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.
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.
The Broadcom Videocore IV needs a couple of operations to happen in shader code that might have fixed function hardware on other platforms.
These are:
- writing stencil state setup register
- writing depth value to depth buffer
- performing blending in software
- writing vertex parameter memory read and write setup registers
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.
This means that regardless of what
- depth write state
- blending state
- stencil state
- vertex attribute state
is passed to the driver, this will not be reflected in the final behaviour unless the developer adds it to the assembly shaders.
Helper functionality will be provided to aid with encoding register values. Additionally, general documentation will be provided on how to perform these operations.
This will enable developers to take full control and optimise shaders to the last cycle.
