Add minimal infrastructure for overriding an Image (#636)

This is related to linebender/xilem#395

See also [#gpu > vello adding wgpu texture buffers to
scene](https://xi.zulipchat.com/#narrow/stream/197075-gpu/topic/vello.20adding.20wgpu.20texture.20buffers.20to.20scene)

This is a targeted hack working within our current API.

vello/src/lib.rs

@@ -89,7 +89,7 @@ mod shaders;
 mod wgpu_engine;
 
 #[cfg(feature = "wgpu")]
-use std::num::NonZeroUsize;
+use std::{num::NonZeroUsize, sync::Arc};
 
 /// Styling and composition primitives.
 pub use peniko;
@@ -329,6 +329,20 @@ impl Renderer {
  })
  }
 
+ /// Overwrite the `Image` with the `Texture` texture.
+ ///
+ /// If texture is `None`, removes the override.
+ pub fn override_image(
+ &mut self,
+ image: &peniko::Image,
+ texture: Option<Arc<wgpu::ImageCopyTextureBase<wgpu::Texture>>>,
+ ) -> Option<Arc<wgpu::ImageCopyTextureBase<wgpu::Texture>>> {
+ match texture {
+ Some(texture) => self.engine.image_overrides.insert(image.data.id(), texture),
+ None => self.engine.image_overrides.remove(&image.data.id()),
+ }
+ }
+
  /// Renders a scene to the target texture.
  ///
  /// The texture is assumed to be of the specified dimensions and have been created with

vello/src/recording.rs

@@ -4,6 +4,8 @@
 use std::num::NonZeroU64;
 use std::sync::atomic::{AtomicU64, Ordering};
 
+use peniko::Image;
+
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Default)]
 pub struct ShaderId(pub usize);
 
@@ -61,7 +63,7 @@ pub enum Command {
  UploadUniform(BufferProxy, Vec<u8>),
  /// Commands the data to be uploaded to the given image.
  UploadImage(ImageProxy, Vec<u8>),
- WriteImage(ImageProxy, [u32; 4], Vec<u8>),
+ WriteImage(ImageProxy, [u32; 2], Image),
  // Discussion question: third argument is vec of resources?
  // Maybe use tricks to make more ergonomic?
  // Alternative: provide bufs & images as separate sequences
@@ -133,17 +135,8 @@ impl Recording {
  image_proxy
  }
 
- pub fn write_image(
- &mut self,
- image: ImageProxy,
- x: u32,
- y: u32,
- width: u32,
- height: u32,
- data: impl Into<Vec<u8>>,
- ) {
- let data = data.into();
- self.push(Command::WriteImage(image, [x, y, width, height], data));
+ pub fn write_image(&mut self, proxy: ImageProxy, x: u32, y: u32, image: Image) {
+ self.push(Command::WriteImage(proxy, [x, y], image));
  }
 
  pub fn dispatch<R>(&mut self, shader: ShaderId, wg_size: (u32, u32, u32), resources: R)

vello/src/render.rs

@@ -113,14 +113,7 @@ impl Render {
  ImageProxy::new(images.width, images.height, ImageFormat::Rgba8)
  };
  for image in images.images {
- recording.write_image(
- image_atlas,
- image.1,
- image.2,
- image.0.width,
- image.0.height,
- image.0.data.data(),
- );
+ recording.write_image(image_atlas, image.1, image.2, image.0.clone());
  }
  let cpu_config =
  RenderConfig::new(&layout, params.width, params.height, &params.base_color);

vello/src/wgpu_engine.rs

@@ -5,6 +5,7 @@ use std::borrow::Cow;
 use std::cell::RefCell;
 use std::collections::hash_map::Entry;
 use std::collections::{HashMap, HashSet};
+use std::sync::Arc;
 
 use vello_shaders::cpu::CpuBinding;
 
@@ -36,6 +37,10 @@ pub struct WgpuEngine {
  #[cfg(not(target_arch = "wasm32"))]
  shaders_to_initialise: Option<Vec<UninitialisedShader>>,
  pub(crate) use_cpu: bool,
+ /// Overrides from a specific `Image`'s [`id`](peniko::Image::id) to a wgpu `Texture`.
+ ///
+ /// The `Texture` should have the same size as the `Image`.
+ pub(crate) image_overrides: HashMap<u64, Arc<wgpu::ImageCopyTextureBase<Texture>>>,
 }
 
 struct WgpuShader {
@@ -433,31 +438,53 @@ impl WgpuEngine {
  self.bind_map
  .insert_image(image_proxy.id, texture, texture_view);
  }
- Command::WriteImage(proxy, [x, y, width, height], data) => {
+ Command::WriteImage(proxy, [x, y], image) => {
  let (texture, _) = self.bind_map.get_or_create_image(*proxy, device);
  let format = proxy.format.to_wgpu();
  let block_size = format
  .block_copy_size(None)
  .expect("ImageFormat must have a valid block size");
- queue.write_texture(
- wgpu::ImageCopyTexture {
- texture,
- mip_level: 0,
- origin: wgpu::Origin3d { x: *x, y: *y, z: 0 },
- aspect: TextureAspect::All,
- },
- &data[..],
- wgpu::ImageDataLayout {
- offset: 0,
- bytes_per_row: Some(*width * block_size),
- rows_per_image: None,
- },
- wgpu::Extent3d {
- width: *width,
- height: *height,
- depth_or_array_layers: 1,
- },
- );
+ if let Some(overrider) = self.image_overrides.get(&image.data.id()) {
+ encoder.copy_texture_to_texture(
+ wgpu::ImageCopyTexture {
+ texture: &overrider.texture,
+ mip_level: overrider.mip_level,
+ origin: overrider.origin,
+ aspect: overrider.aspect,
+ },
+ wgpu::ImageCopyTexture {
+ texture,
+ mip_level: 0,
+ origin: wgpu::Origin3d { x: *x, y: *y, z: 0 },
+ aspect: TextureAspect::All,
+ },
+ wgpu::Extent3d {
+ width: image.width,
+ height: image.height,
+ depth_or_array_layers: 1,
+ },
+ );
+ } else {
+ queue.write_texture(
+ wgpu::ImageCopyTexture {
+ texture,
+ mip_level: 0,
+ origin: wgpu::Origin3d { x: *x, y: *y, z: 0 },
+ aspect: TextureAspect::All,
+ },
+ image.data.data(),
+ wgpu::ImageDataLayout {
+ offset: 0,
+ bytes_per_row: Some(image.width * block_size),
+ rows_per_image: None,
+ },
+ wgpu::Extent3d {
+ width: image.width,
+ height: image.height,
+ depth_or_array_layers: 1,
+ },
+ );
+ }
  }
  Command::Dispatch(shader_id, wg_size, bindings) => {
  // println!("dispatching {:?} with {} bindings", wg_size, bindings.len());