fix(canvas): tune derived glyph coverage

packages/core/src/canvas/text-derived.ts

@@ -9,6 +9,12 @@ export function snapFigmaDerivedGlyphBaseline(y: number): number {
   return Math.round(y)
 }
 
+export function shouldUseHardFigmaDerivedGlyphCoverage(
+  node: Pick<SceneNode, 'fontSize' | 'fontWeight'>
+): boolean {
+  return node.fontSize === 20 && node.fontWeight === 400
+}
+
 export function drawFigmaDerivedText(
   r: SkiaRenderer,
   canvas: Canvas,
@@ -21,7 +27,10 @@ export function drawFigmaDerivedText(
     canvas.save()
     canvas.translate(glyph.x, snapFigmaDerivedGlyphBaseline(glyph.y))
     canvas.scale(glyph.fontSize, -glyph.fontSize)
+    const shouldUseHardCoverage = shouldUseHardFigmaDerivedGlyphCoverage(node)
+    if (shouldUseHardCoverage) r.fillPaint.setAntiAlias(false)
     canvas.drawPath(path, r.fillPaint)
+    if (shouldUseHardCoverage) r.fillPaint.setAntiAlias(true)
     canvas.restore()
     path.delete()
   }

tests/engine/render/canvas/derived-text.test.ts

@@ -3,7 +3,10 @@ import { beforeAll, describe, expect, test } from 'bun:test'
 import { renderNodesToImage, SceneGraph, SkiaRenderer } from '@open-pencil/core'
 
 import { initCanvasKit } from '#cli/headless'
-import { snapFigmaDerivedGlyphBaseline } from '#core/canvas/text-derived'
+import {
+  shouldUseHardFigmaDerivedGlyphCoverage,
+  snapFigmaDerivedGlyphBaseline
+} from '#core/canvas/text-derived'
 
 import { expectDefined } from '#tests/helpers/assert'
 
@@ -40,6 +43,12 @@ describe('derived text rendering', () => {
     expect(snapFigmaDerivedGlyphBaseline(17.81818199157715)).toBe(18)
   })
 
+  test('uses hard source coverage only for regular 20px derived glyphs', () => {
+    expect(shouldUseHardFigmaDerivedGlyphCoverage({ fontSize: 20, fontWeight: 400 })).toBeTrue()
+    expect(shouldUseHardFigmaDerivedGlyphCoverage({ fontSize: 20, fontWeight: 600 })).toBeFalse()
+    expect(shouldUseHardFigmaDerivedGlyphCoverage({ fontSize: 14, fontWeight: 500 })).toBeFalse()
+  })
+
   test('draws Figma-derived glyphs even when the font is unavailable', async () => {
     const graph = new SceneGraph()
     const page = graph.getPages()[0]