Bug 1630481 - make Wrench force external BGRA8 images to known format to avoid needing swizzles. r=kvark

Differential Revision: https://phabricator.services.mozilla.com/D71134

gfx/wr/wrench/reftests/image/texture-rect-ref.yaml

@@ -3,10 +3,10 @@ root:
   items:
     - type: rect
       bounds: [0, 0, 50, 50]
-      color: blue
+      color: red
     - type: rect
       bounds: [50, 0, 50, 50]
-      color: red
+      color: blue
     - type: rect
       bounds: [0, 50, 50, 50]
       color: green

gfx/wr/wrench/src/yaml_frame_reader.rs

@@ -111,7 +111,16 @@ impl LocalExternalImageHandler {
             ImageData::Raw(ref data) => {
                 let gl = device.gl();
                 let texture_ids = gl.gen_textures(1);
-                let format_desc = device.gl_describe_format(desc.format);
+                let format_desc = if desc.format == ImageFormat::BGRA8 {
+                    // Force BGRA8 data to RGBA8 layout to avoid potential
+                    // need for usage of texture-swizzle.
+                    webrender::FormatDesc {
+                        external: gl::BGRA,
+                        .. device.gl_describe_format(ImageFormat::RGBA8)
+                    }
+                } else {
+                    device.gl_describe_format(desc.format)
+                };
 
                 LocalExternalImageHandler::init_gl_texture(
                     texture_ids[0],