Core: Add support for colorized SDF fill patterns

[deniial00]

Description

Implements Support colorized SDF fill patterns.

When a fill-pattern references an SDF image, the renderer now:

• Uses fill-color as the pattern foreground color.
• Supports constant and data-driven colors.
• Applies fill-opacity.
• Supports the antialiased fill-outline path.
• Keeps existing RGBA pattern rendering unchanged.

Implementation

• Allows fill-color together with fill-pattern in the bundled style specification.
• Preserves SDF metadata through ImagePosition and the pattern atlas.
• Tracks whether each fill layer uses SDF patterns.
• Passes the SDF state to the fill-pattern shaders.
• Adds SDF alpha evaluation and antialiasing for OpenGL, Metal, Vulkan, and WebGPU.
• Triggers relayout when an image changes between RGBA and SDF.
• Emits a warning when SDF and non-SDF patterns are mixed within one layer.
• Documents the SDF foreground-color behavior in the style specification and generated Android and Darwin APIs.

No public API changes are required.

Testing

• Added unit tests for SDF metadata preservation.
• Added backend-independent tests for per-layer pattern-type tracking and mixed-pattern warnings across buckets.
• Added a render test covering:
  • Constant SDF color
  • Data-driven SDF colors
  • fill-opacity
  • Antialiased outlines
  • Unchanged RGBA pattern rendering
• Locally verified the Metal build, relevant unit tests, and the SDF fill-pattern render test.
• Locally verified the WebGPU/wgpu build and focused render test.
• Compiled the affected OpenGL core and test objects. The full backend and platform matrix, including Vulkan, is left to CI.

Related work

• MapLibre Style Specification #1683
• MapLibre GL JS #8239

AI assistance

OpenAI Codex was used for implementation review, warning deduplication, regression testing, and generated documentation checks. The contributor has reviewed and verified the submitted changes before marking this draft ready for review.

Fixes #4526

[louwers]

Thanks!

Could you make sure all the render tests from the MapLibre GL JS PR are ported?

Also, let's wait with merging this until the MapLibre GL JS PR is merged.

I'm kicking off a workflow run, please ping me if you need another one.

[github-actions]

Bloaty Results (iOS) 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +12.4Ki  +0.1% +16.0Ki    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results-ios/pr-4551-compared-to-main.txt

[deniial00]

@louwers maplibre/maplibre-gl-js#8239 has now been merged, and all four render tests from it are ported here. The fixes for the Linux, WebGPU, and Vulkan failures are also pushed. Could you kick off another workflow run when you have a chance? Thanks!

[github-actions]

Bloaty Results 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1%  +249Ki  +0.2% +59.8Ki    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-4551-compared-to-main.txt

Compared to d387090 (legacy)

    FILE SIZE        VM SIZE    
 --------------  -------------- 
   +56% +64.5Mi  +477% +28.5Mi    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-4551-compared-to-legacy.txt

[github-actions]

Benchmark Results ⚡

Benchmark                                                          Time             CPU      Time Old      Time New       CPU Old       CPU New
-----------------------------------------------------------------------------------------------------------------------------------------------
OVERALL_GEOMEAN                                                 -0.0024         -0.0017             0             0             0             0

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/benchmark-results/pr-4551-compared-to-main.txt

[louwers]

Is there any way to avoid these static variables?

[deniial00]

Addressed in d5a7656. The warning suppression set now belongs to each FillBucket, so there are no function-local statics or mutex. The test verifies that repeated mismatches warn once within a bucket and that separate buckets do not share warning state.