Describe the binding model differences in READMEs

Author: kvark

src/backend/dx11/README.md

@@ -8,6 +8,16 @@ Render | Depth | Texture
 -------|-------|--------
 ![render_coordinates](../../../info/gl_render_coordinates.png) | ![depth_coordinates](../../../info/dx_depth_coordinates.png) | ![texture_coordinates](../../../info/dx_texture_coordinates.png)
 
+## Binding Model
+
+Writable storage bindings:
+  1. Binding: 0 .. `D3D11_PS_CS_UAV_REGISTER_COUNT`
+
+Other bindings:
+  1. Shader stage: vs, fs, cs
+  2. Register: constant buffers (CBV), shader resources (SRV), samplers
+  3. Binding (tight)
+
 ## Mirroring
 
 TODO

src/backend/dx12/README.md

@@ -8,6 +8,12 @@ Render | Depth | Texture
 -------|-------|--------
 ![render_coordinates](../../../info/gl_render_coordinates.png) | ![depth_coordinates](../../../info/dx_depth_coordinates.png) | ![texture_coordinates](../../../info/dx_texture_coordinates.png)
 
+## Binding Model
+
+Dimensions of the model:
+  1. Space: 0..8
+  2. Binding (tight): constant buffers (CBV), shader resources (SRV), unordered access (UAV), samplers
+
 ## Mirroring
 
 TODO

src/backend/gl/README.md

@@ -4,12 +4,22 @@
 
 Can only be used on non-Apple Unix systems. The WSI is hard-coded to EGL.
 
+Note: the `Instance`, `Surface`, `PhysicalDevice`, `Device`, and `Queue` can only
+have their methods called on the thread where `Instance` was created(!).
+Recording command buffers is free-threaded.
+
 ## Normalized Coordinates
 
 Render | Depth | Texture
 -------|-------|--------
 ![render_coordinates](../../../info/gl_render_coordinates.png) | ![depth_coordinates](../../../info/gl_depth_coordinates.png) | ![texture_coordinates](../../../info/gl_texture_coordinates.png)
 
+## Binding Model
+
+Dimensions of the model:
+  1. Register type: uniform buffers, storage buffers, and combined texture-samplers
+  2. Binding slot (0 .. `MAX_COMBINED_TEXTURE_IMAGE_UNITS` for textures)
+
 ## GLSL Mirroring
 
 Texture Kind | GLSL sampler

src/backend/metal/README.md

@@ -8,6 +8,13 @@ Render | Depth | Texture
 -------|-------|--------
 ![render_coordinates](../../../info/gl_render_coordinates.png) | ![depth_coordinates](../../../info/dx_depth_coordinates.png) | ![texture_coordinates](../../../info/dx_texture_coordinates.png)
 
+## Binding Model
+
+Dimensions of the model:
+  1. Shader stage: vs, fs, cs
+  2. Register: buffers, textures, samplers
+  3. Binding: 0..31 buffers, 0..128 textures, 0..16 samplers
+
 ## Mirroring
 
 TODO

src/backend/vulkan/README.md

@@ -8,6 +8,13 @@ Render | Depth | Texture
 -------|-------|--------
 ![render_coordinates](../../../info/vk_render_coordinates.png) | ![depth_coordinates](../../../info/dx_depth_coordinates.png) | ![texture_coordinates](../../../info/dx_texture_coordinates.png)
 
+## Binding Model
+
+Dimensions of the model:
+  1. Shader stage: vs, fs, cs, others
+  2. Descriptor set: 0 .. `max_bound_descriptor_sets`
+  3. Binding: sparse, but expected to be somewhat tight
+
 ## Mirroring
 
 HAL is modelled after Vulkan, so everything should be 1:1.

src/backend/webgpu/README.md

@@ -8,6 +8,13 @@ Currently requires to be compiled with the `web_sys_unstable_apis` flag.
 RUSTFLAGS=--cfg=web_sys_unstable_apis cargo build --target wasm32-unknown-unknown
 ```
 
+## Binding Model
+
+Dimensions of the model:
+  1. Shader stage: vs, fs, cs
+  2. Resource group: 0 .. 4
+  3. Binding: semi-sparse
+
 ## Normalized Coordinates
 
 Render | Depth | Texture