improve shader import model (#5703)

# Objective

operate on naga IR directly to improve handling of shader modules.
- give codespan reporting into imported modules
- allow glsl to be used from wgsl and vice-versa

the ultimate objective is to make it possible to 
- provide user hooks for core shader functions (to modify light
behaviour within the standard pbr pipeline, for example)
- make automatic binding slot allocation possible

but ... since this is already big, adds some value and (i think) is at
feature parity with the existing code, i wanted to push this now.

## Solution

i made a crate called naga_oil (https://github.com/robtfm/naga_oil -
unpublished for now, could be part of bevy) which manages modules by
- building each module independantly to naga IR
- creating "header" files for each supported language, which are used to
build dependent modules/shaders
- make final shaders by combining the shader IR with the IR for imported
modules

then integrated this into bevy, replacing some of the existing shader
processing stuff. also reworked examples to reflect this.

## Migration Guide

shaders that don't use `#import` directives should work without changes.

the most notable user-facing difference is that imported
functions/variables/etc need to be qualified at point of use, and
there's no "leakage" of visible stuff into your shader scope from the
imports of your imports, so if you used things imported by your imports,
you now need to import them directly and qualify them.

the current strategy of including/'spreading' `mesh_vertex_output`
directly into a struct doesn't work any more, so these need to be
modified as per the examples (e.g. color_material.wgsl, or many others).
mesh data is assumed to be in bindgroup 2 by default, if mesh data is
bound into bindgroup 1 instead then the shader def `MESH_BINDGROUP_1`
needs to be added to the pipeline shader_defs.

Author: robtfm

assets/shaders/animate_shader.wgsl

@@ -1,6 +1,6 @@
-#import bevy_pbr::mesh_types
 // The time since startup data is in the globals binding which is part of the mesh_view_bindings import
-#import bevy_pbr::mesh_view_bindings
+#import bevy_pbr::mesh_view_bindings globals
+#import bevy_pbr::mesh_vertex_output MeshVertexOutput
 
 fn oklab_to_linear_srgb(c: vec3<f32>) -> vec3<f32> {
     let L = c.x;
@@ -22,12 +22,8 @@ fn oklab_to_linear_srgb(c: vec3<f32>) -> vec3<f32> {
     );
 }
 
-struct FragmentInput {
-    #import bevy_pbr::mesh_vertex_output
-}
-
 @fragment
-fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
+fn fragment(in: MeshVertexOutput) -> @location(0) vec4<f32> {
     let speed = 2.0;
     // The globals binding contains various global values like time
     // which is the time since startup in seconds

assets/shaders/array_texture.wgsl

@@ -1,60 +1,51 @@
-#import bevy_pbr::mesh_view_bindings
-#import bevy_pbr::mesh_bindings
-
-#import bevy_pbr::pbr_types
-#import bevy_pbr::utils
-#import bevy_pbr::clustered_forward
-#import bevy_pbr::lighting
-#import bevy_pbr::shadows
-#import bevy_pbr::fog
-#import bevy_pbr::pbr_functions
-#import bevy_pbr::pbr_ambient
+#import bevy_pbr::mesh_vertex_output    MeshVertexOutput
+#import bevy_pbr::mesh_view_bindings    view
+#import bevy_pbr::pbr_types             STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT
+#import bevy_core_pipeline::tonemapping tone_mapping
+#import bevy_pbr::pbr_functions as fns
 
 @group(1) @binding(0)
 var my_array_texture: texture_2d_array<f32>;
 @group(1) @binding(1)
 var my_array_texture_sampler: sampler;
 
-struct FragmentInput {
-    @builtin(front_facing) is_front: bool,
-    @builtin(position) frag_coord: vec4<f32>,
-    #import bevy_pbr::mesh_vertex_output
-};
-
 @fragment
-fn fragment(in: FragmentInput) -> @location(0) vec4<f32> {
-    let layer = i32(in.world_position.x) & 0x3;
+fn fragment(
+    @builtin(front_facing) is_front: bool,
+    mesh: MeshVertexOutput,
+) -> @location(0) vec4<f32> {
+    let layer = i32(mesh.world_position.x) & 0x3;
 
     // Prepare a 'processed' StandardMaterial by sampling all textures to resolve
     // the material members
-    var pbr_input: PbrInput = pbr_input_new();
+    var pbr_input: fns::PbrInput = fns::pbr_input_new();
 
