Add color font palette support to C API by mattleibow · Pull Request #197 · mono/skia

mattleibow · 2026-04-25T17:02:21Z

Summary

Extends the variable font C API (merged in #185) with color palette support, enabling SkiaSharp to clone typefaces with specific palette selections and per-color overrides for COLRv1/COLR fonts.

Companion PR: mono/SkiaSharp#3742

Changes

New struct

sk_fontarguments_palette_override_t — maps to SkFontArguments::Palette::Override with index (uint16_t) and color (sk_color_t) fields

Extended function

sk_typeface_clone_with_arguments — extended from 4 to 7 parameters:
- paletteIndex — select a built-in palette by index
- paletteOverrides — pointer to array of color overrides
- paletteOverrideCount — number of overrides

Type mapping (sk_types_priv.h)

DEF_MAP(SkFontArguments::Palette::Override, sk_fontarguments_palette_override_t, PaletteOverride) — layout-compatible, uses reinterpret_cast
AsSkFontArguments helper updated to call setPalette() with the new parameters

ABI verification (sk_structs.cpp)

static_assert for sk_fontarguments_palette_override_t size matching SkFontArguments::Palette::Override

Files changed

File	Change
`include/c/sk_typeface.h`	New struct + extended function signature
`src/c/sk_typeface.cpp`	Updated clone implementation
`src/c/sk_types_priv.h`	DEF_MAP + updated AsSkFontArguments helper
`src/c/sk_structs.cpp`	static_assert for palette override

Expose SkTypeface variable font functionality through the C API: - sk_typeface_get_variation_design_position: query current axis coordinates - sk_typeface_get_variation_design_parameters: query axis metadata (tag, min, default, max, hidden) - sk_typeface_clone_with_arguments: create typeface clone with specific variation coordinates Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Replace reinterpret_cast between C and C++ structs with field-by-field copy. The structs have identical layout so the cast worked in practice, but accessing memory through an unrelated type is undefined behavior per the C++ standard. Compilers optimize the copy loop to the same code. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Add sk_fourbytetag_t typedef (uint32_t) matching SkFourByteTag - Use sk_fourbytetag_t in variation axis/coordinate C structs - Add AsVariationPositionCoordinate/ToVariationPositionCoordinate for layout-compatible Coordinate struct (verified by static_assert) - Add ToVariationAxis for Axis conversion (handles isHidden() getter) - Add AsSkFontArguments helper for clone_with_arguments - Simplify sk_typeface.cpp: remove manual copy loops, use reinterpret_cast for coordinates, use helpers for parameters and font arguments Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Replace manual reinterpret_cast functions with DEF_MAP macro for VariationPosition::Coordinate (generates As*/To* automatically) - Move static_assert to sk_structs.cpp following existing pattern - Use AsVariationPositionCoordinate() in sk_typeface.cpp instead of inline reinterpret_cast Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Add sk_fontarguments_palette_override_t struct - Extend sk_typeface_clone_with_arguments with palette parameters - Add DEF_MAP for Palette::Override (layout-compatible) - Add static_assert for Palette::Override size check - Update AsSkFontArguments to pass palette through Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- Replace manual reinterpret_cast functions with DEF_MAP macro for VariationPosition::Coordinate (generates As*/To* automatically) - Move static_assert to sk_structs.cpp following existing pattern - Use AsVariationPositionCoordinate() in sk_typeface.cpp instead of inline reinterpret_cast Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

The generator reads harfbuzz headers to produce HarfBuzzApi.generated.cs. It needs the 2.8.2 headers (63e15eac) not the build-time version. The build-time harfbuzz version is controlled separately by the native build. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

This reverts commit 4ae600d.

…-enhancements # Conflicts: # include/c/sk_typeface.h # src/c/sk_structs.cpp # src/c/sk_typeface.cpp # src/c/sk_types_priv.h

Copilot

Pull request overview

This PR extends the Skia C typeface/variable-font API to support OpenType color palettes by introducing a palette override struct and plumbing palette selection/overrides through the typeface cloning API.

Changes:

Added sk_fontarguments_palette_override_t to represent CPAL entry overrides (index + color).
Extended sk_typeface_clone_with_arguments to accept palette index and override list/count.
Added C↔C++ struct mapping and ABI size static-asserts for the new palette override type.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
`src/c/sk_types_priv.h`	Adds `DEF_MAP` for `SkFontArguments::Palette::Override` and extends `AsSkFontArguments` to set palette arguments.
`src/c/sk_typeface.cpp`	Updates `sk_typeface_clone_with_arguments` implementation to pass palette args into `SkTypeface::makeClone`.
`src/c/sk_structs.cpp`	Adds `static_assert` to ensure C/C++ palette override struct sizes match.
`include/c/sk_typeface.h`	Introduces `sk_fontarguments_palette_override_t` and extends the public C API function signature for cloning with arguments.

