Introduce opt-in glyph scaling to achieve GB18030 compliance

addons/addon-canvas/src/BaseRenderLayer.ts

@@ -8,7 +8,7 @@ import { CellColorResolver } from 'browser/renderer/shared/CellColorResolver';
 import { acquireTextureAtlas } from 'browser/renderer/shared/CharAtlasCache';
 import { TEXT_BASELINE } from 'browser/renderer/shared/Constants';
 import { tryDrawCustomChar } from 'browser/renderer/shared/CustomGlyphs';
-import { throwIfFalsy } from 'browser/renderer/shared/RendererUtils';
+import { isEmoji, throwIfFalsy } from 'browser/renderer/shared/RendererUtils';
 import { createSelectionRenderModel } from 'browser/renderer/shared/SelectionRenderModel';
 import { IRasterizedGlyph, IRenderDimensions, ISelectionRenderModel, ITextureAtlas } from 'browser/renderer/shared/Types';
 import { ICoreBrowserService, IThemeService } from 'browser/services/Services';
@@ -365,6 +365,8 @@ export abstract class BaseRenderLayer extends Disposable implements IRenderLayer
    */
   protected _drawChars(cell: ICellData, x: number, y: number): void {
     const chars = cell.getChars();
+    const code = cell.getCode();
+    const width = cell.getWidth();
     this._cellColorResolver.resolve(cell, x, this._bufferService.buffer.ydisp + y, this._deviceCellWidth);
 
     if (!this._charAtlas) {
@@ -400,6 +402,23 @@ export abstract class BaseRenderLayer extends Disposable implements IRenderLayer
       this._bitmapGenerator[glyph.texturePage]!.refresh();
       this._bitmapGenerator[glyph.texturePage]!.version = this._charAtlas.pages[glyph.texturePage].version;
     }
+
+    // Reduce scale horizontally for wide glyphs printed in cells that would overlap with the
+    // following cell (ie. the width is not 2).
+    let renderWidth = glyph.size.x;
+    if (this._optionsService.rawOptions.rescaleOverlappingGlyphs) {
+      if (
+        // Is single cell width
+        width === 1 &&
+        // Glyph exceeds cell bounds, + 1 to avoid hurting readability
+        glyph.size.x > this._deviceCellWidth + 1 &&
+        // Never rescale emoji
+        code && !isEmoji(code)
+      ) {
+        renderWidth = this._deviceCellWidth - 1; // - 1 to improve readability
+      }
+    }
+
     this._ctx.drawImage(
       this._bitmapGenerator[glyph.texturePage]?.bitmap || this._charAtlas!.pages[glyph.texturePage].canvas,
       glyph.texturePosition.x,
@@ -408,7 +427,7 @@ export abstract class BaseRenderLayer extends Disposable implements IRenderLayer
       glyph.size.y,
       x * this._deviceCellWidth + this._deviceCharLeft - glyph.offset.x,
       y * this._deviceCellHeight + this._deviceCharTop - glyph.offset.y,
-      glyph.size.x,
+      renderWidth,
       glyph.size.y
     );
     this._ctx.restore();

addons/addon-webgl/src/GlyphRenderer.ts

@@ -3,14 +3,15 @@
  * @license MIT
  */
 
-import { throwIfFalsy } from 'browser/renderer/shared/RendererUtils';
+import { isEmoji, throwIfFalsy } from 'browser/renderer/shared/RendererUtils';
 import { TextureAtlas } from 'browser/renderer/shared/TextureAtlas';
 import { IRasterizedGlyph, IRenderDimensions, ITextureAtlas } from 'browser/renderer/shared/Types';
 import { NULL_CELL_CODE } from 'common/buffer/Constants';
 import { Disposable, toDisposable } from 'common/Lifecycle';
 import { Terminal } from '@xterm/xterm';
 import { IRenderModel, IWebGL2RenderingContext, IWebGLVertexArrayObject } from './Types';
 import { createProgram, GLTexture, PROJECTION_MATRIX } from './WebglUtils';
+import type { IOptionsService } from 'common/services/Services';
 
 interface IVertices {
   attributes: Float32Array;
@@ -111,7 +112,8 @@ export class GlyphRenderer extends Disposable {
   constructor(
     private readonly _terminal: Terminal,
     private readonly _gl: IWebGL2RenderingContext,
-    private _dimensions: IRenderDimensions
+    private _dimensions: IRenderDimensions,
+    private readonly _optionsService: IOptionsService
   ) {
     super();
 
@@ -212,15 +214,15 @@ export class GlyphRenderer extends Disposable {
     return this._atlas ? this._atlas.beginFrame() : true;
   }
 
