Actually run the compute pass, show offset issues

blog/2025-03-30-draw-compute-shader/draw-compute/shader/src/lib.rs

@@ -6,12 +6,12 @@ use spirv_std::spirv;
 #[derive(Copy, Clone, bytemuck::Pod, bytemuck::Zeroable)]
 #[repr(C)]
 pub struct Viewport {
-    pub image_size: glam::UVec2,
+    pub offset: glam::UVec2,
-    pub viewport_offset: glam::UVec2,
+    pub size: glam::UVec2,
-    pub viewport_size: glam::UVec2,
+    pub image: glam::UVec2,
 }
 
-const BLOCK_SIZE: u32 = 16;
+const BLOCK_SIZE: usize = 16;
 const BLACK: glam::Vec4 = glam::vec4(0.0, 0.0, 0.0, 1.0);
 const WHITE: glam::Vec4 = glam::vec4(1.0, 1.0, 1.0, 1.0);
 
@@ -24,18 +24,16 @@ pub fn main_cs(
     #[spirv(uniform, descriptor_set = 0, binding = 0)] viewport: &Viewport,
     #[spirv(storage_buffer, descriptor_set = 0, binding = 1)] image: &mut [glam::Vec4],
 ) {
-    let width = viewport.image_size.x as usize;
+    let width = viewport.image.x as usize;
-    let height = viewport.image_size.y as usize;
+    let height = viewport.image.y as usize;
     for x in 0..width {
+        let x_even = x / BLOCK_SIZE % 2 == 0;
         for y in 0..height {
+            let y_even = y / BLOCK_SIZE % 2 == 0;
+
+            let color = if x_even == y_even { BLACK } else { WHITE };
             let index = image_index(x, y, width);
-            if x == 0
+            image[index] = color;
-                || x == width - 1
-                || y == 0
-                || y == height - 1
-            {
-                image[index] = WHITE;
-            }
         }
     }
 }
@@ -58,10 +56,9 @@ pub fn main_fs(
 ) {
     let pixel_coordinate = frag_coord.xy().as_usizevec2();
     let (pixel_x, pixel_y) = (pixel_coordinate.x, pixel_coordinate.y);
-    let index = image_index(pixel_x, pixel_y, viewport.viewport_size.x as usize);
 
-    *output = if index < image.len() {
+    *output = if pixel_x < viewport.image.x as usize && pixel_y < viewport.image.y as usize {
-        image[index]
+        image[image_index(pixel_x, pixel_y, viewport.image.x as usize)]
     } else {
         BLACK
     };

blog/2025-03-30-draw-compute-shader/draw-compute/src/main.rs

@@ -3,7 +3,6 @@ use eframe::wgpu::{CommandBuffer, CommandEncoder, Device, Queue, RenderPass};
 use eframe::Frame;
 use egui::{Context, Sense};
 use egui_wgpu::{CallbackResources, CallbackTrait, ScreenDescriptor};
-use shader::Viewport;
 
 struct DrawResources {
     device: wgpu::Device,
@@ -11,7 +10,7 @@ struct DrawResources {
     bind_group: wgpu::BindGroup,
     viewport_buffer: wgpu::Buffer,
     image_buffer: wgpu::Buffer,
-    image_buffer_size: glam::UVec2,
+    image_size: glam::UVec2,
     compute_pipeline: wgpu::ComputePipeline,
     render_pipeline: wgpu::RenderPipeline,
 }
@@ -150,7 +149,7 @@ impl DrawResources {
         let bind_group_layout = Self::bind_group_layout(device);
         let viewport_buffer = Self::viewport_buffer(device);
         let image_buffer = Self::image_buffer(device, width, height);
-        let image_buffer_size = glam::uvec2(width as u32, height as u32);
+        let image_size = glam::uvec2(width as u32, height as u32);
 
         let bind_group =
             Self::bind_group(device, &bind_group_layout, &viewport_buffer, &image_buffer);
@@ -165,7 +164,7 @@ impl DrawResources {
             bind_group,
             viewport_buffer,
             image_buffer,
-            image_buffer_size,
+            image_size,
             compute_pipeline,
             render_pipeline,
         }
@@ -196,28 +195,33 @@ impl CallbackTrait for DrawCallback {
         egui_encoder: &mut CommandEncoder,
         callback_resources: &mut CallbackResources,
     ) -> Vec<CommandBuffer> {
-
         let resources = callback_resources
             .get_mut::<DrawResources>()
             .expect("missing draw resources");
 
-        let mut viewport = Viewport {
+        if self.draw_resize {
-            image_size: resources.image_buffer_size,
+            resources.resize(
-            viewport_offset: glam::uvec2(self.draw_rect.min.x as u32, self.draw_rect.min.y as u32),
+                self.draw_rect.size().x as u64,
-            viewport_size: glam::uvec2(self.draw_rect.size().x as u32, self.draw_rect.size().y as u32),
+                self.draw_rect.size().y as u64,
-        };
+            );
-
-        if !self.draw_resize {
-            queue.write_buffer(&resources.viewport_buffer, 0, bytemuck::cast_slice(&[viewport]));
-            return vec![];
         }
 
-        let draw_size = self.draw_rect.size();
+        let mut viewport = shader::Viewport {
-        resources.resize(draw_size.x as u64, draw_size.y as u64);
+            image: resources.image_size,
+            offset: glam::uvec2(self.draw_rect.min.x as u32, self.draw_rect.min.y as u32),
+            size: glam::uvec2(
+                self.draw_rect.size().x as u32,
+                self.draw_rect.size().y as u32,
+            ),
+        };
 
-        viewport.image_size = resources.image_buffer_size;
+        queue.write_buffer(
-        queue.write_buffer(&resources.viewport_buffer, 0, bytemuck::cast_slice(&[viewport]));
+            &resources.viewport_buffer,
+            0,
+            bytemuck::cast_slice(&[viewport]),
+        );
 
+        if self.draw_resize {
             let mut compute_pass = egui_encoder.begin_compute_pass(&wgpu::ComputePassDescriptor {
                 label: Some("compute"),
                 timestamp_writes: None,
@@ -225,6 +229,8 @@ impl CallbackTrait for DrawCallback {
 
             compute_pass.set_pipeline(&resources.compute_pipeline);
             compute_pass.set_bind_group(0, &resources.bind_group, &[]);
+            compute_pass.dispatch_workgroups(1, 1, 1);
+        }
 
         vec![]
     }