initialized the draw buffer with the CPU

Cargo.toml

@@ -9,3 +9,4 @@ nalgebra = "0.30.1"
 winit = "0.26"
 wgpu = "0.12"
 pollster = "0.2"
+image = "0.24"

src/render_loop.rs

@@ -1,6 +1,7 @@
 
 use winit::{event_loop::{EventLoop, ControlFlow}, window::WindowBuilder, window::Window, event::{Event, WindowEvent, DeviceEvent}, dpi::{Size, PhysicalSize}};
-use wgpu::{Instance, Surface, Backends, Features, Adapter, DeviceDescriptor, Device, Queue, Texture, TextureDescriptor, TextureDimension, TextureFormat, TextureUsages, Extent3d, CommandEncoder, CommandEncoderDescriptor, CommandBuffer, ImageCopyTexture, Origin3d, TextureAspect, SurfaceConfiguration, SurfaceTexture, PresentMode};
+use wgpu::{Instance, Surface, Backends, Features, Adapter, DeviceDescriptor, Device, Queue, Texture, TextureDescriptor, TextureDimension, TextureFormat, TextureUsages, Extent3d, CommandEncoder, CommandEncoderDescriptor, CommandBuffer, ImageCopyTexture, Origin3d, TextureAspect, SurfaceConfiguration, SurfaceTexture, PresentMode, ImageDataLayout};
+use image::{flat::{FlatSamples, SampleLayout}, ColorType};
 
 const DEFAULT_DIMS: [u32; 2] = [100, 100];
 
@@ -12,6 +13,7 @@ pub struct RenderLoop {
     device: Device,
     queue: Queue,
     texture_buffer: Texture,
+    cpu_image: FlatSamples<Vec<u8>>,
 }
 
 impl RenderLoop {
@@ -78,6 +80,19 @@ impl RenderLoop {
               height: win_size.height,
               present_mode: PresentMode::Mailbox,
           });
+
+      let cpu_image = FlatSamples {
+        samples: vec![64u8; win_size.width as usize * win_size.height as usize * 4],
+        layout: SampleLayout {
+          channels: 4,
+          channel_stride: 1,
+          width: win_size.width,
+          width_stride: 4,
+          height: win_size.height,
+          height_stride: win_size.width as usize * 4,
+        },
+        color_hint: Some(ColorType::Rgba8),
+      };
       Some((event_loop, RenderLoop {
           window,
           instance,
@@ -86,6 +101,7 @@ impl RenderLoop {
           device,
           queue,
           texture_buffer: texture,
+          cpu_image,
           })
           )
     }
@@ -115,6 +131,18 @@ impl RenderLoop {
               height: win_size.height,
               present_mode: PresentMode::Mailbox,
           });
+      self.cpu_image = FlatSamples {
+        samples: vec![64u8; win_size.width as usize * win_size.height as usize * 4],
+        layout: SampleLayout {
+          channels: 4,
+          channel_stride: 1,
+          width: win_size.width,
+          width_stride: 4,
+          height: win_size.height,
+          height_stride: win_size.width as usize * 4,
+        },
+        color_hint: Some(ColorType::Rgba8),
+      };
     }
 
     async fn render(&mut self) -> Option<()>{
@@ -126,8 +154,27 @@ impl RenderLoop {
           self.rebuild().await;
         }
       };
-      let mut encoder = self.device.create_command_encoder(&CommandEncoderDescriptor { label: None });
       let win_size = self.window.inner_size();
+      self.queue.write_texture(
+          ImageCopyTexture {
+              texture: &self.texture_buffer,
+              mip_level: 0,
+              origin: Origin3d::ZERO,
+              aspect: TextureAspect::All,
+          },
+          &self.cpu_image.samples,
+          ImageDataLayout {
+              offset: 0,
+              bytes_per_row: core::num::NonZeroU32::new(win_size.width * 4),
+              rows_per_image: None,
+          },
+          Extent3d {
+              width: win_size.width,
+              height: win_size.height,
+              depth_or_array_layers: 1,
+          }
+      );
+      let mut encoder = self.device.create_command_encoder(&CommandEncoderDescriptor { label: None });
       encoder.copy_texture_to_texture(
           ImageCopyTexture {
               texture: &self.texture_buffer,