preserve zero advance glyphs in latest Noto Sans Arabic

Author: chearon

src/layout-text.ts

@@ -43,7 +43,7 @@ function isWsPreserved(whiteSpace: WhiteSpace) {
   return whiteSpace === 'pre' || whiteSpace === 'pre-wrap';
 }
 
-function isSpaceOrTabOrNewline(c: string) {
+export function isSpaceOrTabOrNewline(c: string) {
   return c === ' ' || c === '\t' || c === '\n';
 }
 

src/paint.ts

@@ -1,7 +1,7 @@
 import {BlockContainer, ReplacedBox, Inline, IfcInline} from './layout-flow.ts';
 import {Image} from './layout-image.ts';
 import {G_CL, G_AX, G_SZ} from './text-harfbuzz.ts';
-import {ShapedItem, Paragraph} from './layout-text.ts';
+import {ShapedItem, Paragraph, isSpaceOrTabOrNewline} from './layout-text.ts';
 import {Box, FormattingBox} from './layout-box.ts';
 import {binarySearchOf} from './util.ts';
 
@@ -26,12 +26,22 @@ export interface PaintBackend {
 }
 
 function getTextOffsetsForUncollapsedGlyphs(item: ShapedItem) {
+  const s = item.paragraph.string;
   const glyphs = item.glyphs;
   let glyphStart = 0;
   let glyphEnd = glyphs.length - G_SZ;
 
-  while (glyphStart < glyphs.length && glyphs[glyphStart + G_AX] === 0) glyphStart += G_SZ;
-  while (glyphEnd >= 0 && glyphs[glyphEnd + G_AX] === 0) glyphEnd -= G_SZ;
+  while (
+    glyphStart < glyphs.length &&
+    glyphs[glyphStart + G_AX] === 0 &&
+    isSpaceOrTabOrNewline(s[glyphs[glyphStart + G_CL]])
+  ) glyphStart += G_SZ;
+
+  while (
+    glyphEnd >= 0 &&
+    glyphs[glyphEnd + G_AX] === 0 &&
+    isSpaceOrTabOrNewline(s[glyphs[glyphEnd + G_CL]])
+  ) glyphEnd -= G_SZ;
 
   if (glyphStart in glyphs && glyphEnd in glyphs) {
     let textStart, textEnd;

test/paint.spec.js

@@ -675,6 +675,15 @@ describe('Painting', function () {
     ]);
   });
 
+  it('doesn\'t break clusters when trimming whitespace', function () {
+    registerFontAsset('NotoSansArabic/NotoSansArabic-Regular.ttf');
+    this.layout('<div style="font: 10px Noto Sans Arabic;">والمهارة</div>');
+    expect(this.paint().getCalls()).to.deep.equal([
+      {t: 'text', x: 0, y: 13.74, text: 'والمهارة', fillColor: '#000'}
+    ]);
+    unregisterFontAsset('NotoSansArabic/NotoSansArabic-Regular.ttf');
+  });
+
   // TODO: would go better in a general box.spec.js
   describe('Pixel snapping', function () {
     it('snaps the border box', function () {