Replace StateCaches by explicit PSO

[paroj]

Pipeline state

• [ ] Dynamic state
• [ ] Shaders
• [x] Blend State
• [ ] Pipeline layout
• [ ] Rasterizer state
• [ ] Vertex input
• [ ] Depth/stencil state
• [ ] Input assembly
• [ ] Render pass

references

• https://www.khronos.org/assets/uploads/developers/library/2016-vulkan-devday-uk/10-Porting-to-Vulkan.pdf
• https://software.intel.com/en-us/blogs/2014/07/23/direct3d-12-overview-part-2-pipeline-state-object
• https://docs.microsoft.com/en-us/windows/desktop/direct3d12/managing-graphics-pipeline-state-in-direct3d-12

[paroj]

PSOs still need caching: https://www.khronos.org/registry/vulkan/specs/1.1-extensions/man/html/vkCreatePipelineCache.html

[paroj]

also they are required for Metal (citing Matias):

D3D11 & GL drivers implement this for you internally, and usually they offload the cache to a secondary thread to hide the latency. They implement the caches inside DrawPrimitive calls. So Ogre that means the right place to place the PSO cache is in MetalRenderSystem::_render(const RenderOperation& op)

[paroj]

maybe resurrect this for D3D11: https://bitbucket.org/sinbad/ogre/pull-requests/701/direct3d11-caching-of-render-state-objects/diff