Adds IconComposer (AcDream.App.UI) which mirrors retail IconData::RenderIcons
(decomp 407524): decodes each RenderSurface layer directly via SurfaceDecoder,
composites them bottom-to-top with Porter-Duff alpha-over, and uploads the
result to a GL texture via TextureCache. Composited handles are keyed by the
(iconId, underlayId, overlayId) tuple so each unique combo is uploaded once.
Adds a public TextureCache.UploadRgba8(byte[], int, int, bool) wrapper — a
thin shell around the existing private overload — so IconComposer can upload
its CPU-side composite without duplicating any GL state logic.
Pure Compose() path is covered by 2 unit tests (opaque top wins; transparent
top preserves bottom). Dat-decode + GL-upload exercised by the visual gate.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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