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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
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18
src/display/text_layer.js
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@ -81,7 +81,7 @@ class TextLayer {
static #ascentCache = new Map();
static #canvasCtx = null;
static #canvasContexts = new Map();
static #pendingTextLayers = new Set();
@ -423,13 +423,15 @@ class TextLayer {
return;
}
this.#ascentCache.clear();
this.#canvasCtx?.canvas.remove();
this.#canvasCtx = null;
for (const { canvas } of this.#canvasContexts.values()) {
canvas.remove();
}
this.#canvasContexts.clear();
}
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
// fonts with it and they depends on the locale.
// In Firefox, the <html> element get a lang attribute that depends on
@ -442,10 +444,12 @@ class TextLayer {
// OffscreenCanvas.
const canvas = document.createElement("canvas");
canvas.className = "hiddenCanvasElement";
canvas.lang = lang;
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) {