Opt-in batch_group regrouping cuts texture binds; prepare_draw_batches and draw_list tests lock the contract so end_frame cannot silently drop regroup.
- `draw_sprite` now builds verts on the CPU and appends to a per-frame draw list instead of uploading mid-render-pass.
- `begin_frame` only acquires the command buffer / swapchain; `end_frame` does one copy pass on that same buffer, then the render pass, then submit.
- Removes the second command buffer + `WaitForGPUFences` that stalled the CPU once per sprite every frame.
- Vertex/transfer buffers sized for `MAX_SPRITES` (128). Example API unchanged: `begin_frame` → `draw_sprite` → `end_frame`.
- Pulled pure logic out of GPU-facing code so it can be tested without a window: parse_char_def (JSON → Char_Def) and choose_shader_runtime_from_formats (MSL → DXIL → SPIR-V preference)
- Added eight Odin @(test) cases in engine/ covering happy/bad JSON parse, frame-rect hit/miss/OOB, clip-space conversion corners, shader filename mapping, and backend selection
- Added make test to run odin test engine
Adds a runtime GPU shader-backend selection layer so the engine is no longer hardcoded to #load SPIR-V only.
- Introduce Shader_Runtime / choose_shader_runtime (engine/shader_backend.odin)
- Create the GPU device with {.SPIRV, .DXIL, .MSL}, then pick a supported format + shaders/<backend>/ directory
- Load shader blobs from disk and build the sprite pipeline with the chosen format/entrypoint
- Add shader build scripts + Makefile targets (shaders-vulkan / d3d12 / metal / all)
Migrates the toad example from SDL’s 2D Renderer API to SDL_GPU, keeping the same Character_Data / Sprite engine API and baked asset pipeline.
- Replaces CreateWindowAndRenderer / RenderTexture with GPU device + swapchain framing (begin_frame / end_frame)
- Adds sprite vertex/fragment GLSL shaders and compiled SPIR-V (shaders/sprite.*.glsl / .spv)
- Uploads atlas PNGs as GPUTexture via transfer buffer + copy pass (with fence sync)
- Draws sprites as UV quads (DrawGPUPrimitives) using atlas frame rects from char.json
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