FINALLY fix blurry canvas/webgl renderer issues due to device pixel rounding errors 🎉

addons/xterm-addon-canvas/src/BaseRenderLayer.ts

@@ -49,6 +49,8 @@ export abstract class BaseRenderLayer implements IRenderLayer {
     italic: false
   };
 
+  public get canvas(): HTMLCanvasElement { return this._canvas; }
+
   constructor(
     private _container: HTMLElement,
     id: string,

addons/xterm-addon-canvas/src/CanvasRenderer.ts

@@ -15,6 +15,7 @@ import { ICharSizeService } from 'browser/services/Services';
 import { IBufferService, IOptionsService, IInstantiationService } from 'common/services/Services';
 import { removeTerminalFromCache } from './atlas/CharAtlasCache';
 import { EventEmitter, IEvent } from 'common/EventEmitter';
+import { observeDevicePixelDimensions } from 'browser/renderer/DevicePixelObserver';
 
 let nextRendererId = 1;
 
@@ -62,6 +63,9 @@ export class CanvasRenderer extends Disposable implements IRenderer {
     };
     this._devicePixelRatio = window.devicePixelRatio;
     this._updateDimensions();
+
+    this.register(observeDevicePixelDimensions(this._renderLayers[0].canvas, (w, h) => this._setCanvasDevicePixelDimensions(w, h)));
+
     this.onOptionsChanged();
   }
 
@@ -167,53 +171,32 @@ export class CanvasRenderer extends Disposable implements IRenderer {
       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.
+    // See the WebGL renderer for an explanation of this section.
     this.dimensions.scaledCharWidth = Math.floor(this._charSizeService.width * window.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._charSizeService.height * window.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._optionsService.rawOptions.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._optionsService.rawOptions.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._optionsService.rawOptions.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._optionsService.rawOptions.letterSpacing / 2);
-
-    // Recalculate the canvas dimensions; scaled* define the actual number of
-    // pixel in the canvas
     this.dimensions.scaledCanvasHeight = this._bufferService.rows * this.dimensions.scaledCellHeight;
     this.dimensions.scaledCanvasWidth = this._bufferService.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 / window.devicePixelRatio);
     this.dimensions.canvasWidth = Math.round(this.dimensions.scaledCanvasWidth / window.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. ICharSizeService.width/height by itself
-    // is insufficient when the page is not at 100% zoom level as it's measured
-    // in CSS pixels, but the actual char size on the canvas can differ.
     this.dimensions.actualCellHeight = this.dimensions.canvasHeight / this._bufferService.rows;
     this.dimensions.actualCellWidth = this.dimensions.canvasWidth / this._bufferService.cols;
   }
+
+  private _setCanvasDevicePixelDimensions(width: number, height: number): void {
+    this.dimensions.scaledCanvasHeight = height;
+    this.dimensions.scaledCanvasWidth = width;
+    // Resize all render layers
+    for (const l of this._renderLayers) {
+      l.resize(this.dimensions);
+    }
+    this._requestRedrawViewport();
+  }
+
+  private _requestRedrawViewport(): void {
+    this._onRequestRedraw.fire({ start: 0, end: this._bufferService.rows - 1 });
+  }
 }

addons/xterm-addon-canvas/src/Types.d.ts

@@ -57,6 +57,8 @@ export interface IRenderer extends IDisposable {
 }
 
 export interface IRenderLayer extends IDisposable {
+  readonly canvas: HTMLCanvasElement;
+
   /**
    * Called when the terminal loses focus.
    */

