Improve the stem darkening vertical extents preservation hack
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@ -32,6 +32,8 @@ interface AntialiasingStrategyTable {
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xcaa: typeof AdaptiveMonochromeXCAAStrategy;
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}
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const SQRT_1_2: number = 1.0 / Math.sqrt(2.0);
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const MIN_SCALE: number = 0.0025;
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const MAX_SCALE: number = 0.5;
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@ -240,11 +242,20 @@ export abstract class TextRenderer extends Renderer {
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const atlasGlyphs = this.renderContext.atlasGlyphs;
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const pixelsPerUnit = this.displayPixelsPerUnit;
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// FIXME(pcwalton): This is a hack that tries to align glyphs on their baselines after
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// stem darkening. It's better than nothing, but we should really do better.
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const stemDarkeningOffset = glmatrix.vec2.clone(this.stemDarkeningAmount);
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// FIXME(pcwalton): This is a hack that tries to preserve the vertical extents of the glyph
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// after stem darkening. It's better than nothing, but we should really do better.
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//
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// This hack seems to produce *better* results than what macOS does on sans-serif fonts;
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// the ascenders and x-heights of the glyphs are pixel snapped, while they aren't on macOS.
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// But we should really figure out what macOS does…
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const ascender = this.renderContext.font.opentypeFont.ascender;
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const stemDarkeningAmount = this.stemDarkeningAmount;
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const stemDarkeningYScale = (ascender + stemDarkeningAmount[1]) / ascender;
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const stemDarkeningOffset = glmatrix.vec2.clone(stemDarkeningAmount);
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glmatrix.vec2.scale(stemDarkeningOffset, stemDarkeningOffset, pixelsPerUnit);
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glmatrix.vec2.scale(stemDarkeningOffset, stemDarkeningOffset, 1.0 / Math.sqrt(2.0));
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glmatrix.vec2.scale(stemDarkeningOffset, stemDarkeningOffset, SQRT_1_2);
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glmatrix.vec2.mul(stemDarkeningOffset, stemDarkeningOffset, [1, stemDarkeningYScale]);
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const transforms = new Float32Array((pathCount + 1) * 4);
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@ -253,7 +264,7 @@ export abstract class TextRenderer extends Renderer {
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const atlasOrigin = glyph.calculateSubpixelOrigin(pixelsPerUnit);
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transforms[pathID * 4 + 0] = pixelsPerUnit;
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transforms[pathID * 4 + 1] = pixelsPerUnit;
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transforms[pathID * 4 + 1] = pixelsPerUnit * stemDarkeningYScale;
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transforms[pathID * 4 + 2] = atlasOrigin[0] + stemDarkeningOffset[0];
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transforms[pathID * 4 + 3] = atlasOrigin[1] + stemDarkeningOffset[1];
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}
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