26 lines
1.0 KiB
TypeScript
26 lines
1.0 KiB
TypeScript
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import type { Font, Measure } from "./types.js";
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export const fontString = (font: Font) =>
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`${font.italic ? "italic " : ""}${font.weight === "bold" ? "bold " : ""}${font.size}px ${font.family}`;
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// A bounded per-surface cache replaces the original global memoizee cache.
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// Font loading creates a new measure/layout so fallback metrics cannot persist.
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export function canvasMeasure(context: CanvasRenderingContext2D, maximum = 12000): Measure {
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const cache = new Map<string, ReturnType<Measure>>();
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return (text, font) => {
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const key = `${fontString(font)}/${text}`;
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const cached = cache.get(key);
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if (cached) return cached;
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context.font = fontString(font);
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const metrics = context.measureText(text);
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const value = {
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width: Math.max(0, metrics.width),
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ascent: Math.max(metrics.actualBoundingBoxAscent || 0, font.size * 0.85),
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descent: Math.max(metrics.actualBoundingBoxDescent || 0, font.size * 0.22),
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};
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if (cache.size >= maximum) cache.clear();
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cache.set(key, value);
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return value;
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};
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}
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