[monotykamary]

Objective

• Provide GPUIX with the GPUI primitives needed to update a stable polychrome image without rebuilding retained views or reallocating a same-sized atlas tile.
• This is the prerequisite for remorses/gpuix#40 and the fixed-cell terminal proposed in remorses/gpuix#42.

Solution

• Add RenderImage::from_bgra for tightly packed, single-frame pixel buffers.
• Add PlatformAtlas::update, with in-place uploads for Metal, WGPU, and DirectX and the existing remove/reinsert behavior as the default fallback.
• Add an explicit per-sprite nearest-neighbor flag while preserving the existing polychrome sprite layout. Ordinary images and color glyphs remain linearly sampled; monochrome and subpixel glyph paths are unchanged.
• Add Window::update_image, which reports whether every atlas tile retained its identity, and Window::present_cached_frame for safely presenting that updated stable scene.

The separate monochrome glyph sampling discussion in zed-industries/zed#57777 and zed-industries/zed#57781 is intentionally out of scope.

Testing

• cargo test -p gpui -p gpui_apple --lib --features gpui_apple/runtime_shaders — 269 GPUI tests and 4 Metal atlas tests passed.
• cargo test -p gpui_wgpu --lib — 31 tests passed, including same-size reuse, resize fallback, BGRA swizzling, WGSL validation, WebGL transport, and sprite stride coverage.
• ./script/clippy -p gpui_apple, ./script/clippy -p gpui_wgpu, and ./script/clippy -p gpui_windows passed.
• cargo clippy -p gpui --release --lib --all-features -- --deny warnings passed. The repository wrapper's all-target GPUI run is currently blocked by a pre-existing redundant_clone lint in crates/gpui/src/interactive.rs:881.
• Instantiated MetalHeadlessRenderer with runtime shaders to compile the complete changed Metal shader successfully.
• Ran the downstream GPUix native suite against this worktree with runtime Metal shaders: 227 tests passed.
• Rust formatting and git diff --check passed.

Tested on macOS Apple Silicon. Metal and WGPU executed locally. The DirectX implementation was linted but requires Windows CI or hardware for runtime validation.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

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Release Notes:

• N/A