Object pool, correct merging of zones

demo/client.ts

@@ -556,8 +556,8 @@ function loadTest() {
 function addDecoration() {
   term.options['overviewRulerWidth'] = 15;
   const marker = term.addMarker(1);
-  const decoration = term.registerDecoration({ marker, overviewRulerOptions: { color: '#ef2929'} });
-  decoration.onRender((e) => e.style.backgroundColor = '#ef2929');
+  const decoration = term.registerDecoration({ marker, overviewRulerOptions: { color: '#ef292980', position: 'left' } });
+  decoration.onRender((e) => e.style.backgroundColor = '#ef292980');
 }
 
 function addOverviewRuler() {

src/browser/Decorations/ColorZoneStore.ts

@@ -26,7 +26,12 @@ export interface IColorZone {
 
 export class ColorZoneStore implements IColorZoneStore {
   private _zones: IColorZone[] = [];
-  public get zones(): IColorZone[] { return this._zones; }
+
+  // The zone pool is used to keep zone objects from being freed between clearing the color zone
+  // store and fetching the zones. This helps reduce GC pressure since the color zones are
+  // accumulated on potentially every scroll event.
+  private _zonePool: IColorZone[] = [];
+  private _zonePoolIndex = 0;
 
   private _linePadding: { [position: string]: number } = {
     full: 0,
@@ -35,8 +40,15 @@ export class ColorZoneStore implements IColorZoneStore {
     right: 0
   };
 
+  public get zones(): IColorZone[] {
+    // Trim the zone pool to free unused memory
+    this._zonePool.length = Math.min(this._zonePool.length, this._zones.length);
+    return this._zones;
+  }
+
   public clear(): void {
     this._zones.length = 0;
+    this._zonePoolIndex = 0;
   }
 
   public addDecoration(decoration: IInternalDecoration): void {
@@ -50,22 +62,33 @@ export class ColorZoneStore implements IColorZoneStore {
           return;
         }
         if (this._lineAdjacentToZone(z, decoration.marker.line, decoration.options.overviewRulerOptions.position)) {
+          console.log('add line to zone');
           this._addLineToZone(z, decoration.marker.line);
           return;
         }
       }
     }
-    // TODO: Track zones in an object pool to reduce GC
+    // Create using zone pool if possible
+    if (this._zonePoolIndex < this._zonePool.length) {
+      this._zonePool[this._zonePoolIndex].color = decoration.options.overviewRulerOptions.color;
+      this._zonePool[this._zonePoolIndex].position = decoration.options.overviewRulerOptions.position;
+      this._zonePool[this._zonePoolIndex].startBufferLine = decoration.marker.line;
+      this._zonePool[this._zonePoolIndex].endBufferLine = decoration.marker.line;
+      this._zones.push(this._zonePool[this._zonePoolIndex++]);
+      return;
+    }
+    // Create
     this._zones.push({
       color: decoration.options.overviewRulerOptions.color,
       position: decoration.options.overviewRulerOptions.position,
       startBufferLine: decoration.marker.line,
       endBufferLine: decoration.marker.line
     });
+    this._zonePool.push(this._zones[this._zones.length - 1]);
+    this._zonePoolIndex++;
   }
 
   public setPadding(padding: { [position: string]: number }): void {
-    console.log('padding', padding);
     this._linePadding = padding;
   }
 
@@ -78,8 +101,8 @@ export class ColorZoneStore implements IColorZoneStore {
 
   private _lineAdjacentToZone(zone: IColorZone, line: number, position: IColorZone['position']): boolean {
     return (
-      (line >= zone.startBufferLine - this._linePadding[position || 'full'] * 2) &&
-      (line <= zone.endBufferLine + this._linePadding[position || 'full'] * 2)
+      (line >= zone.startBufferLine - this._linePadding[position || 'full']) &&
+      (line <= zone.endBufferLine + this._linePadding[position || 'full'])
     );
   }
 

src/browser/Decorations/OverviewRulerRenderer.ts

@@ -150,10 +150,10 @@ export class OverviewRulerRenderer extends Disposable {
 
   private _refreshColorZonePadding(): void {
     this._colorZoneStore.setPadding({
-      full: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * (drawHeight.full / 2)),
-      left: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * (drawHeight.left / 2)),
-      center: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * (drawHeight.center / 2)),
-      right: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * (drawHeight.right / 2))
+      full: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * drawHeight.full),
+      left: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * drawHeight.left),
+      center: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * drawHeight.center),
+      right: Math.floor(this._bufferService.buffers.active.lines.length / (this._canvas.height - 1) * drawHeight.right)
     });
     this._lastKnownBufferLength = this._bufferService.buffers.normal.lines.length;
   }
@@ -196,7 +196,6 @@ export class OverviewRulerRenderer extends Disposable {
     // TODO: Is _decorationElements needed?
 
     this._ctx.fillStyle = zone.color;
-    console.log('zone height', drawHeight[zone.position || 'full']);
     this._ctx.fillRect(
       /* x */ drawX[zone.position || 'full'],
       /* y */ Math.round(