cell width, taking the letterSpacing into account.
+    this.dimensions.scaledCellWidth = this.dimensions.scaledCharWidth + Math.round(this._terminal.options.letterSpacing);
+
+    // Calculate the x coordinate with a cell that text should draw from in
+    // order to draw in the center of a cell.
+    this.dimensions.scaledCharLeft = Math.floor(this._terminal.options.letterSpacing / 2);
+
+    // Recalculate the canvas dimensions; scaled* define the actual number of
+    // pixel in the canvas
+    this.dimensions.scaledCanvasHeight = this._terminal.rows * this.dimensions.scaledCellHeight;
+    this.dimensions.scaledCanvasWidth = this._terminal.cols * this.dimensions.scaledCellWidth;
+
+    // The the size of the canvas on the page. It's very important that this
+    // rounds to nearest integer and not ceils as browsers often set
+    // window.devicePixelRatio as something like 1.100000023841858, when it's
+    // actually 1.1. Ceiling causes blurriness as the backing canvas image is 1
+    // pixel too large for the canvas element size.
+    this.dimensions.canvasHeight = Math.round(this.dimensions.scaledCanvasHeight / devicePixelRatio);
+    this.dimensions.canvasWidth = Math.round(this.dimensions.scaledCanvasWidth / devicePixelRatio);
+
+    // this.dimensions.scaledCanvasHeight = this.dimensions.canvasHeight * devicePixelRatio;
+    // this.dimensions.scaledCanvasWidth = this.dimensions.canvasWidth * devicePixelRatio;
+
+    // Get the _actual_ dimensions of an individual cell. This needs to be
+    // derived from the canvasWidth/Height calculated above which takes into
+    // account window.devicePixelRatio. CharMeasure.width/height by itself is
+    // insufficient when the page is not at 100% zoom level as CharMeasure is
+    // measured in CSS pixels, but the actual char size on the canvas can
+    // differ.
+    // this.dimensions.actualCellHeight = this.dimensions.canvasHeight / this._terminal.rows;
+    // this.dimensions.actualCellWidth = this.dimensions.canvasWidth / this._terminal.cols;
+
+    // This fixes 110% and 125%, not 150% or 175% though
+    this.dimensions.actualCellHeight = this.dimensions.scaledCellHeight / devicePixelRatio;
+    this.dimensions.actualCellWidth = this.dimensions.scaledCellWidth / devicePixelRatio;
+  }
+}

src/renderer/webgl/WebglUtils.ts

@@ -0,0 +1,51 @@
+/**
+ * Copyright (c) 2018 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+/**
+ * A matrix that when multiplies will translate 0-1 coordinates (left to right,
+ * top to bottom) to clip space.
+ */
+export const PROJECTION_MATRIX = new Float32Array([
+  2, 0, 0, 0,
+  0, -2, 0, 0,
+  0, 0, 1, 0,
+  -1, 1, 0, 1
+]);
+
+export function createProgram(gl: WebGLRenderingContext, vertexSource: string, fragmentSource: string): WebGLProgram | undefined {
+  const program = gl.createProgram();
+  gl.attachShader(program, createShader(gl, gl.VERTEX_SHADER, vertexSource));
+  gl.attachShader(program, createShader(gl, gl.FRAGMENT_SHADER, fragmentSource));
+  gl.linkProgram(program);
+  const success = gl.getProgramParameter(program, gl.LINK_STATUS);
+  if (success) {
+    return program;
+  }
+
+  console.log(gl.getProgramInfoLog(program));
+  gl.deleteProgram(program);
+}
+
+export function createShader(gl: WebGLRenderingContext, type: number, source: string): WebGLShader | undefined {
+  const shader = gl.createShader(type);
+  gl.shaderSource(shader, source);
+  gl.compileShader(shader);
+  const success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
+  if (success) {
+    return shader;
+  }
+
+  console.log(gl.getShaderInfoLog(shader));
+  gl.deleteShader(shader);
+}
+
+export function expandFloat32Array(source: Float32Array, max: number): Float32Array {
+  const newLength = Math.min(source.length * 2, max);
+  const newArray = new Float32Array(newLength);
+  for (let i = 0; i < source.length; i++) {
+    newArray[i] = source[i];
+  }
+  return newArray;
+}

src/shared/atlas/Types.ts

@@ -9,7 +9,7 @@ import { IColorSet } from '../Types';
 export const CHAR_ATLAS_CELL_SPACING = 1;
 
 export interface ICharAtlasConfig {
-  type: 'none' | 'static' | 'dynamic';
+  type: 'none' | 'static' | 'dynamic' | 'webgl';
   devicePixelRatio: number;
   fontSize: number;
   fontFamily: string;

typings/xterm.d.ts

@@ -18,7 +18,7 @@ declare module 'xterm' {
   /**
    * A string representing a renderer type.
    */
-  export type RendererType = 'dom' | 'canvas';
+  export type RendererType = 'dom' | 'canvas' | 'webgl';
 
   /**
    * An object containing start up options for the terminal.
@@ -99,7 +99,7 @@ declare module 'xterm' {
      * Currently defaults to 'static'. This option may be removed in the future. If it is, passed
      * parameters will be ignored.
      */
-    experimentalCharAtlas?: 'none' | 'static' | 'dynamic';
+    experimentalCharAtlas?: 'none' | 'static' | 'dynamic' | 'webgl';
 
     /**
      * (EXPERIMENTAL) Defines which implementation to use for buffer lines.
@@ -213,7 +213,7 @@ declare module 'xterm' {
     cursor?: string,
     /** The accent color of the cursor (used as the foreground color for a block cursor) */
     cursorAccent?: string,
-    /** The selection color (can be transparent) */
+    /** The selection background color (can be transparent) */
     selection?: string,
     /** ANSI black (eg. `\x1b[30m`) */
     black?: string,