-  public updateCell(x: number, y: number, code: number, bg: number, fg: number, ext: number, chars: string, lastBg: number): void {
+  public updateCell(x: number, y: number, code: number, bg: number, fg: number, ext: number, chars: string, width: number, lastBg: number): void {
     // Since this function is called for every cell (`rows*cols`), it must be very optimized. It
     // should not instantiate any variables unless a new glyph is drawn to the cache where the
     // slight slowdown is acceptable for the developer ergonomics provided as it's a once of for
     // each glyph.
-    this._updateCell(this._vertices.attributes, x, y, code, bg, fg, ext, chars, lastBg);
+    this._updateCell(this._vertices.attributes, x, y, code, bg, fg, ext, chars, width, lastBg);
   }
 
-  private _updateCell(array: Float32Array, x: number, y: number, code: number | undefined, bg: number, fg: number, ext: number, chars: string, lastBg: number): void {
+  private _updateCell(array: Float32Array, x: number, y: number, code: number | undefined, bg: number, fg: number, ext: number, chars: string, width: number, lastBg: number): void {
     $i = (y * this._terminal.cols + x) * INDICES_PER_CELL;
 
     // Exit early if this is a null character, allow space character to continue as it may have
@@ -275,6 +277,21 @@ export class GlyphRenderer extends Disposable {
       array[$i + 8] = $glyph.sizeClipSpace.y;
     }
     // a_cellpos only changes on resize
+
+    // Reduce scale horizontally for wide glyphs printed in cells that would overlap with the
+    // following cell (ie. the width is not 2).
+    if (this._optionsService.rawOptions.rescaleOverlappingGlyphs) {
+      if (
+        // Is single cell width
+        width === 1 &&
+        // Glyph exceeds cell bounds, + 1 to avoid hurting readability
+        $glyph.size.x > this._dimensions.device.cell.width + 1 &&
+        // Never rescale emoji
+        code && !isEmoji(code)
+      ) {
+        array[$i + 2] = (this._dimensions.device.cell.width - 1) / this._dimensions.device.canvas.width; // - 1 to improve readability
+      }
+    }
   }
 
   public clear(): void {

addons/addon-webgl/src/WebglRenderer.ts

@@ -36,7 +36,8 @@ export class WebglRenderer extends Disposable implements IRenderer {
   private _observerDisposable = this.register(new MutableDisposable());
 
   private _model: RenderModel = new RenderModel();
-  private _workCell: CellData = new CellData();
+  private _workCell: ICellData = new CellData();
+  private _workCell2: ICellData = new CellData();
   private _cellColorResolver: CellColorResolver;
 
   private _canvas: HTMLCanvasElement;
@@ -245,7 +246,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
    */
   private _initializeWebGLState(): [RectangleRenderer, GlyphRenderer] {
     this._rectangleRenderer.value = new RectangleRenderer(this._terminal, this._gl, this.dimensions, this._themeService);
-    this._glyphRenderer.value = new GlyphRenderer(this._terminal, this._gl, this.dimensions);
+    this._glyphRenderer.value = new GlyphRenderer(this._terminal, this._gl, this.dimensions, this._optionsService);
 
     // Update dimensions and acquire char atlas
     this.handleCharSizeChanged();
@@ -388,6 +389,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
     let range: [number, number];
     let chars: string;
     let code: number;
+    let width: number;
     let i: number;
     let x: number;
     let j: number;
@@ -500,7 +502,8 @@ export class WebglRenderer extends Disposable implements IRenderer {
         this._model.cells[i + RENDER_MODEL_FG_OFFSET] = this._cellColorResolver.result.fg;
         this._model.cells[i + RENDER_MODEL_EXT_OFFSET] = this._cellColorResolver.result.ext;
 
-        this._glyphRenderer.value!.updateCell(x, y, code, this._cellColorResolver.result.bg, this._cellColorResolver.result.fg, this._cellColorResolver.result.ext, chars, lastBg);
+        width = cell.getWidth();
+        this._glyphRenderer.value!.updateCell(x, y, code, this._cellColorResolver.result.bg, this._cellColorResolver.result.fg, this._cellColorResolver.result.ext, chars, width, lastBg);
 
