Render triangles as 3 separate models

src/main.zig

@@ -8,6 +8,14 @@ const Mat = zm.Mat;
 
 const VertexData = struct {
     position: [3]f32,
+};
+
+const SceneUniformBuffer = struct {
+    view_proj_matrix: zm.Mat,
+};
+
+const ModelUniformBuffer = struct {
+    matrix: zm.Mat,
     color: [3]f32,
 };
 
@@ -17,8 +25,10 @@ app_timer: core.Timer,
 title_timer: core.Timer,
 
 pipeline: *gpu.RenderPipeline,
-mvp_uniform_buffer: *gpu.Buffer,
-mvp_bind_group: *gpu.BindGroup,
+scene_uniform_buffer: *gpu.Buffer,
+scene_bind_group: *gpu.BindGroup,
+model_uniform_buffers: [3]*gpu.Buffer,
+model_bind_groups: [3]*gpu.BindGroup,
 vertex_count: u32,
 vertex_buffer: *gpu.Buffer,
 
@@ -42,7 +52,6 @@ pub fn init(app: *App) !void {
                     .step_mode = .vertex,
                     .attributes = &.{
                         .{ .format = .float32x3, .shader_location = 0, .offset = @offsetOf(VertexData, "position") },
-                        .{ .format = .float32x3, .shader_location = 1, .offset = @offsetOf(VertexData, "color") },
                     },
                 }),
             },
@@ -54,36 +63,58 @@ pub fn init(app: *App) !void {
         }),
     });
 
-    // Set up uniform buffer and bind group.
-    app.mvp_uniform_buffer = core.device.createBuffer(&.{
+    // Set up uniform buffers and bind groups.
+
+    // The "scene" uniform contains information for each rendered scene.
+    app.scene_uniform_buffer = core.device.createBuffer(&.{
         .usage = .{ .copy_dst = true, .uniform = true },
-        .size = @sizeOf(zm.Mat),
+        .size = @sizeOf(SceneUniformBuffer),
         .mapped_at_creation = .false,
     });
-
-    app.mvp_bind_group = core.device.createBindGroup(
+    app.scene_bind_group = core.device.createBindGroup(
         &gpu.BindGroup.Descriptor.init(.{
             .layout = app.pipeline.getBindGroupLayout(0),
             .entries = &.{
-                gpu.BindGroup.Entry.buffer(0, app.mvp_uniform_buffer, 0, @sizeOf(zm.Mat)),
+                gpu.BindGroup.Entry.buffer(0, app.scene_uniform_buffer, 0, @sizeOf(SceneUniformBuffer)),
             },
         }),
     );
 
+    // The "model" uniforms contain information about how to render each model.
+    for (0..3) |i| {
+        app.model_uniform_buffers[i] = core.device.createBuffer(&.{
+            .usage = .{ .copy_dst = true, .uniform = true },
+            .size = @sizeOf(ModelUniformBuffer),
+            .mapped_at_creation = .false,
+        });
+        app.model_bind_groups[i] = core.device.createBindGroup(
+            &gpu.BindGroup.Descriptor.init(.{
+                .layout = app.pipeline.getBindGroupLayout(1),
+                .entries = &.{
+                    gpu.BindGroup.Entry.buffer(0, app.model_uniform_buffers[i], 0, @sizeOf(ModelUniformBuffer)),
+                },
+            }),
+        );
+    }
+    // Upload model render information (matrix + color) to the GPU.
+    core.queue.writeBuffer(app.model_uniform_buffers[0], 0, &[_]ModelUniformBuffer{.{
+        .matrix = zm.transpose(zm.translation(-1.0, 0.25, 0.0)),
+        .color = .{ 1.0, 0.0, 0.0 },
+    }});
+    core.queue.writeBuffer(app.model_uniform_buffers[1], 0, &[_]ModelUniformBuffer{.{
+        .matrix = zm.transpose(zm.translation(0.0, -0.25, 0.0)),
+        .color = .{ 0.0, 1.0, 0.0 },
+    }});
+    core.queue.writeBuffer(app.model_uniform_buffers[2], 0, &[_]ModelUniformBuffer{.{
+        .matrix = zm.transpose(zm.translation(1.0, 0.0, 0.0)),
+        .color = .{ 0.0, 0.0, 1.0 },
+    }});
+
     // Set up vertex buffer, containing the vertex data we want to draw.
-    // `vertices` contains three separate triangles, each with a different color.
     const vertices = [_]VertexData{
-        .{ .position = .{ -1.0, 0.5 + 0.25, 0.0 }, .color = .{ 1.0, 0.0, 0.0 } },
-        .{ .position = .{ -1.5, -0.5 + 0.25, 0.0 }, .color = .{ 1.0, 0.0, 0.0 } },
-        .{ .position = .{ -0.5, -0.5 + 0.25, 0.0 }, .color = .{ 1.0, 0.0, 0.0 } },
-
-        .{ .position = .{ 0.0, 0.5 - 0.25, 0.0 }, .color = .{ 0.0, 1.0, 0.0 } },
-        .{ .position = .{ -0.5, -0.5 - 0.25, 0.0 }, .color = .{ 0.0, 1.0, 0.0 } },
-        .{ .position = .{ 0.5, -0.5 - 0.25, 0.0 }, .color = .{ 0.0, 1.0, 0.0 } },
-
-        .{ .position = .{ 1.0, 0.5, 0.0 }, .color = .{ 0.0, 0.0, 1.0 } },
-        .{ .position = .{ 0.5, -0.5, 0.0 }, .color = .{ 0.0, 0.0, 1.0 } },
-        .{ .position = .{ 1.5, -0.5, 0.0 }, .color = .{ 0.0, 0.0, 1.0 } },
+        .{ .position = .{ 0.0, 0.5, 0.0 } },
+        .{ .position = .{ -0.5, -0.5, 0.0 } },
+        .{ .position = .{ 0.5, -0.5, 0.0 } },
     };
     app.vertex_count = vertices.len;
     app.vertex_buffer = core.device.createBuffer(&.{
@@ -100,8 +131,10 @@ pub fn deinit(app: *App) void {
     // in the order they were created in `init`.
     defer core.deinit();
     defer app.pipeline.release();
-    defer app.mvp_uniform_buffer.release();
-    defer app.mvp_bind_group.release();
+    defer app.scene_uniform_buffer.release();
+    defer app.scene_bind_group.release();
+    defer for (app.model_uniform_buffers) |b| b.release();
+    defer for (app.model_bind_groups) |g| g.release();
     defer app.vertex_buffer.release();
 }
 
