New binding model

[Try]

Research ticket for better binding model. As feedback of work on opengothic, it seem descriptor-set based is way to expensive and error-prone: need something convenient+lighter.

Current idea: push-descriptor + bindless-arrays.

layout(binding = L_Ibo,      std430) readonly buffer Ibo  { uint    indexes [];    } ibo[]; // bindless-array
layout(binding = L_Vbo,      std430) readonly buffer Vbo  { float   vertices[];    } vbo[]; // bindless-array
layout(binding = L_Diffuse)          uniform  texture2D textureMain[]; // bindless-array
layout(binding = L_Sampler)          uniform  sampler   samplerMain;   // push-descriptor
layout(binding = L_SceneClr)         uniform  sampler2D sceneColor;    // push-descriptor
layout(binding = L_GDepth  )         uniform  sampler2D gbufferDepth;  // push-descriptor

Possible C++ interface

const DescriptorArray<Texture2D>& texture = ...
cmd.setBinding(L_Diffuse, texture);
cmd.setBinding(L_SceneClr, sceneColor);
cmd.setPipeline(pso);

or

const DescriptorArray<Texture2D>& texture = ...
cmd.binding = BindingTable(); // clear bindings
cmd.binding[L_Diffuse]  = &texture;
cmd.binding[L_SceneClr] = &sceneColor;
cmd.setPipeline(pso);

Metal

Generally 'it just works': bindless-array can be represented as argument-buffer.

DX12

Root-descriptor + Heap-offset: Root-parameters in DX consists of 64*DWORD (256 bytes of data): root-descriptor is 2 words long, gives 32 descriptors max (and 16, if reserve 128 bytes for push-constant) samplers (non-static) has to be in heap, however combination of possible samplers is limited, can push offset for each array can be allocated in heap, requires 1 DWORD to represent offset

Vulkan

VK_KHR_push_descriptor seem to be closes analog to root-descriptors, and now core in vulkan. VkPhysicalDevicePushDescriptorProperties::maxPushDescriptors == 32 Bindless data can be moved to other descriptor set (however it will break tooling)

TODO:

• [ ] Fix potential bug in setting mip of emulated atomic-imge
• [x] Metal: residency cache
• [x] Adjust Dx12 internal shaders
• [ ] Redirect DX samplers into dedicated heap offsets
• [ ] Inline DX12 CBV in root signature
• [ ] Deduplicate pipelineLayouts/root-signatures, and leverage push/descriptor compatibilities more
• [ ] DX: resizable resources heap?