-    pbr_input.material.base_color = textureSample(my_array_texture, my_array_texture_sampler, in.uv, layer);
+    pbr_input.material.base_color = textureSample(my_array_texture, my_array_texture_sampler, mesh.uv, layer);
 #ifdef VERTEX_COLORS
-    pbr_input.material.base_color = pbr_input.material.base_color * in.color;
+    pbr_input.material.base_color = pbr_input.material.base_color * mesh.color;
 #endif
 
-    pbr_input.frag_coord = in.frag_coord;
-    pbr_input.world_position = in.world_position;
-    pbr_input.world_normal = prepare_world_normal(
-        in.world_normal,
+    pbr_input.frag_coord = mesh.position;
+    pbr_input.world_position = mesh.world_position;
+    pbr_input.world_normal = fns::prepare_world_normal(
+        mesh.world_normal,
         (pbr_input.material.flags & STANDARD_MATERIAL_FLAGS_DOUBLE_SIDED_BIT) != 0u,
-        in.is_front,
+        is_front,
     );
 
     pbr_input.is_orthographic = view.projection[3].w == 1.0;
 
-    pbr_input.N = apply_normal_mapping(
+    pbr_input.N = fns::apply_normal_mapping(
         pbr_input.material.flags,
-        pbr_input.world_normal,
+        mesh.world_normal,
 #ifdef VERTEX_TANGENTS
 #ifdef STANDARDMATERIAL_NORMAL_MAP
-        in.world_tangent,
+        mesh.world_tangent,
 #endif
 #endif
-        in.uv,
+        mesh.uv,
     );
-    pbr_input.V = calculate_view(in.world_position, pbr_input.is_orthographic);
+    pbr_input.V = fns::calculate_view(mesh.world_position, pbr_input.is_orthographic);
 
-    return tone_mapping(pbr(pbr_input));
+    return tone_mapping(fns::pbr(pbr_input), view.color_grading);
 }

assets/shaders/cubemap_unlit.wgsl

@@ -1,4 +1,4 @@
-#import bevy_pbr::mesh_view_bindings
+#import bevy_pbr::mesh_vertex_output MeshVertexOutput
 
 #ifdef CUBEMAP_ARRAY
 @group(1) @binding(0)
@@ -13,9 +13,9 @@ var base_color_sampler: sampler;
 
 @fragment
 fn fragment(
-    #import bevy_pbr::mesh_vertex_output
+    mesh: MeshVertexOutput,
 ) -> @location(0) vec4<f32> {
-    let fragment_position_view_lh = world_position.xyz * vec3<f32>(1.0, 1.0, -1.0);
+    let fragment_position_view_lh = mesh.world_position.xyz * vec3<f32>(1.0, 1.0, -1.0);
     return textureSample(
         base_color_texture,
         base_color_sampler,

assets/shaders/custom_gltf_2d.wgsl

@@ -1,6 +1,6 @@
-#import bevy_sprite::mesh2d_view_bindings
-#import bevy_sprite::mesh2d_bindings
-#import bevy_sprite::mesh2d_functions
+#import bevy_sprite::mesh2d_view_bindings   globals
+#import bevy_sprite::mesh2d_bindings        mesh
+#import bevy_sprite::mesh2d_functions       mesh2d_position_local_to_clip
 
 struct Vertex {
     @location(0) position: vec3<f32>,

assets/shaders/custom_material.frag

@@ -10,7 +10,11 @@ layout(set = 1, binding = 0) uniform CustomMaterial {
 layout(set = 1, binding = 1) uniform texture2D CustomMaterial_texture;
 layout(set = 1, binding = 2) uniform sampler CustomMaterial_sampler;
 
+// wgsl modules can be imported and used in glsl
+// FIXME - this doesn't work any more ...
+// #import bevy_pbr::pbr_functions as PbrFuncs
 
 void main() {
+    // o_Target = PbrFuncs::tone_mapping(Color * texture(sampler2D(CustomMaterial_texture,CustomMaterial_sampler), v_Uv));
     o_Target = Color * texture(sampler2D(CustomMaterial_texture,CustomMaterial_sampler), v_Uv);
 }

assets/shaders/custom_material.wgsl

@@ -1,3 +1,5 @@
+#import bevy_pbr::mesh_vertex_output MeshVertexOutput
+
 struct CustomMaterial {
     color: vec4<f32>,
 };
@@ -11,7 +13,7 @@ var base_color_sampler: sampler;
 
