How can I tell what Set and Binding to Use for Shader Uniforms?

[zicklag]

In my custom GLSL shader I have a section like this for the uniforms:

layout(set = 0, binding = 0) uniform Camera {
    mat4 ViewProj;
};
layout(set = 1, binding = 0) uniform Transform {
    mat4 Model;
};
layout(set = 2, binding = 0) uniform LdtkTilemapMaterial_scale {
    float map_scale;
};
layout(set = 2, binding = 1) uniform LdtkTilemapMaterial_map_info {
    uint map_width_tiles;
    uint map_height_tiles;
    uint layer_index;
};
layout(set = 2, binding = 2) uniform LdtkTilemapMaterial_tileset_info {
    uint tileset_width_tiles;
    uint tileset_height_tiles;
    uint tileset_grid_size;
};
layout(set = 2, binding = 3) uniform texture2D LdtkTilemapMaterial_texture;
layout(set = 2, binding = 4) uniform sampler LdtkTilemapMaterial_texture_sampler;
struct TileInfo {
    uint index;
    uint flip_bits;
};
layout(set = 2, binding = 5) buffer LdtkTilemapMaterial_tiles {
    TileInfo[] map_tiles;
};

I'm trying to understand how to tell, from my Rust code, what the corresponding set and binding values need to be in my shader, according to the differ RenderResources nodes in the pipeline, etc.

For the most part, I got the above example working great, except for the fact that it seems like the Model transform is not being picked up. I decided to check out Bevy's spritesheet shader, and I realized that the uniforms were in a different order!

Somehow the SpriteTransform is in set = 2 and additionally the whole TextureAtlasSprite is in the same set as the Transform, which it had previously looked to me like every struct would be in its own set.

layout(set = 0, binding = 0) uniform Camera {
    mat4 ViewProj;
};

// TODO: merge dimensions into "sprites" buffer when that is supported in the Uniforms derive abstraction
layout(set = 1, binding = 0) uniform TextureAtlas_size {
    vec2 AtlasSize;
};

struct Rect {
    vec2 begin;
    vec2 end;
};

layout(set = 1, binding = 1) buffer TextureAtlas_textures {
    Rect[] Textures;
};


layout(set = 2, binding = 0) uniform Transform {
    mat4 SpriteTransform;
};

layout(set = 2, binding = 1) uniform TextureAtlasSprite {
    vec4 TextureAtlasSprite_color;
    uint TextureAtlasSprite_index;
};

It all seems almost random to me. I don't really mind it being in different orders or anything, but is there any reliable way for me to tell where in the layout these resources are going to end up so that I know how to write my shader?

[zicklag]

Documenting my discoveries so far:

• When deriving RenderResources, the #[render_resources(from_self)] means that the name of the uniform will be the name of the struct with no suffix and each field will be present under that uniform.
• When you dont have from_self specified, each field gets its own uniform that is the struct name suffixed with the field name, and the data inside that field specified under it.
• Bevy parses your shaders to determine the layout definitions inside of them, but I still don't know how it determines which render resources to stick into each set and binding.
• Doing a search for the Transform uniform, it seems that 6 out of 9 times in the shader it is set to set = 1, binding = 0, but the other 3 times it is in set = 2, binding = 0
  
  It seems like maybe it doesn't matter which set a uniform is in and bevy just uses the name of the uniform to figure out which bindings to put the data in.
• I am able to swtich the set for my LdtkTilemapMaterial uniforms and the Transform uniform, putting them in a different order, and they still work.

So far it seems like Bevy uses pretty much just the name of the RenderResource in order to determine which uniform to match it up with automaticallly.

I'm not exactly sure what determines what set you should use. I would have thought that each RenderResource node get's a different set or something, but that doesn't seem to be the case with the Bevy shader above where TextureAtlasSprite is in the same set with Transform for some reason.

[zicklag]

OK, I'm going to go with the conclusion that Bevy just figures it out based on the names. I found out that something else was wong with my Transforms and that's why I wasn't getting any info in the shader there.