Load and convert RGB8 dds textures (#12952)

# Objective

- Closes #12944.

## Solution

- Load `R8G8B8` textures by transcoding to an rgba format since `wgpu`
does not support texture formats with 3 channels.
- Switch to erroring out instead of panicking on an invalid dds file.

---

## Changelog

### Added

- DDS Textures with the `R8G8B8` format are now supported. They require
an additional conversion step, so using `R8G8B8A8` or a similar format
is preferable for texture loading performance.

crates/bevy_image/src/dds.rs

@@ -8,7 +8,7 @@ use wgpu_types::{
 #[cfg(debug_assertions)]
 use {bevy_utils::once, tracing::warn};
 
-use super::{CompressedImageFormats, Image, TextureError};
+use super::{CompressedImageFormats, Image, TextureError, TranscodeFormat};
 
 #[cfg(feature = "dds")]
 pub fn dds_buffer_to_image(
@@ -20,7 +20,18 @@ pub fn dds_buffer_to_image(
     let mut cursor = Cursor::new(buffer);
     let dds = Dds::read(&mut cursor)
         .map_err(|error| TextureError::InvalidData(format!("Failed to parse DDS file: {error}")))?;
-    let texture_format = dds_format_to_texture_format(&dds, is_srgb)?;
+    let (texture_format, transcode_format) = match dds_format_to_texture_format(&dds, is_srgb) {
+        Ok(format) => (format, None),
+        Err(TextureError::FormatRequiresTranscodingError(TranscodeFormat::Rgb8)) => {
+            let format = if is_srgb {
+                TextureFormat::Bgra8UnormSrgb
+            } else {
+                TextureFormat::Bgra8Unorm
+            };
+            (format, Some(TranscodeFormat::Rgb8))
+        }
+        Err(error) => return Err(error),
+    };
     if !supported_compressed_formats.supports(texture_format) {
         return Err(TextureError::UnsupportedTextureFormat(format!(
             "Format not supported by this GPU: {texture_format:?}",
@@ -86,7 +97,29 @@ pub fn dds_buffer_to_image(
             ..Default::default()
         });
     }
-    image.data = Some(dds.data);
+
+    // DDS mipmap layout is directly compatible with wgpu's layout (Slice -> Face -> Mip):
+    // https://learn.microsoft.com/fr-fr/windows/win32/direct3ddds/dx-graphics-dds-reference
+    image.data = if let Some(transcode_format) = transcode_format {
+        match transcode_format {
+            TranscodeFormat::Rgb8 => {
+                let data = dds
+                    .data
+                    .chunks_exact(3)
+                    .flat_map(|pixel| [pixel[0], pixel[1], pixel[2], u8::MAX])
+                    .collect();
+                Some(data)
+            }
+            _ => {
+                return Err(TextureError::TranscodeError(format!(
+                    "unsupported transcode from {transcode_format:?} to {texture_format:?}"
+                )))
+            }
+        }
+    } else {
+        Some(dds.data)
+    };
+
     Ok(image)
 }
 
@@ -112,6 +145,9 @@ pub fn dds_format_to_texture_format(
                     TextureFormat::Bgra8Unorm
                 }
             }
+            D3DFormat::R8G8B8 => {
+                return Err(TextureError::FormatRequiresTranscodingError(TranscodeFormat::Rgb8));
+            },
             D3DFormat::G16R16 => TextureFormat::Rg16Uint,
             D3DFormat::A2B10G10R10 => TextureFormat::Rgb10a2Unorm,
             D3DFormat::A8L8 => TextureFormat::Rg8Uint,
@@ -153,7 +189,6 @@ pub fn dds_format_to_texture_format(
             // FIXME: Map to argb format and user has to know to ignore the alpha channel?
             | D3DFormat::X8B8G8R8
             | D3DFormat::A2R10G10B10
-            | D3DFormat::R8G8B8
             | D3DFormat::X1R5G5B5
             | D3DFormat::A4R4G4B4
             | D3DFormat::X4R4G4B4

crates/bevy_image/src/image.rs

@@ -1491,19 +1491,20 @@ pub enum DataFormat {
     Rg,
 }
 
+/// Texture data need to be transcoded from this format for use with `wgpu`.
 #[derive(Clone, Copy, Debug)]
 pub enum TranscodeFormat {
     Etc1s,
     Uastc(DataFormat),
-    // Has to be transcoded to R8Unorm for use with `wgpu`
+    // Has to be transcoded to R8Unorm for use with `wgpu`.
     R8UnormSrgb,
-    // Has to be transcoded to R8G8Unorm for use with `wgpu`
+    // Has to be transcoded to R8G8Unorm for use with `wgpu`.
     Rg8UnormSrgb,
-    // Has to be transcoded to Rgba8 for use with `wgpu`
+    // Has to be transcoded to Rgba8 for use with `wgpu`.
     Rgb8,
 }
 
-/// An error that occurs when accessing specific pixels in a texture
+/// An error that occurs when accessing specific pixels in a texture.
 #[derive(Error, Debug)]
 pub enum TextureAccessError {
     #[error("out of bounds (x: {x}, y: {y}, z: {z})")]
@@ -1514,25 +1515,34 @@ pub enum TextureAccessError {
     WrongDimension,
 }
 
-/// An error that occurs when loading a texture
+/// An error that occurs when loading a texture.
 #[derive(Error, Debug)]
 pub enum TextureError {
+    /// Image MIME type is invalid.
     #[error("invalid image mime type: {0}")]
     InvalidImageMimeType(String),
+    /// Image extension is invalid.
     #[error("invalid image extension: {0}")]
     InvalidImageExtension(String),
+    /// Failed to load an image.
     #[error("failed to load an image: {0}")]
     ImageError(#[from] image::ImageError),
+    /// Texture format isn't supported.
     #[error("unsupported texture format: {0}")]
     UnsupportedTextureFormat(String),
+    /// Supercompression isn't supported.
     #[error("supercompression not supported: {0}")]
     SuperCompressionNotSupported(String),
-    #[error("failed to load an image: {0}")]
+    /// Failed to decompress an image.
+    #[error("failed to decompress an image: {0}")]
     SuperDecompressionError(String),
+    /// Invalid data.
     #[error("invalid data: {0}")]
     InvalidData(String),
+    /// Transcode error.
     #[error("transcode error: {0}")]
     TranscodeError(String),
+    /// Format requires transcoding.
     #[error("format requires transcoding: {0:?}")]
     FormatRequiresTranscodingError(TranscodeFormat),
     /// Only cubemaps with six faces are supported.