mirror of
https://github.com/Yours3lf/rpi-vk-driver.git
synced 2024-12-13 01:08:53 +01:00
125 lines
4.7 KiB
Markdown
125 lines
4.7 KiB
Markdown
# rpi-vk-driver
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(not conformant yet, can't use official name or logo)
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## Milestones
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- [x] clear screen example working
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- [x] triangle example working
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- [x] shader from assembly, vertices from vertex buffer object, no uniforms, color hardcoded
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- [x] uniforms for matrix multiplication and animation
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- [x] texture coordinates and texture sampling
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- [x] varyings
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- [x] Multiple vertex attributes
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- [x] Depth buffers
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- [x] Stencil buffers
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- [x] Indexed draw calls
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- [x] blending
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- [ ] mipmapping
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- [x] Shader compiler chain
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- [x] QPU assembler / disassembler
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- [x] Resources
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- [x] Descriptor support
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- [x] VkSampler support
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- [x] Push constant support
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- [x] Platform features
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- [x] Layer support
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- [ ] Emulated features
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- [ ] Clear command support
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- [ ] Copy command support
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- [ ] Render to texture features
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- [ ] VkRenderPass support
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- [ ] Subpass support
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- [ ] Multiple attachments
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- [ ] MSAA support
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- [ ] Synchronization
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- [ ] vkCmdPipelineBarrier support
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- [ ] Performance
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- [ ] Performance counters
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- [ ] Queries
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- [ ] Shader performance info
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- [ ] WSI
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- [ ] Direct to display support
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- [ ] Secondary command buffers
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- [ ] Fixes
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- [ ] Hardware bug workarounds
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- [ ] Handle offsets wherever required
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- [ ] Handle subresource ranges properly
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- [ ] Handle allocation scopes properly
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- [ ] Shader module creation might not be thread safe
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- [ ] Try to pass as much of the VK CTS as possible with existing feature set
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## VK CTS progress
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- Passed: 7894/67979 (11.6%)
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- Failed: 878/67979 (1.3%)
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- Not supported: 59206/67979 (87.1%)
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- Warnings: 1/67979 (0.0%)
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Conformance run is considered passing if all tests finish with allowed result
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codes.
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Following status
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codes are allowed:
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- Pass
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- NotSupported
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- QualityWarning
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- CompatibilityWarning
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There are about 470.000 conformance tests.
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## FAQ
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### Will this ever be a fully functional VK driver?
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As far as I know the PI is NOT fully VK capable on the hardware level. I can already see that some things will need to be emulated and others won't ever be emulated.
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### What performance should you expect?
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Performance wise, the Pi is quite capable. The specs and architecture is close to the GPU in the iPhone 4s. The only problem I see is bandwidth as you only have about 7GB/s compared to 12-25GB/s on typical mobile phones. So post processing is a huge no and you'd need to be very careful about the techniques that you use. Eg. you'd need to stay on chip at all times.
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CPU performance (eg. number of draw calls) should be enough on the quad-core PIs as you can easily utilise all cores using VK.
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### What features will not be supported?
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- 3D textures
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- sparse textures
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- compute shaders (though could be supported to some extent if the kernel side would support it)
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- some texture formats
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- some render target texture formats
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- occlusion queries (https://github.com/anholt/mesa/wiki/VC4-OpenGL-support)
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- indirect draws
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- spirv shaders
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- events
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- proper semaphore support
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- tessellation shaders
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- geometry shaders
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- 32 bit indices
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- instancing
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- some vertex buffer formats
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- pipeline caches (doesn't make sense with assembly shaders)
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### What additional features will this driver support?
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- I already added support (to be polished) to load shader assembly. This will enable devs to optimise shaders to the last cycle.
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- I'll probably add something to indicate towards the developer that things are emulated or not supported at all.
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- Videocore IV provides some performance counters these will be exposed
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- Videocore IV supports some texture formats that are not present in the spec
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- bw1: 1 bit black and white
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- a4: 4 bit alpha
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- a1: 1 bit alpha
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- vector graphics support?
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### Shader patching
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The Broadcom Videocore IV needs a couple of operations to happen in shader code that might have fixed function hardware on other platforms.
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These are:
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- writing stencil state setup register
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- writing depth value to depth buffer
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- performing blending in software
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- writing vertex parameter memory read and write setup registers
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Since the project will not include a compiler, but rather works with an assembly based shader setup, I decided not to patch shaders based on the state provided to the driver, but rather let the developer have full control.
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This means that regardless of what
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- depth write state
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- blending state
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- stencil state
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- vertex attribute state
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is passed to the driver, this will not be reflected in the final behaviour unless the developer adds it to the assembly shaders.
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Helper functionality will be provided to aid with encoding register values. Additionally, general documentation will be provided on how to perform these operations.
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This will enable developers to take full control and optimise shaders to the last cycle.
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