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

@@ -11,11 +11,12 @@ import { WebglCharAtlas } from './atlas/WebglCharAtlas';
 import { RectangleRenderer } from './RectangleRenderer';
 import { IWebGL2RenderingContext } from './Types';
 import { RenderModel, COMBINED_CHAR_BIT_MASK, RENDER_MODEL_BG_OFFSET, RENDER_MODEL_FG_OFFSET, RENDER_MODEL_INDICIES_PER_CELL } from './RenderModel';
-import { Disposable } from 'common/Lifecycle';
+import { Disposable, toDisposable } from 'common/Lifecycle';
 import { Attributes, Content, FgFlags, NULL_CELL_CHAR, NULL_CELL_CODE } from 'common/buffer/Constants';
 import { Terminal, IEvent } from 'xterm';
 import { IRenderLayer } from './renderLayer/Types';
 import { IRenderDimensions, IRenderer, IRequestRedrawEvent } from 'browser/renderer/Types';
+import { observeDevicePixelDimensions } from 'browser/renderer/DevicePixelObserver';
 import { ITerminal, IColorSet } from 'browser/Types';
 import { EventEmitter } from 'common/EventEmitter';
 import { CellData } from 'common/buffer/CellData';
@@ -95,6 +96,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
     }
 
     this.register(addDisposableDomListener(this._canvas, 'webglcontextlost', (e) => { this._onContextLoss.fire(e); }));
+    this.register(observeDevicePixelDimensions(this._canvas, (w, h) => this._setCanvasDevicePixelDimensions(w, h)));
 
     this._core.screenElement!.appendChild(this._canvas);
 
@@ -517,67 +519,63 @@ export class WebglRenderer extends Disposable implements IRenderer {
       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
-
+    // Calculate the scaled character width. Width is floored as it must be drawn to an integer grid
+    // in order for the char atlas glyphs to not be blurry.
     this.dimensions.scaledCharWidth = Math.floor((this._core as any)._charSizeService.width * this._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.
+    // 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._core as any)._charSizeService.height * this._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.
+    // Calculate the scaled cell height, if lineHeight is _not_ 1, the resulting value will be
+    // floored since lineHeight can never be lower then 1, this guarentees the scaled cell 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.
+    // Calculate the y offset within a cell that glyph should draw at in order for it to be centered
+    // correctly within the 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.
+    // Calculate the x offset with a cell that text should draw from in order for it to be centered
+    // correctly within the 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
+    // Recalculate the canvas dimensions, the scaled dimensions 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.
+    // The the size of the canvas on the page. It's important that this rounds to nearest integer
+    // and not ceils as browsers often have floating point precision issues where
+    // `window.devicePixelRatio` ends up being something like `1.100000023841858` for example, when
+    // it's actually 1.1. Ceiling may 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 / this._devicePixelRatio);
     this.dimensions.canvasWidth = Math.round(this.dimensions.scaledCanvasWidth / this._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
+    // Get the CSS dimensions of an individual cell. This needs to be derived from the calculated
+    // device pixel canvas value above. 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.scaledCellHeight / this._devicePixelRatio;
     this.dimensions.actualCellWidth = this.dimensions.scaledCellWidth / this._devicePixelRatio;
   }
 
+  private _setCanvasDevicePixelDimensions(width: number, height: number): void {
+    if (this.dimensions.scaledCanvasWidth === width && this.dimensions.scaledCanvasHeight === height) {
+      return;
+    }
+    this.dimensions.scaledCanvasWidth = width;
+    this.dimensions.scaledCanvasHeight = height;
+    this._canvas.width = width;
+    this._canvas.height = height;
+    this._requestRedrawViewport();
+  }
+
   private _requestRedrawViewport(): void {
     this._onRequestRedraw.fire({ start: 0, end: this._terminal.rows - 1 });
   }

package.json

@@ -79,8 +79,8 @@
     "playwright": "^1.22.1",
     "source-map-loader": "^3.0.0",
     "source-map-support": "^0.5.20",
-    "ts-loader": "^9.1.2",
-    "typescript": "^4.4.4",
+    "ts-loader": "^9.3.1",
+    "typescript": "4.7",
     "utf8": "^3.0.0",
     "webpack": "^5.61.0",
     "webpack-cli": "^4.9.1",