         if (isJoined) {
           // Restore work cell
@@ -509,7 +512,7 @@ export class WebglRenderer extends Disposable implements IRenderer {
           // Null out non-first cells
           for (x++; x < lastCharX; x++) {
             j = ((y * terminal.cols) + x) * RENDER_MODEL_INDICIES_PER_CELL;
-            this._glyphRenderer.value!.updateCell(x, y, NULL_CELL_CODE, 0, 0, 0, NULL_CELL_CHAR, 0);
+            this._glyphRenderer.value!.updateCell(x, y, NULL_CELL_CODE, 0, 0, 0, NULL_CELL_CHAR, 0, 0);
             this._model.cells[j] = NULL_CELL_CODE;
             this._model.cells[j + RENDER_MODEL_BG_OFFSET] = this._cellColorResolver.result.bg;
             this._model.cells[j + RENDER_MODEL_FG_OFFSET] = this._cellColorResolver.result.fg;

src/browser/renderer/shared/RendererUtils.ts

@@ -27,6 +27,19 @@ function isBoxOrBlockGlyph(codepoint: number): boolean {
   return 0x2500 <= codepoint && codepoint <= 0x259F;
 }
 
+export function isEmoji(codepoint: number): boolean {
+  return (
+    codepoint >= 0x1F600 && codepoint <= 0x1F64F || // Emoticons
+    codepoint >= 0x1F300 && codepoint <= 0x1F5FF ||  // Misc Symbols and Pictographs
+    codepoint >= 0x1F680 && codepoint <= 0x1F6FF ||  // Transport and Map
+    codepoint >= 0x2600 && codepoint <= 0x26FF ||    // Misc symbols
+    codepoint >= 0x2700 && codepoint <= 0x27BF ||    // Dingbats
+    codepoint >= 0xFE00 && codepoint <= 0xFE0F ||    // Variation Selectors
+    codepoint >= 0x1F900 && codepoint <= 0x1F9FF ||  // Supplemental Symbols and Pictographs
+    codepoint >= 0x1F1E6 && codepoint <= 0x1F1FF
+  );
+}
+
 export function treatGlyphAsBackgroundColor(codepoint: number): boolean {
   return isPowerlineGlyph(codepoint) || isBoxOrBlockGlyph(codepoint);
 }

src/browser/services/RenderService.ts

@@ -87,7 +87,8 @@ export class RenderService extends Disposable implements IRenderService {
       'fontSize',
       'fontWeight',
       'fontWeightBold',
-      'minimumContrastRatio'
+      'minimumContrastRatio',
+      'rescaleOverlappingGlyphs'
     ], () => {
       this.clear();
       this.handleResize(bufferService.cols, bufferService.rows);

src/common/services/OptionsService.ts

@@ -44,6 +44,7 @@ export const DEFAULT_OPTIONS: Readonly<Required<ITerminalOptions>> = {
   allowTransparency: false,
   tabStopWidth: 8,
   theme: {},
+  rescaleOverlappingGlyphs: false,
   rightClickSelectsWord: isMac,
   windowOptions: {},
   windowsMode: false,

src/common/services/Services.ts

@@ -234,6 +234,7 @@ export interface ITerminalOptions {
   macOptionIsMeta?: boolean;
   macOptionClickForcesSelection?: boolean;
   minimumContrastRatio?: number;
+  rescaleOverlappingGlyphs?: boolean;
   rightClickSelectsWord?: boolean;
   rows?: number;
   screenReaderMode?: boolean;

typings/xterm-headless.d.ts

@@ -140,6 +140,17 @@ declare module '@xterm/headless' {
      */
     minimumContrastRatio?: number;
 
+    /**
+     * Whether to rescale glyphs horizontally that are a single cell wide but
+     * have glyphs that would overlap following cell(s). This typically happens
+     * for ambiguous width characters (eg. the roman numeral characters U+2160+)
+     * which aren't featured in monospace fonts. Emoji glyphs are never
+     * rescaled. This is an important feature for achieving GB18030 compliance.
+     *
+     * Note that this doesn't work with the DOM renderer. The default is false.
+     */
+    rescaleOverlappingGlyphs?: boolean;
+
     /**
      * Whether to select the word under the cursor on right click, this is
      * standard behavior in a lot of macOS applications.

typings/xterm.d.ts

@@ -209,6 +209,17 @@ declare module '@xterm/xterm' {
      */
     minimumContrastRatio?: number;
 
+    /**
+     * Whether to rescale glyphs horizontally that are a single cell wide but
+     * have glyphs that would overlap following cell(s). This typically happens
+     * for ambiguous width characters (eg. the roman numeral characters U+2160+)
+     * which aren't featured in monospace fonts. Emoji glyphs are never
+     * rescaled. This is an important feature for achieving GB18030 compliance.
+     *
+     * Note that this doesn't work with the DOM renderer. The default is false.
+     */
+    rescaleOverlappingGlyphs?: boolean;
+
     /**
      * Whether to select the word under the cursor on right click, this is
      * standard behavior in a lot of macOS applications.