Two faithful, deterministic GPU-backend changes that make the texture path
correct for whatever textured draw the splash eventually dispatches. Both are
currently inert on Sylpheed (the textured logo draw is still gated downstream
— see below), but neither shifts the stable-digest golden, so they land safely.
1. Un-stub RectangleList primitive expansion (primitive.rs). The splash submits
2819 RectangleList draws at 200M, all of which were REJECTED by the P3 stub
(`gpu.primitive.rejected{rectangle_list}`) → only ~592 flat point/quad draws
rasterized. Mirror canary's intent (primitive_processor.cc:389-456
kRectangleListAsTriangleStrip) within our CPU index-rewrite idiom: emit each
rect's 3 real vertices as one TriangleList triangle (v0,v1,v2), rejected=false,
faithful host_vertex_count. The full quad (synthesized 4th corner v3=v0+v2-v1)
needs real vertex fetch in vs_main — left as a documented TODO. Rejection
warnings drop 2819→0.
2. Draw-time texture decode keyed off the active PS's real tfetch slots
(gpu_system.rs + exports.rs vd_swap). Previously vd_swap decoded a hardcoded
fetch-constant slot 0 at swap time. Now the DRAW handler parses the bound
pixel shader (ucode::parse_shader), collects its tfetch fetch_const slots via
new shader_metrics::tfetch_slots, reads each 6-dword fetch constant, and
decode+caches it into GpuSystem::last_draw_textures. vd_swap publishes the
first of these (UI binds one texture today), falling back to the legacy slot-0
probe on flat-only frames. New span_max_version helper walks page_version over
the trait (draw-time &dyn MemoryAccess lacks the heap's inherent
max_page_version). Pure function of guest writes — deterministic.
Status: texture_decodes stays 0 on Sylpheed because all 6 live shaders are flat
(no tfetch); canary's textured logo shaders E59B2B3D/F7B1457 are not yet
dispatched by ours (a downstream title-state gate, the next frontier). The full
P5 decode→publish→upload→sample path is already wired; this makes the decode
side key off the real shader instead of a guess.
Validation: stable-digest golden sylpheed_n50m unchanged (draws=718 swaps=147
tex=0), regenerated twice byte-identical; 200M run shows 0 RectangleList
rejections. cargo test --workspace green (677, +2: rectangle_list_expansion,
tfetch_slots_extracts_texture_fetch_constants). No temp hooks. Branch only;
not pushed/merged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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