reference renderer work

[hoffstadt]

Purpose

The purpose of this pull request (PR) is to support efforts towards a 1.0 reference renderer. These contributions cover several areas including fixes, improvements, and new features.

Deferred + Forward Physics Based Renderer Implementation

With this PR, the reference renderer now uses a forward rendering pass for transparent and more complex materials (clear coat, iridescent, etc.). For opaque objects a deferred rendering technique is used. Both pipelines are physics-based rendering and support image-based lighting.

Skinning Operation were moved to compute shaders

Prior to this PR, skinning was performed in the pixel shader. This required additional shader permutations for skinned vs nonskinned meshes. It also duplicated the skinning operations if skinned meshes were used in multiple passes. Now, compute shaders are run once per pass for skinned meshes.

Current Frame Graph

With the changes of this PR, the current frame graph looks like the following:

Misc.

Increased the allowable bind groups per compute shader

Prior to this PR, compute shaders were only allowed a single bind group. Now they are allowed up to 3 + a dynamic binding identical to the system used for graphics shaders.

Exposed sampler mipmap filtering mode

Prior to this PR, the mipmap filtering mode of samplers were set to NEAREST. Now the filtering mode is a field in the sampler description used to create samplers.

Improved Metal backend's method for ensuring heap residency

Prior to this PR, before draw calls & dispatches were executed, every heap was made resident. With the improvements included here, only the necessary heaps for the current work are made resident. Further improvements will be made in this area.

Fixed Metal backend's copy buffer to texture function

An issue was discovered and fixed where specifying a textures mip & array levels were ignoring.

Fixed Metal backend's create compute shader function

An issue was discovered and fixed where a compute shaders entry function override was ignored.

Future Reference Renderer Work

• reimplement clear coat materials
• reimplement iridescent materials
• reimplement specular-glossiness definied materials
• reimplement index of fraction
• reimplement sheen materials
• reimplement anisotropic materials
• reimplement shadows
• implement decals
• reimplement highlighting & pixel perfect picking
• reimplement morphing
• reimplement shader hot reload
• reimplement shader debug mode