Merge pull request #4346 from Tyriar/4314_2

Clamp start and end in render service to ensure they're valid

addons/xterm-addon-webgl/src/WebglRenderer.ts

@@ -352,7 +352,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
     let lastBg: number;
     let y: number;
     let row: number;
-    let line: IBufferLine | undefined;
+    let line: IBufferLine;
     let joinedRanges: [number, number][];
     let isJoined: boolean;
     let lastCharX: number;
@@ -365,10 +365,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
 
     for (y = start; y <= end; y++) {
       row = y + terminal.buffer.ydisp;
-      line = terminal.buffer.lines.get(row);
-      if (!line) {
-        break;
-      }
+      line = terminal.buffer.lines.get(row)!;
       this._model.lineLengths[y] = 0;
       joinedRanges = this._characterJoinerService.getJoinedCharacters(row);
       for (x = 0; x < terminal.cols; x++) {

src/browser/services/RenderService.ts

@@ -152,6 +152,14 @@ export class RenderService extends Disposable implements IRenderService {
     if (!this._renderer) {
       return;
     }
+
+    // Since this is debounced, a resize event could have happened between the time a refresh was
+    // requested and when this triggers. Clamp the values of start and end to ensure they're valid
+    // given the current viewport state.
+    start = Math.min(start, this._rowCount - 1);
+    end = Math.min(end, this._rowCount - 1);
+
+    // Render
     this._renderer.renderRows(start, end);
 
     // Update selection if needed