src/browser/renderer/DevicePixelObserver.ts

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) 2022 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { toDisposable } from 'common/Lifecycle';
+import { IDisposable } from 'common/Types';
+
+export function observeDevicePixelDimensions(element: HTMLElement, callback: (deviceWidth: number, deviceHeight: number) => void): IDisposable {
+  // Observe any resizes to the element and extract the actual pixel size of the element if the
+  // devicePixelContentBoxSize API is supported. This allows correcting rounding errors when
+  // converting between CSS pixels and device pixels which causes blurry rendering when device
+  // pixel ratio is not a round number.
+  let observer: ResizeObserver | undefined = new ResizeObserver((entries) => {
+    const entry = entries.find((entry) => entry.target === element);
+    if (!entry) {
+      return;
+    }
+
+    // Disconnect if devicePixelContentBoxSize isn't supported by the browser
+    if (!('devicePixelContentBoxSize' in entry)) {
+      observer?.disconnect();
+      observer = undefined;
+      return;
+    }
+
+    callback(
+      entry.devicePixelContentBoxSize[0].inlineSize,
+      entry.devicePixelContentBoxSize[0].blockSize
+    );
+  });
+  observer.observe(element, { box: ['device-pixel-content-box'] } as any);
+  return toDisposable(() => observer?.disconnect());
+}

yarn.lock

@@ -3760,10 +3760,10 @@ tr46@^3.0.0:
   dependencies:
     punycode "^2.1.1"
 
-ts-loader@^9.1.2:
-  version "9.2.6"
-  resolved "https://registry.yarnpkg.com/ts-loader/-/ts-loader-9.2.6.tgz#9937c4dd0a1e3dbbb5e433f8102a6601c6615d74"
-  integrity sha512-QMTC4UFzHmu9wU2VHZEmWWE9cUajjfcdcws+Gh7FhiO+Dy0RnR1bNz0YCHqhI0yRowCE9arVnNxYHqELOy9Hjw==
+ts-loader@^9.3.1:
+  version "9.3.1"
+  resolved "https://registry.yarnpkg.com/ts-loader/-/ts-loader-9.3.1.tgz#fe25cca56e3e71c1087fe48dc67f4df8c59b22d4"
+  integrity sha512-OkyShkcZTsTwyS3Kt7a4rsT/t2qvEVQuKCTg4LJmpj9fhFR7ukGdZwV6Qq3tRUkqcXtfGpPR7+hFKHCG/0d3Lw==
   dependencies:
     chalk "^4.1.0"
     enhanced-resolve "^5.0.0"
@@ -3831,16 +3831,16 @@ typedarray-to-buffer@^3.1.5:
   dependencies:
     is-typedarray "^1.0.0"
 
+typescript@4.7:
+  version "4.7.4"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.7.4.tgz#1a88596d1cf47d59507a1bcdfb5b9dfe4d488235"
+  integrity sha512-C0WQT0gezHuw6AdY1M2jxUO83Rjf0HP7Sk1DtXj6j1EwkQNZrHAg2XPWlq62oqEhYvONq5pkC2Y9oPljWToLmQ==
+
 typescript@^4.2.3:
   version "4.6.4"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.6.4.tgz#caa78bbc3a59e6a5c510d35703f6a09877ce45e9"
   integrity sha512-9ia/jWHIEbo49HfjrLGfKbZSuWo9iTMwXO+Ca3pRsSpbsMbc7/IU8NKdCZVRRBafVPGnoJeFL76ZOAA84I9fEg==
 
-typescript@^4.4.4:
-  version "4.4.4"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.4.4.tgz#2cd01a1a1f160704d3101fd5a58ff0f9fcb8030c"
-  integrity sha512-DqGhF5IKoBl8WNf8C1gu8q0xZSInh9j1kJJMqT3a94w1JzVaBU4EXOSMrz9yDqMT0xt3selp83fuFMQ0uzv6qA==
-
 unbox-primitive@^1.0.0:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/unbox-primitive/-/unbox-primitive-1.0.1.tgz#085e215625ec3162574dc8859abee78a59b14471"