 @fragment
 fn fragment(
-    #import bevy_pbr::mesh_vertex_output
+    mesh: MeshVertexOutput,
 ) -> @location(0) vec4<f32> {
-    return material.color * textureSample(base_color_texture, base_color_sampler, uv);
+    return material.color * textureSample(base_color_texture, base_color_sampler, mesh.uv);
 }

assets/shaders/custom_material_screenspace_texture.wgsl

@@ -1,5 +1,6 @@
-#import bevy_pbr::mesh_view_bindings
-#import bevy_pbr::utils
+#import bevy_pbr::mesh_view_bindings  view
+#import bevy_pbr::mesh_vertex_output  MeshVertexOutput
+#import bevy_pbr::utils               coords_to_viewport_uv
 
 @group(1) @binding(0)
 var texture: texture_2d<f32>;
@@ -8,10 +9,9 @@ var texture_sampler: sampler;
 
 @fragment
 fn fragment(
-    @builtin(position) position: vec4<f32>,
-    #import bevy_pbr::mesh_vertex_output
+    mesh: MeshVertexOutput,
 ) -> @location(0) vec4<f32> {
-    let viewport_uv = coords_to_viewport_uv(position.xy, view.viewport);
+    let viewport_uv = coords_to_viewport_uv(mesh.position.xy, view.viewport);
     let color = textureSample(texture, texture_sampler, viewport_uv);
     return color;
 }

assets/shaders/custom_vertex_attribute.wgsl

@@ -1,15 +1,12 @@
-#import bevy_pbr::mesh_view_bindings
-#import bevy_pbr::mesh_bindings
+#import bevy_pbr::mesh_bindings   mesh
+#import bevy_pbr::mesh_functions  mesh_position_local_to_clip
 
 struct CustomMaterial {
     color: vec4<f32>,
 };
 @group(1) @binding(0)
 var<uniform> material: CustomMaterial;
 
-// NOTE: Bindings must come before functions that use them!
-#import bevy_pbr::mesh_functions
-
 struct Vertex {
     @location(0) position: vec3<f32>,
     @location(1) blend_color: vec4<f32>,
@@ -23,7 +20,10 @@ struct VertexOutput {
 @vertex
 fn vertex(vertex: Vertex) -> VertexOutput {
     var out: VertexOutput;
-    out.clip_position = mesh_position_local_to_clip(mesh.model, vec4<f32>(vertex.position, 1.0));
+    out.clip_position = mesh_position_local_to_clip(
+        mesh.model,
+        vec4<f32>(vertex.position, 1.0)
+    );
     out.blend_color = vertex.blend_color;
     return out;
 }

assets/shaders/instancing.wgsl

@@ -1,11 +1,5 @@
-#import bevy_pbr::mesh_types
-#import bevy_pbr::mesh_view_bindings
-
-@group(1) @binding(0)
-var<uniform> mesh: Mesh;
-
-// NOTE: Bindings must come before functions that use them!
-#import bevy_pbr::mesh_functions
+#import bevy_pbr::mesh_functions  mesh_position_local_to_clip
+#import bevy_pbr::mesh_bindings   mesh
 
 struct Vertex {
     @location(0) position: vec3<f32>,
@@ -25,7 +19,10 @@ struct VertexOutput {
 fn vertex(vertex: Vertex) -> VertexOutput {
     let position = vertex.position * vertex.i_pos_scale.w + vertex.i_pos_scale.xyz;
     var out: VertexOutput;
-    out.clip_position = mesh_position_local_to_clip(mesh.model, vec4<f32>(position, 1.0));
+    out.clip_position = mesh_position_local_to_clip(
+        mesh.model, 
+        vec4<f32>(position, 1.0)
+    );
     out.color = vertex.i_color;
     return out;
 }

assets/shaders/line_material.wgsl

@@ -1,3 +1,5 @@
+#import bevy_pbr::mesh_vertex_output MeshVertexOutput
+
 struct LineMaterial {
     color: vec4<f32>,
 };
@@ -7,7 +9,7 @@ var<uniform> material: LineMaterial;
 
 @fragment
 fn fragment(
-    #import bevy_pbr::mesh_vertex_output
+    mesh: MeshVertexOutput,
 ) -> @location(0) vec4<f32> {
     return material.color;
 }