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Add lang attribute to canvas element

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Fixes issue #16843.
In certain cases, the text layer was misaligned
due to a difference between the `lang` attribute
of the viewer and the canvas. This commit addresses
the problem by adding the `lang` attribute to the canvas.

The issue was caused because PDF.js uses serif/sans-serif
fonts to generate the text layer and relies on system fonts.
The difference in the `lang` attribute led to different fonts
being picked, causing the misalignment.
This commit is contained in:
Aditi 2024-05-17 14:35:21 +05:30
parent 9ee7c07b83
commit 9edca0a5ed
3 changed files with 21 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

18
src/display/text_layer.js
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@ -81,7 +81,7 @@ class TextLayer {
static #ascentCache = new Map(); static #ascentCache = new Map();
static #canvasCtx = null; static #canvasContexts = new Map();
static #pendingTextLayers = new Set(); static #pendingTextLayers = new Set();
@ -423,13 +423,15 @@ class TextLayer {
return; return;
} }
this.#ascentCache.clear(); this.#ascentCache.clear();
for (const { canvas } of this.#canvasContexts.values()) {
this.#canvasCtx?.canvas.remove(); canvas.remove();
this.#canvasCtx = null; }
this.#canvasContexts.clear();
} }
static #getCtx(lang = null) { static #getCtx(lang = null) {
if (!this.#canvasCtx) { let canvasContext = this.#canvasContexts.get((lang ||= ""));
if (!canvasContext) {
// We don't use an OffscreenCanvas here because we use serif/sans serif // We don't use an OffscreenCanvas here because we use serif/sans serif
// fonts with it and they depends on the locale. // fonts with it and they depends on the locale.
// In Firefox, the <html> element get a lang attribute that depends on // In Firefox, the <html> element get a lang attribute that depends on
@ -442,10 +444,12 @@ class TextLayer {
// OffscreenCanvas. // OffscreenCanvas.
const canvas = document.createElement("canvas"); const canvas = document.createElement("canvas");
canvas.className = "hiddenCanvasElement"; canvas.className = "hiddenCanvasElement";
canvas.lang = lang;
document.body.append(canvas); document.body.append(canvas);
this.#canvasCtx = canvas.getContext("2d", { alpha: false }); canvasContext = canvas.getContext("2d", { alpha: false });
this.#canvasContexts.set(lang, canvasContext);
} }
return this.#canvasCtx; return canvasContext;
} }
static #getAscent(fontFamily, lang) { static #getAscent(fontFamily, lang) {

1
test/pdfs/issue16843.pdf.link Normal file
View file

@ -0,0 +1 @@
https://github.com/mozilla/pdf.js/files/12366234/16_2020-044.pdf

9
test/test_manifest.json
View file

@ -2202,6 +2202,15 @@
"lastPage": 1, "lastPage": 1,
"type": "eq" "type": "eq"
}, },
{
"id": "issue16843-text",
"file": "pdfs/issue16843.pdf",
"md5": "2845b2f7f02690c388c24c488297028a",
"rounds": 1,
"link": true,
"lastPage": 1,
"type": "text"
},
{ {
"id": "issue5509", "id": "issue5509",
"file": "pdfs/issue5509.pdf", "file": "pdfs/issue5509.pdf",