Address initial review feedback

* Add comment about naughty ptr2int cast
* Change Option to anyhow::Result in test scene ImageCache
* Replace magic constant with pixel stride from selected format

examples/scenes/src/images.rs

@@ -16,38 +16,36 @@ impl ImageCache {
         Self::default()
     }
 
-    pub fn from_file(&mut self, path: impl AsRef<Path>) -> Option<Image> {
+    pub fn from_file(&mut self, path: impl AsRef<Path>) -> anyhow::Result<Image> {
         let path = path.as_ref();
         if let Some(image) = self.files.get(path) {
-            Some(image.clone())
+            Ok(image.clone())
         } else {
-            let data = std::fs::read(path).ok()?;
+            let data = std::fs::read(path)?;
             let image = decode_image(&data)?;
             self.files.insert(path.to_owned(), image.clone());
-            Some(image)
+            Ok(image)
         }
     }
 
-    pub fn from_bytes(&mut self, key: usize, bytes: &[u8]) -> Option<Image> {
+    pub fn from_bytes(&mut self, key: usize, bytes: &[u8]) -> anyhow::Result<Image> {
         if let Some(image) = self.bytes.get(&key) {
-            Some(image.clone())
+            Ok(image.clone())
         } else {
             let image = decode_image(bytes)?;
             self.bytes.insert(key, image.clone());
-            Some(image)
+            Ok(image)
         }
     }
 }
 
-fn decode_image(data: &[u8]) -> Option<Image> {
+fn decode_image(data: &[u8]) -> anyhow::Result<Image> {
     let image = image::io::Reader::new(std::io::Cursor::new(data))
-        .with_guessed_format()
+        .with_guessed_format()?
-        .ok()?
+        .decode()?;
-        .decode()
-        .ok()?;
     let width = image.width();
     let height = image.height();
     let data = Arc::new(image.into_rgba8().into_vec());
     let blob = Blob::new(data);
-    Some(Image::new(blob, Format::Rgba8, width, height))
+    Ok(Image::new(blob, Format::Rgba8, width, height))
 }

examples/scenes/src/test_scenes.rs

@@ -101,6 +101,8 @@ fn cardioid_and_friends(sb: &mut SceneBuilder, _: &mut SceneParams) {
 }
 
 fn animated_text(sb: &mut SceneBuilder, params: &mut SceneParams) {
+    // Uses the static array address as a cache key for expedience. Real code
+    // should use a better strategy.
     let piet_logo = params
         .images
         .from_bytes(PIET_LOGO_IMAGE.as_ptr() as usize, PIET_LOGO_IMAGE)

src/engine.rs

@@ -299,7 +299,7 @@ impl Engine {
                         base_mip_level: 0,
                         base_array_layer: 0,
                         array_layer_count: None,
-                        format: Some(TextureFormat::Rgba8Unorm),
+                        format: Some(format),
                     });
                     queue.write_texture(
                         wgpu::ImageCopyTexture {
@@ -311,7 +311,9 @@ impl Engine {
                         bytes,
                         wgpu::ImageDataLayout {
                             offset: 0,
-                            bytes_per_row: NonZeroU32::new(image_proxy.width * 4),
+                            bytes_per_row: NonZeroU32::new(
+                                image_proxy.width * format.describe().block_size as u32,
+                            ),
                             rows_per_image: None,
                         },
                         wgpu::Extent3d {
@@ -325,6 +327,7 @@ impl Engine {
                 }
                 Command::WriteImage(proxy, [x, y, width, height], data) => {
                     if let Ok((texture, _)) = self.bind_map.get_or_create_image(*proxy, device) {
+                        let format = proxy.format.to_wgpu();
                         queue.write_texture(
                             wgpu::ImageCopyTexture {
                                 texture: &texture,
@@ -335,7 +338,9 @@ impl Engine {
                             &data[..],
                             wgpu::ImageDataLayout {
                                 offset: 0,
-                                bytes_per_row: NonZeroU32::new(*width * 4),
+                                bytes_per_row: NonZeroU32::new(
+                                    *width * format.describe().block_size as u32,
+                                ),
                                 rows_per_image: None,
                             },
                             wgpu::Extent3d {
@@ -778,7 +783,7 @@ impl BindMap {
                     base_mip_level: 0,
                     base_array_layer: 0,
                     array_layer_count: None,
-                    format: Some(TextureFormat::Rgba8Unorm),
+                    format: Some(proxy.format.to_wgpu()),
                 });
                 Ok(vacant.insert((texture, texture_view)))
             }