Don't use structs for uniforms

src/renderer.zig

@@ -13,23 +13,11 @@ const primitives = @import("./primitives.zig");
 const VertexData = primitives.VertexData;
 const PrimitiveData = primitives.PrimitiveData;
 
-/// Holds information about how a perticular scene should be rendered.
-const SceneUniformBuffer = struct {
-    view_proj_matrix: Mat,
-};
-
-/// Holds information about where and how an object should be rendered.
-const ObjectUniformBuffer = struct {
-    model_matrix: Mat,
-    color: [3]f32,
-};
-
 /// Holds data needed to render an object in a rendering pass.
 const ObjectData = struct {
-    /// Reference to data stored on the GPU of type `ObjectUniformBuffer`.
+    /// Bind group which associates model-related buffers with parameters
-    uniform_buffer: *gpu.Buffer,
+    /// in our shader. This one is accessible via `@group(1)` in our shader.
-    /// Bind group used to associate the buffer to the `object` shader parameter.
+    model_bind_group: *gpu.BindGroup,
-    uniform_bind_group: *gpu.BindGroup,
     /// Reference to the primitive (shape or model) to render for this object.
     primitive: *PrimitiveData,
 };
@@ -39,8 +27,8 @@ const Renderer = @This();
 app: *App,
 
 pipeline: *gpu.RenderPipeline,
-scene_uniform_buffer: *gpu.Buffer,
+view_proj_buffer: *gpu.Buffer,
-scene_uniform_bind_group: *gpu.BindGroup,
+camera_bind_group: *gpu.BindGroup,
 
 depth_texture: ?*gpu.Texture = null,
 depth_texture_view: ?*gpu.TextureView = null,
@@ -85,10 +73,16 @@ pub fn init(app: *App) !*Renderer {
     });
 
     // Set up scene related uniform buffers and bind groups.
-    const scene_uniform = createAndWriteUniformBuffer(
+    const view_proj_buffer = createAndWriteBuffer(zm.Mat, &.{zm.identity()}, .{ .copy_dst = true, .uniform = true });
-        pipeline.getBindGroupLayout(0),
+
-        SceneUniformBuffer{ .view_proj_matrix = zm.identity() },
+    // "Bind groups" are used to associate data from buffers with shader parameters.
-    );
+    // So for example the `camera_bind_group` is accessible via `@group(0)` in our shader.
+    const camera_bind_group = core.device.createBindGroup(&gpu.BindGroup.Descriptor.init(.{
+        .layout = pipeline.getBindGroupLayout(0),
+        .entries = &.{
+            gpu.BindGroup.Entry.buffer(0, view_proj_buffer, 0, @sizeOf(zm.Mat)),
+        },
+    }));
 
     // Set up the primitives we want to render.
     //
@@ -128,19 +122,25 @@ pub fn init(app: *App) !*Renderer {
 
         // Make the object have a color depending on its location in the grid.
         // These values are layed out so each corner is red, green, blue and black.
-        const color = .{
+        const model_color = .{
             std.math.clamp(1.0 - x - z, 0.0, 1.0),
             std.math.clamp(x - z, 0.0, 1.0),
             std.math.clamp(z - x, 0.0, 1.0),
         };
 
-        const object_uniform = createAndWriteUniformBuffer(
+        const model_matrix_buffer = createAndWriteBuffer(zm.Mat, &.{zm.transpose(model_matrix)}, .{ .copy_dst = true, .uniform = true });
-            pipeline.getBindGroupLayout(1),
+        defer model_matrix_buffer.release();
-            ObjectUniformBuffer{
+
-                .model_matrix = zm.transpose(model_matrix),
+        const model_color_buffer = createAndWriteBuffer([3]f32, &.{model_color}, .{ .copy_dst = true, .uniform = true });
-                .color = color,
+        defer model_color_buffer.release();
+
+        const model_bind_group = core.device.createBindGroup(&gpu.BindGroup.Descriptor.init(.{
+            .layout = pipeline.getBindGroupLayout(1),
+            .entries = &.{
+                gpu.BindGroup.Entry.buffer(0, model_matrix_buffer, 0, @sizeOf(zm.Mat)),
+                gpu.BindGroup.Entry.buffer(1, model_color_buffer, 0, @sizeOf([3]f32)),
             },
-        );
+        }));
 
         // Pick a "random" primitive to use for this object.
         const primitive_index = app.random.int(usize) % primitive_data.len;
@@ -149,8 +149,7 @@ pub fn init(app: *App) !*Renderer {
         // The `*object` syntax gets us a pointer to each element in the
         // `object_data` slice, allowing us to override it within the loop.
         object.* = .{
-            .uniform_buffer = object_uniform.buffer,
+            .model_bind_group = model_bind_group,
-            .uniform_bind_group = object_uniform.bind_group,
             .primitive = primitive,
         };
     }
@@ -159,8 +158,8 @@ pub fn init(app: *App) !*Renderer {
     result.* = .{
         .app = app,
         .pipeline = pipeline,
-        .scene_uniform_buffer = scene_uniform.buffer,
+        .view_proj_buffer = view_proj_buffer,
-        .scene_uniform_bind_group = scene_uniform.bind_group,
+        .camera_bind_group = camera_bind_group,
         .primitive_data = primitive_data,
         .object_data = object_data,
     };
@@ -178,8 +177,8 @@ pub fn deinit(self: *Renderer) void {
     defer self.app.allocator.destroy(self);
 
     defer self.pipeline.release();
-    defer self.scene_uniform_buffer.release();
+    defer self.view_proj_buffer.release();
-    defer self.scene_uniform_bind_group.release();
+    defer self.camera_bind_group.release();
 
     defer self.app.allocator.free(self.primitive_data);
     defer for (self.primitive_data) |p| {
@@ -188,8 +187,7 @@ pub fn deinit(self: *Renderer) void {
     };
     defer self.app.allocator.free(self.object_data);
     defer for (self.object_data) |o| {
-        o.uniform_buffer.release();
+        o.model_bind_group.release();
-        o.uniform_bind_group.release();
     };
 
     defer if (self.depth_texture) |t| t.release();
@@ -249,11 +247,11 @@ pub fn update(self: *Renderer) void {
     defer encoder.release();
 
