marfrit
a4e7d8ab90
panvk-bifrost campaigns (r1..r4 Vulkan compositor + r5.video1 Vulkan
video decode) shipped before this repo existed; the deliverable
patches live in marfrit-packages, but the reasoning chain, phase docs,
and source-state evidence lived only in local working trees on the
development host.
This retrofit imports:
- mesa-panvk-bifrost/ — r1..r4 era phase docs (iter1..iter18)
(libmali stub blobs at iter18/blob/ excluded
— 109MB of RE artifacts replaced with a README
pointer)
- mesa-panvk-bifrost-video/ — sibling campaign phase docs + probe
- evidence/ — frozen .tgz source snapshots at each milestone
(basis for the 0005 patch diff generation)
Future iterations should branch off here from day one, so each iter is
a commit rather than a snapshot. See [[feedback-session-local-process-pins]]
for the process drift this retrofit closes.
Total: 1.9 MB across 124 files.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
64 lines
3.3 KiB
Markdown
64 lines
3.3 KiB
Markdown
# Phase 0 — substrate for iter6
|
||
|
||
Opened **2026-05-19** after [iter5 close GREEN](phase8_iteration5_close.md).
|
||
|
||
## Locked research question — iter6
|
||
|
||
> **Render a depth-tested scene into a 128×128 RGBA8 color attachment + 128×128 D32_SFLOAT depth attachment via dynamic rendering:**
|
||
>
|
||
> - **Triangle A (red):** large, NDC (-0.8,-0.8), (0.8,-0.8), (0.0,0.8), all with z=0.7
|
||
> - **Triangle B (green):** small, NDC (-0.4,-0.4), (0.4,-0.4), (0.0,0.4), all with z=0.3 — fully geometrically inside Triangle A
|
||
> - Draw A first, then B. Depth test enabled (`VK_COMPARE_OP_LESS`).
|
||
> - Triangle B's lower z should make it appear in front of A wherever they overlap.
|
||
>
|
||
> **Verify specific pixels:**
|
||
> 1. `(0, 0)` — clear (outside both, top-left corner)
|
||
> 2. `(127, 127)` — clear (outside both, bottom-right corner)
|
||
> 3. `(64, 64)` — inside both, GREEN (B in front)
|
||
> 4. `(64, 30)` — inside A only (above B's reach in pixel-y), RED
|
||
> 5. `(64, 100)` — inside A only (below B's reach), RED
|
||
|
||
## Why this shape
|
||
|
||
iter5 closed all single-draw, no-depth, descriptor-binding paths. iter6 adds:
|
||
|
||
- **Depth/stencil attachment** (D32_SFLOAT) — new image format, new aspect, new usage flag (DEPTH_STENCIL_ATTACHMENT)
|
||
- **Depth test + depth write** in pipeline state (`VkPipelineDepthStencilStateCreateInfo`)
|
||
- **Multi-draw within one render pass** — two `vkCmdDraw` calls between begin/end
|
||
- **z-coordinate handling** in the vertex shader (gl_Position.z affects depth)
|
||
- **128×128 image** instead of 64×64 (more tiles — 8×8 grid of 16×16 = 64 tiles)
|
||
- **Depth attachment format** in `VkPipelineRenderingCreateInfoKHR.depthAttachmentFormat`
|
||
- **Depth attachment** in `VkRenderingInfoKHR.pDepthAttachment`
|
||
|
||
## Hypothesis space
|
||
|
||
1. **D32_SFLOAT depth format on Bifrost.** Bifrost packs depth into tiles; the layout differs from color. First time we use a non-color attachment.
|
||
2. **Depth-stencil image creation + layout (`DEPTH_STENCIL_ATTACHMENT_OPTIMAL`).** New layout never used.
|
||
3. **Depth test plumbing.** PanVk-Bifrost's path from `VkPipelineDepthStencilStateCreateInfo` → tile descriptor depth-state fields.
|
||
4. **Depth write back to depth attachment.** Mali stores depth in tile memory then flushes; per-tile flush + cache invalidation.
|
||
5. **Multi-draw within one render pass.** Bifrost's binner may have bugs handling N>1 jobs per render pass — particularly around per-draw state changes.
|
||
6. **z-coordinate from vertex shader.** Vertex output position.z passes through to rasterizer.
|
||
7. **Tile binning at 128×128** (64 tiles vs. iter3's 16). More potential for binner state bugs.
|
||
|
||
## In-scope (LOCKED 2026-05-19 for iter6)
|
||
|
||
- 128×128 RGBA8 color + 128×128 D32_SFLOAT depth attachment.
|
||
- 6 vertices (2 triangles) in one vertex buffer, vec3 pos + vec3 color.
|
||
- Depth test enabled, depth write enabled, compare LESS.
|
||
- Two `vkCmdDraw(3, 1, *, 0)` calls within one render pass.
|
||
- 5-point pixel-level verification.
|
||
|
||
## Out-of-scope (LOCKED 2026-05-19 for iter6)
|
||
|
||
- Stencil (D32_SFLOAT has no stencil aspect anyway).
|
||
- D24_UNORM_S8_UINT or other depth formats (iter would explore if iter6 fails).
|
||
- Depth clear via load-op only (no separate clear-image).
|
||
- Front-face culling, polygon-mode lines.
|
||
- Indexed draws.
|
||
- More than 2 triangles.
|
||
- WSI / surface — still off-screen attachment + buffer readback.
|
||
|
||
## Reference
|
||
|
||
- Prior closes: [iter1](phase8_iteration1_close.md) — [iter5](phase8_iteration5_close.md).
|