now vulkan can do screenshots too. however, it depends on blits being
available between swapchain and rgba8 formats, so if it's not the case
for some reason, the resulting image will have mixed components.
after we've updated how brush index buffer references vertices to allow
for draw call coalescing ray tracing broke on amd.
this is because amd cards expect a correct value in
VkAccelerationStructureGeometryTrianglesDataKHR::maxVertex. make sure we
fill a correct value there.
make all geoms share the same constant vertex offset so that continuous indices can be exploited to generate only a single draw call for a group of geometries with the same texture
from: Mark Jarzynski and Marc Olano, Hash Functions for GPU Rendering, Journal of Computer Graphics Techniques (JCGT), vol. 9, no. 3, 21-38, 2020
http://www.jcgt.org/published/0009/03/02/
this is mostly copied from ray tracing gems 2 chapter 7 (Texture Coordinate Gradients Estimation for Ray Cones, by Wessam Bahnassi).
There's a weird bit about radians vs degrees. We'll figure it out later when the book becomes available.
this is very proof-of-concept quality. it should be definitely done some other way
e.g. we should control reflectivity and transparency differently (and not together)
and they should be based on texture ids, not on render_mode
it's also unfortunate that transparency required a lot of bounces. we should probably control transparency bounces separately from light bounces.
alternatively, transparency effects (beams, sprites) should be done with custom intersection shaders and not based on transparent geometry
We used to dispatch rays anyway even if there was no models to render and tlas wasn't built (which is the case for the first few frames).
This ended up crashing AMD gpu when using some (but not all) variants of rgen shaders.
With this change we'll check for whether there are any models to render, and if there are none, then we'll just clear frame to black.
This change also refactors ray tracing a bit.