@@ -151,7 +184,12 @@ pub fn update(app: *App) !bool {
     const encoder = core.device.createCommandEncoder(null);
     defer encoder.release();
 
-    encoder.writeBuffer(app.mvp_uniform_buffer, 0, &[_]zm.Mat{zm.transpose(view_proj_matrix)});
+    // Write to the scene uniform buffer for this set of commands.
+    encoder.writeBuffer(app.scene_uniform_buffer, 0, &[_]SceneUniformBuffer{.{
+        // 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),
+    }});
 
     {
         const pass = encoder.beginRenderPass(&render_pass_info);
@@ -159,11 +197,15 @@ pub fn update(app: *App) !bool {
         defer pass.end();
 
         pass.setPipeline(app.pipeline);
-        pass.setBindGroup(0, app.mvp_bind_group, &.{});
+        pass.setBindGroup(0, app.scene_bind_group, &.{});
         pass.setVertexBuffer(0, app.vertex_buffer, 0, app.vertex_count * @sizeOf(VertexData));
 
-        // Draw the vertices in `vertex_buffer`.
-        pass.draw(app.vertex_count, 1, 0, 0);
+        for (app.model_bind_groups) |model_bind_group| {
+            // Set the model bind group for a specific model we want to render.
+            pass.setBindGroup(1, model_bind_group, &.{});
+            // Draw the vertices in `vertex_buffer`.
+            pass.draw(app.vertex_count, 1, 0, 0);
+        }
     }
 
     // Finish recording commands, creating a `WGPUCommandBuffer`.

src/shader.wgsl

@@ -1,8 +1,17 @@
-@group(0) @binding(0) var<uniform> mvp_matrix: mat4x4<f32>;
+struct SceneUniformBuffer {
+    view_proj_matrix: mat4x4<f32>,
+};
+
+struct ModelUniformBuffer {
+    matrix: mat4x4<f32>,
+    color: vec3<f32>,
+};
+
+@group(0) @binding(0) var<uniform> scene: SceneUniformBuffer;
+@group(1) @binding(0) var<uniform> model: ModelUniformBuffer;
 
 struct VertexInput {
     @location(0) position: vec3<f32>,
-    @location(1) color: vec3<f32>,
 };
 
 struct VertexOutput {
@@ -16,8 +25,9 @@ struct FragmentOutput {
 
 @vertex fn vertex_main(in: VertexInput) -> VertexOutput {
     var out: VertexOutput;
-    out.position = vec4<f32>(in.position, 1.0) * mvp_matrix;
-    out.color    = vec4<f32>(in.color, 1.0);
+    let mvp = model.matrix * scene.view_proj_matrix;
+    out.position = vec4<f32>(in.position, 1.0) * mvp;
+    out.color    = vec4<f32>(model.color, 1.0);
     return out;
 }