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>
60 lines
3.2 KiB
Markdown
60 lines
3.2 KiB
Markdown
# Phase 0 — substrate for iter5
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Opened **2026-05-19** after [iter4 close GREEN](phase8_iteration4_close.md).
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## Locked research question — iter5
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> **Render a non-fullscreen triangle into a 64×64 R8G8B8A8_UNORM attachment via a vertex buffer + UBO. Vertex buffer: 3 vertices, each (pos vec2 + color vec3) = 20 bytes (with 8-byte align padding → 32-byte stride). UBO: single mat4 transform (scaling 0.8 in x/y, identity otherwise). Triangle in scaled-NDC: v0(-0.5,-0.5) red, v1(0.5,-0.5) green, v2(0,0.5) blue. Fragment shader outputs interpolated color (mixed RGB at centroid).**
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>
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> **Verify:**
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> 1. **Centroid pixel** (32, 28) has all of R, G, B > 0x10 (interpolated, non-black).
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> 2. **Top-left pixel** (0, 0) is exactly 0x00000000 (clear, outside triangle).
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> 3. **Top-right pixel** (63, 0) is exactly 0x00000000 (clear, outside triangle).
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> 4. **Covered pixel count** (non-clear pixels) ∈ [800, 1600] (triangle area ≈ 1310 pixels).
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>
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> If GREEN: iter6 stress-tests with a multi-draw scene or a Zink-on-PanVk smoke. If RED: characterize vertex input / UBO descriptor / NIR varying interpolation.
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## Why this shape
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iter4 closed the descriptor model for fragment-stage texture binding. iter5 adds **vertex-stage descriptor binding** + **vertex input** (the vertex-side counterpart). What's new:
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- Vertex buffer (`VK_BUFFER_USAGE_VERTEX_BUFFER_BIT`) + `vkCmdBindVertexBuffers`
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- `VkPipelineVertexInputStateCreateInfo` with non-empty bindings + attributes (pos location 0, color location 1)
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- UBO (`VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER`) bound to vertex stage
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- Vertex shader reads attribute layouts + UBO via descriptor
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- Interpolated varying (color) from vertex → fragment
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## Hypothesis space
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1. **Vertex input bindings on Bifrost.** Bifrost's attribute descriptor model has been a divergence point per `panvk_vX_cmd_draw.c`'s `PANVK_BIFROST_DESC` references. First time we exercise non-zero `VkPipelineVertexInputStateCreateInfo`.
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2. **UBO descriptor binding for vertex stage.** Different from iter4's fragment-stage COMBINED_IMAGE_SAMPLER.
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3. **Vertex-stage descriptor lowering in NIR** (Bifrost-specific code paths).
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4. **Varying interpolation** (color) from vertex output → fragment input.
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5. **UBO data fetch** — does the GPU actually read the matrix from the bound buffer correctly?
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6. **Non-fullscreen rasterization** — partial coverage, edge pixels, anti-aliased-or-not boundaries on Bifrost's tile binner.
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## In-scope (LOCKED 2026-05-19 for iter5)
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- 1 vertex buffer (3 verts), interleaved pos+color, 32-byte stride.
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- 1 UBO (64 bytes, mat4).
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- 1 descriptor set with 1 UBO binding bound to vertex stage.
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- Triangle in NDC, scaled by 0.8 via UBO matrix.
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- 4-point pixel-level verification + range-bound coverage count.
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## Out-of-scope (LOCKED 2026-05-19 for iter5)
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- Index buffer / `vkCmdDrawIndexed`.
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- Multiple draws.
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- Push constants.
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- Texture sampling (iter4 already covered).
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- Depth / stencil.
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- Blending (clear=opaque-black, triangle has α=1).
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- MSAA.
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- Compressed formats.
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- Mipmaps.
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- Real workloads (vkcube/vkmark/Zink) — that's iter6+.
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## Reference
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- Prior closes: [iter1](phase8_iteration1_close.md), [iter2](phase8_iteration2_close.md), [iter3](phase8_iteration3_close.md), [iter4](phase8_iteration4_close.md).
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