- Add shared UBO layout across vertex + fragment stages so vertex
uniforms like ove_mvpmat compile and bind correctly.
- Rewrite uniform extraction/injection to avoid corrupting the UBO
block and to keep explicit sampler bindings stable.
- Make the UBO and sampler descriptor bindings visible to both vertex
and fragment stages.
- Add layout locations for vertex varyings (ove_texcoord) and fragment
inputs so SPIR-V generation succeeds.
- Extend TransitionImageLayout() to cover all layout pairs used by
upload/download/clear/blit.
- Add subpass dependencies to the cached render pass and leave
destinations in SHADER_READ_ONLY_OPTIMAL after Blit().
- Move descriptor allocation before command recording and abort cleanly
if allocation fails; switch Blit() to the persistent linear sampler.
- Add a gtest that creates a Vulkan backend, uploads a red U8 RGBA
texture, blits through the default pass-through shader, and verifies
the downloaded pixel is red. This test passes on the current system.
ctest passes 4/4; DynamicRenderBackend.* passes 3/1 (Vulkan fallback
skipped because Vulkan is available).