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Improve the stem darkening vertical extents preservation hack

This commit is contained in:
Patrick Walton 2017-11-10 08:40:31 -08:00
parent a73fb9ab8d
commit 2f7205bd22
1 changed files with 16 additions and 5 deletions
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21
demo/client/src/text-renderer.ts
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@ -32,6 +32,8 @@ interface AntialiasingStrategyTable {
xcaa: typeof AdaptiveMonochromeXCAAStrategy;
}
const SQRT_1_2: number = 1.0 / Math.sqrt(2.0);
const MIN_SCALE: number = 0.0025;
const MAX_SCALE: number = 0.5;
@ -240,11 +242,20 @@ export abstract class TextRenderer extends Renderer {
const atlasGlyphs = this.renderContext.atlasGlyphs;
const pixelsPerUnit = this.displayPixelsPerUnit;
// FIXME(pcwalton): This is a hack that tries to align glyphs on their baselines after
// stem darkening. It's better than nothing, but we should really do better.
const stemDarkeningOffset = glmatrix.vec2.clone(this.stemDarkeningAmount);
// FIXME(pcwalton): This is a hack that tries to preserve the vertical extents of the glyph
// after stem darkening. It's better than nothing, but we should really do better.
//
// This hack seems to produce *better* results than what macOS does on sans-serif fonts;
// the ascenders and x-heights of the glyphs are pixel snapped, while they aren't on macOS.
// But we should really figure out what macOS does…
const ascender = this.renderContext.font.opentypeFont.ascender;
const stemDarkeningAmount = this.stemDarkeningAmount;
const stemDarkeningYScale = (ascender + stemDarkeningAmount[1]) / ascender;
const stemDarkeningOffset = glmatrix.vec2.clone(stemDarkeningAmount);
glmatrix.vec2.scale(stemDarkeningOffset, stemDarkeningOffset, pixelsPerUnit);
glmatrix.vec2.scale(stemDarkeningOffset, stemDarkeningOffset, 1.0 / Math.sqrt(2.0));
glmatrix.vec2.scale(stemDarkeningOffset, stemDarkeningOffset, SQRT_1_2);
glmatrix.vec2.mul(stemDarkeningOffset, stemDarkeningOffset, [1, stemDarkeningYScale]);
const transforms = new Float32Array((pathCount + 1) * 4);
@ -253,7 +264,7 @@ export abstract class TextRenderer extends Renderer {
const atlasOrigin = glyph.calculateSubpixelOrigin(pixelsPerUnit);
transforms[pathID * 4 + 0] = pixelsPerUnit;
transforms[pathID * 4 + 1] = pixelsPerUnit;
transforms[pathID * 4 + 1] = pixelsPerUnit * stemDarkeningYScale;
transforms[pathID * 4 + 2] = atlasOrigin[0] + stemDarkeningOffset[0];
transforms[pathID * 4 + 3] = atlasOrigin[1] + stemDarkeningOffset[1];
}