Render triangles as 3 separate models

src/main.zig

@@ -6,66 +6,136 @@ const zm = @import("zmath");
 const vec = zm.f32x4;
 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,
+};
+
 pub const App = @This();
 
 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,
 
 pub fn init(app: *App) !void {
     try core.init(.{});
 
+    app.app_timer = try core.Timer.start();
+    app.title_timer = try core.Timer.start();
+
     const shader_module = core.device.createShaderModuleWGSL("shader.wgsl", @embedFile("shader.wgsl"));
     defer shader_module.release();
 
-    const blend = gpu.BlendState{};
-    const color_target = gpu.ColorTargetState{
-        .format = core.descriptor.format,
-        .blend = &blend,
-        .write_mask = gpu.ColorWriteMaskFlags.all,
-    };
-    const fragment = gpu.FragmentState.init(.{
-        .module = shader_module,
-        .entry_point = "frag_main",
-        .targets = &.{color_target},
-    });
-    const pipeline_descriptor = gpu.RenderPipeline.Descriptor{
-        .vertex = gpu.VertexState{
+    // Set up rendering pipeline.
+    app.pipeline = core.device.createRenderPipeline(&.{
+        .vertex = gpu.VertexState.init(.{
             .module = shader_module,
             .entry_point = "vertex_main",
+            .buffers = &.{
+                gpu.VertexBufferLayout.init(.{
+                    .array_stride = @sizeOf(VertexData),
+                    .step_mode = .vertex,
+                    .attributes = &.{
+                        .{ .format = .float32x3, .shader_location = 0, .offset = @offsetOf(VertexData, "position") },
                     },
-        .fragment = &fragment,
-    };
-
-    app.app_timer = try core.Timer.start();
-    app.title_timer = try core.Timer.start();
+                }),
+            },
+        }),
+        .fragment = &gpu.FragmentState.init(.{
+            .module = shader_module,
+            .entry_point = "frag_main",
+            .targets = &.{.{ .format = core.descriptor.format }},
+        }),
+    });
 
-    app.pipeline = core.device.createRenderPipeline(&pipeline_descriptor);
+    // Set up uniform buffers and bind groups.
 
-    app.mvp_uniform_buffer = core.device.createBuffer(&.{
+    // 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.
+    const vertices = [_]VertexData{
+        .{ .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(&.{
+        .size = app.vertex_count * @sizeOf(VertexData),
+        .usage = .{ .vertex = true, .copy_dst = true },
+        .mapped_at_creation = .false,
+    });
+    // Upload vertex buffer to the GPU.
+    core.queue.writeBuffer(app.vertex_buffer, 0, &vertices);
 }
 
 pub fn deinit(app: *App) void {
+    // Using `defer` here, so we can specify them
+    // 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();
 }
 
 pub fn update(app: *App) !bool {
@@ -101,21 +171,25 @@ pub fn update(app: *App) !bool {
     // Once rendering is done (hence `defer`), swap back buffer to the front to display.
     defer core.swap_chain.present();
 
-    const color_attachment = gpu.RenderPassColorAttachment{
+    const render_pass_info = gpu.RenderPassDescriptor.init(.{
+        .color_attachments = &.{.{
             .view = back_buffer_view,
             .clear_value = std.mem.zeroes(gpu.Color),
             .load_op = .clear,
             .store_op = .store,
-    };
-    const render_pass_info = gpu.RenderPassDescriptor.init(.{
-        .color_attachments = &.{color_attachment},
+        }},
     });
 
     // Create a `WGPUCommandEncoder` which provides an interface for recording GPU commands.
     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);
@@ -123,10 +197,15 @@ pub fn update(app: *App) !bool {
         defer pass.end();
 
         pass.setPipeline(app.pipeline);
-        pass.setBindGroup(0, app.mvp_bind_group, &.{});
-
-        // Draw three triangles with the help of a specialized shader.
-        pass.draw(9, 1, 0, 0);
+        pass.setBindGroup(0, app.scene_bind_group, &.{});
+        pass.setVertexBuffer(0, app.vertex_buffer, 0, app.vertex_count * @sizeOf(VertexData));
+
+        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

@@ -1,4 +1,18 @@
-@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>,
+};
 
 struct VertexOutput {
     @builtin(position) position: vec4<f32>,
@@ -9,31 +23,11 @@ struct FragmentOutput {
     @location(0) pixel_color: vec4<f32>
 };
 
-@vertex fn vertex_main(
-    @builtin(vertex_index) index: u32
-) -> VertexOutput {
-    let color = array<vec3<f32>, 3>(
-        vec3<f32>(1.0, 0.0, 0.0),
-        vec3<f32>(0.0, 1.0, 0.0),
-        vec3<f32>(0.0, 0.0, 1.0),
-    );
-    let pos = array<vec2<f32>, 9>(
-        vec2<f32>(-1.0,  0.5 + 0.25),
-        vec2<f32>(-1.5, -0.5 + 0.25),
-        vec2<f32>(-0.5, -0.5 + 0.25),
-
-        vec2<f32>( 0.0,  0.5 - 0.25),
-        vec2<f32>(-0.5, -0.5 - 0.25),
-        vec2<f32>( 0.5, -0.5 - 0.25),
-
-        vec2<f32>( 1.0,  0.5),
-        vec2<f32>( 0.5, -0.5),
-        vec2<f32>( 1.5, -0.5),
-    );
-
+@vertex fn vertex_main(in: VertexInput) -> VertexOutput {
     var out: VertexOutput;
-    out.position = vec4<f32>(pos[index], 0.0, 1.0) * mvp_matrix;
-    out.color    = vec4<f32>(color[index / 3], 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;
 }