[librsvg: 1/5] GdkPixbufRGBA, ToGdkPixbufRGBA - start naming types and conversion traits for pixel formats

[Marge Bot <marge-bot src gnome org>]

commit 5c05ded662785c6802ae322234fc48128dc90951
Author: Federico Mena Quintero <federico gnome org>
Date:   Tue Sep 21 12:05:27 2021 -0500

    GdkPixbufRGBA, ToGdkPixbufRGBA - start naming types and conversion traits for pixel formats
    
    The code assumes that struct Pixel is always the layout that GdkPixbuf
    uses.  This is true right now, but is a hidden assumption.  Let's
    start giving better names to pixel formats.
    
    Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/592>

 src/surface_utils/mod.rs            | 23 +++++++++++++++++++++++
 src/surface_utils/shared_surface.rs |  4 ++--
 2 files changed, 25 insertions(+), 2 deletions(-)
---
diff --git a/src/surface_utils/mod.rs b/src/surface_utils/mod.rs
index 53bbd00b..93d3b4f7 100644
--- a/src/surface_utils/mod.rs
+++ b/src/surface_utils/mod.rs
@@ -22,6 +22,9 @@ use rgb::alt::ARGB8;
 #[allow(clippy::upper_case_acronyms)]
 pub type CairoARGB = ARGB8;
 
+/// GdkPixbuf's endian-independent RGBA8 pixel layout.
+pub type GdkPixbufRGBA = rgb::RGBA8;
+
 /// Analogous to `rgb::FromSlice`, to convert from `[T]` to `[CairoARGB]`
 #[allow(clippy::upper_case_acronyms)]
 pub trait AsCairoARGB<T: Copy> {
@@ -57,6 +60,26 @@ pub enum EdgeMode {
     None,
 }
 
+/// Trait to convert pixels in various formats to RGBA, for GdkPixbuf.
+///
+/// GdkPixbuf unconditionally uses RGBA ordering regardless of endianness,
+/// but we need to convert to it from Cairo's endian-dependent 0xaarrggbb.
+pub trait ToGdkPixbufRGBA {
+    fn to_pixbuf_rgba(&self) -> GdkPixbufRGBA;
+}
+
+impl ToGdkPixbufRGBA for Pixel {
+    #[inline]
+    fn to_pixbuf_rgba(&self) -> GdkPixbufRGBA {
+        GdkPixbufRGBA {
+            r: self.r,
+            g: self.g,
+            b: self.b,
+            a: self.a,
+        }
+    }
+}
+
 /// Extension methods for `cairo::ImageSurfaceData`.
 pub trait ImageSurfaceDataExt: DerefMut<Target = [u8]> {
     /// Sets the pixel at the given coordinates. Assumes the `ARgb32` format.
diff --git a/src/surface_utils/shared_surface.rs b/src/surface_utils/shared_surface.rs
index 9d328923..476a6f77 100644
--- a/src/surface_utils/shared_surface.rs
+++ b/src/surface_utils/shared_surface.rs
@@ -15,7 +15,7 @@ use crate::util::clamp;
 
 use super::{
     iterators::{PixelRectangle, Pixels},
-    AsCairoARGB, CairoARGB, EdgeMode, ImageSurfaceDataExt, Pixel, PixelOps,
+    AsCairoARGB, CairoARGB, EdgeMode, ImageSurfaceDataExt, Pixel, PixelOps, ToGdkPixbufRGBA,
 };
 
 /// Types of pixel data in a `ImageSurface`.
@@ -342,7 +342,7 @@ impl ImageSurface<Shared> {
             .map(|row| row.as_rgba_mut())
             .zip(self.rows())
             .flat_map(|(dest_row, src_row)| src_row.iter().zip(dest_row.iter_mut()))
-            .for_each(|(src, dest)| *dest = Pixel::from(*src).unpremultiply());
+            .for_each(|(src, dest)| *dest = Pixel::from(*src).unpremultiply().to_pixbuf_rgba());
 
         Some(pixbuf)
     }