     // Write to the scene uniform buffer for this set of commands.
-    encoder.writeBuffer(self.scene_uniform_buffer, 0, &[_]SceneUniformBuffer{.{
+    encoder.writeBuffer(self.view_proj_buffer, 0, &[_]zm.Mat{
         // All matrices the GPU has to work with need to be transposed,
         // because WebGPU uses column-major matrices while zmath is row-major.
-        .view_proj_matrix = zm.transpose(view_proj_matrix),
+        zm.transpose(view_proj_matrix),
-    }});
+    });
 
     {
         const pass = encoder.beginRenderPass(&render_pass_info);
@@ -261,17 +259,17 @@ pub fn update(self: *Renderer) void {
         defer pass.end();
 
         pass.setPipeline(self.pipeline);
-        pass.setBindGroup(0, self.scene_uniform_bind_group, &.{});
+        pass.setBindGroup(0, self.camera_bind_group, &.{});
 
         for (self.object_data) |object| {
-            // Set the vertex and index buffer used to render this object
+            // Set the vertex and index buffer used to render this
-            // to the primitive it wants to use (either triangle or square).
+            // object to the ones from the primitive it wants to use.
             const prim = object.primitive;
             pass.setVertexBuffer(0, prim.vertex_buffer, 0, prim.vertex_count * @sizeOf(VertexData));
             pass.setIndexBuffer(prim.index_buffer, .uint32, 0, prim.index_count * @sizeOf(u32));
 
-            // Set the bind group for an object we want to render.
+            // Set the bind group for the object we want to render.
-            pass.setBindGroup(1, object.uniform_bind_group, &.{});
+            pass.setBindGroup(1, object.model_bind_group, &.{});
 
             // Draw a number of triangles as specified in the index buffer.
             pass.drawIndexed(prim.index_count, 1, 0, 0, 0);
@@ -302,30 +300,6 @@ pub fn recreateDepthTexture(self: *Renderer) void {
     self.depth_texture_view = self.depth_texture.?.createView(null);
 }
 
-/// Creates a buffer on the GPU to store uniform parameter information as
-/// well as a bind group with the specified layout pointing to that buffer.
-/// Additionally, immediately fills the buffer with the provided data.
-pub fn createAndWriteUniformBuffer(
-    layout: *gpu.BindGroupLayout,
-    data: anytype,
-) struct {
-    buffer: *gpu.Buffer,
-    bind_group: *gpu.BindGroup,
-} {
-    const T = @TypeOf(data);
-    const usage = gpu.Buffer.UsageFlags{ .copy_dst = true, .uniform = true };
-    const buffer = createAndWriteBuffer(T, &.{data}, usage);
-
-    // "Bind groups" are used to associate data from buffers with shader parameters.
-    // So for example the `scene_uniform_bind_group` is accessible via `scene` in our shader.
-    // Essentially, buffer = data, and bind group = binding parameter to that data.
-    const bind_group_entry = gpu.BindGroup.Entry.buffer(0, buffer, 0, @sizeOf(T));
-    const bind_group_desc = gpu.BindGroup.Descriptor.init(.{ .layout = layout, .entries = &.{bind_group_entry} });
-    const bind_group = core.device.createBindGroup(&bind_group_desc);
-
-    return .{ .buffer = buffer, .bind_group = bind_group };
-}
-
 /// Creates a buffer on the GPU with the specified usage
 /// flags and immediately fills it with the provided data.
 pub fn createAndWriteBuffer(

src/shader.wgsl

@@ -1,14 +1,7 @@
-struct SceneUniformBuffer {
+@group(0) @binding(0) var<uniform> view_proj_matrix: mat4x4<f32>;
-    view_proj_matrix: mat4x4<f32>,
-};
-
-struct ObjectUniformBuffer {
-    model_matrix: mat4x4<f32>,
-    color: vec3<f32>,
-};
 
-@group(0) @binding(0) var<uniform> scene: SceneUniformBuffer;
+@group(1) @binding(0) var<uniform> model_matrix: mat4x4<f32>;
-@group(1) @binding(0) var<uniform> object: ObjectUniformBuffer;
+@group(1) @binding(1) var<uniform> model_color: vec3<f32>;
 
 struct VertexInput {
     @location(0) position: vec3<f32>,
@@ -25,9 +18,9 @@ struct FragmentOutput {
 
 @vertex fn vertex_main(in: VertexInput) -> VertexOutput {
     var out: VertexOutput;
-    let mvp = object.model_matrix * scene.view_proj_matrix;
+    let mvp = model_matrix * view_proj_matrix;
     out.position = vec4<f32>(in.position, 1.0) * mvp;
-    out.color    = vec4<f32>(object.color, 1.0);
+    out.color    = vec4<f32>(model_color, 1.0);
     return out;
 }