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…3742) Add color font palette support and improve variable font robustness (#3742) Requires: mono/skia#197 Extends the variable font support merged in #3703 with color font palette APIs, Span method robustness fixes, and a pre-existing bug fix. ~~ Color font palette support ~~ SkiaSharp: * SKTypeface.Clone(int paletteIndex) — clone with a built-in palette * SKTypeface.Clone(SKFontArguments) — clone with palette index, per-color overrides, variation position, and collection index * SKFontArguments ref struct gains PaletteIndex and PaletteOverrides * SKFontPaletteOverride struct for individual color entry overrides HarfBuzzSharp: * Face.HasPalettes, PaletteCount — query color font support * Face.GetPaletteColors (array + Span) — retrieve palette entries * Face.GetPaletteFlags, GetPaletteNameId, GetPaletteColorNameId * Face.HasColorLayers, HasColorPng, HasColorSvg C API (mono/skia#197): * sk_fontarguments_palette_override_t struct * sk_typeface_clone_with_arguments extended with palette parameters * DEF_MAP + static_assert for Palette::Override ~~ Span method robustness ~~ Skia's getVariationDesignParameters/Position use all-or-nothing semantics: if the buffer is undersized, they return the total count but write nothing. The C# Span methods now detect this and retry with a pooled buffer (ArrayPool), copying what fits. Empty spans return 0 immediately without native calls or allocations. Font.GetVariationCoordsNormalized(Span) fixed to return the written count instead of the total length when the buffer is undersized. ~~ Bug fix ~~ SKTypeface.ContainsGlyphs(ReadOnlySpan<byte>, SKTextEncoding) had a pre-existing infinite recursion (called itself instead of GetFont().ContainsGlyphs) causing StackOverflowException. ~~ Test coverage ~~ Every Span API tested across empty, undersized, exact, and oversized buffers with exact assertions. Palette APIs tested for colors, flags, name IDs, different palettes, and negative index validation. Added InterVariable.ttf (multi-axis) and test_glyphs-COLRv1.ttf (3 palettes) as test fonts. Gallery sample demonstrates Nabla (COLRv1, 7 palettes, variable axes) with palette picker and weight/optical size sliders. Co-authored-by: Ramez Gerges <ramezragaa@proton.me> Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

ramezgerges and others added 7 commits April 19, 2026 18:30

Merge remote-tracking branch 'origin/skiasharp' into HEAD

2aa5c11

mattleibow mentioned this pull request Apr 25, 2026

Add color font palette support and improve variable font robustness mono/SkiaSharp#3742

Merged

mattleibow and others added 6 commits April 25, 2026 23:00

Merge remote-tracking branch 'origin/skiasharp' into dev/variable-fonts

d53076c

Merge remote-tracking branch 'origin/skiasharp' into dev/variable-fonts

0afa08b

Merge dev/variable-fonts into dev/font-enhancements

73780c8

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Revert "Use harfbuzz 2.8.2 SHA for binding generation"

bfad665

This reverts commit 4ae600d.

Merge commit 'b6a88e589ff5ba70b7ded741ce35893565039b34' into dev/font…

a162e5c

…-enhancements # Conflicts: # include/c/sk_typeface.h # src/c/sk_structs.cpp # src/c/sk_typeface.cpp # src/c/sk_types_priv.h

mattleibow requested a review from Copilot April 26, 2026 13:22

Copilot started reviewing on behalf of mattleibow April 26, 2026 13:22 View session

Copilot AI reviewed Apr 26, 2026

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Comment thread include/c/sk_typeface.h

mattleibow marked this pull request as ready for review April 26, 2026 16:21

mattleibow changed the title ~~Add variable font and color palette C API~~ Add color font palette support to C API Apr 26, 2026

mattleibow merged commit b9b89f2 into skiasharp Apr 26, 2026
5 checks passed

mattleibow deleted the dev/font-enhancements branch April 26, 2026 16:31

mattleibow mentioned this pull request May 8, 2026

[FEATURE] Expose additional API for variable font support mono/SkiaSharp#2397

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Add color font palette support to C API#197

Add color font palette support to C API#197
mattleibow merged 13 commits into
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dev/font-enhancements

mattleibow commented Apr 25, 2026 •

edited

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mattleibow commented Apr 25, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

Changes

New struct

Extended function

Type mapping (sk_types_priv.h)

ABI verification (sk_structs.cpp)

Files changed

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mattleibow commented Apr 25, 2026 •

edited

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