1 files changed, 56 insertions, 0 deletions
diff --git a/gfx/wr/wrench/src/premultiply.rs b/gfx/wr/wrench/src/premultiply.rs
new file mode 100644
index 0000000000..04f43add56
--- /dev/null
+++ b/gfx/wr/wrench/src/premultiply.rs
@@ -0,0 +1,56 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// These are slow. Gecko's gfx/2d/Swizzle.cpp has better versions
+pub fn premultiply(data: &mut [u8]) {
+    for pixel in data.chunks_mut(4) {
+        let a = pixel[3] as u32;
+        let b = pixel[2] as u32;
+        let g = pixel[1] as u32;
+        let r = pixel[0] as u32;
+
+        pixel[3] = a as u8;
+        pixel[2] = ((r * a + 128) / 255) as u8;
+        pixel[1] = ((g * a + 128) / 255) as u8;
+        pixel[0] = ((b * a + 128) / 255) as u8;
+    }
+}
+
+#[allow(unused)]
+pub fn unpremultiply(data: &mut [u8]) {
+    for pixel in data.chunks_mut(4) {
+        let a = pixel[3] as u32;
+        let mut b = pixel[2] as u32;
+        let mut g = pixel[1] as u32;
+        let mut r = pixel[0] as u32;
+
+        if a > 0 {
+            r = r * 255 / a;
+            g = g * 255 / a;
+            b = b * 255 / a;
+        }
+
+        pixel[3] = a as u8;
+        pixel[2] = r as u8;
+        pixel[1] = g as u8;
+        pixel[0] = b as u8;
+    }
+}
+
+#[test]
+fn it_works() {
+    let mut f = [0xff, 0xff, 0xff, 0x80, 0x00, 0xff, 0x00, 0x80];
+    premultiply(&mut f);
+    println!("{:?}", f);
+    assert!(
+        f[0] == 0x80 && f[1] == 0x80 && f[2] == 0x80 && f[3] == 0x80 && f[4] == 0x00 &&
+            f[5] == 0x80 && f[6] == 0x00 && f[7] == 0x80
+    );
+    unpremultiply(&mut f);
+    println!("{:?}", f);
+    assert!(
+        f[0] == 0xff && f[1] == 0xff && f[2] == 0xff && f[3] == 0x80 && f[4] == 0x00 &&
+            f[5] == 0xff && f[6] == 0x00 && f[7] == 0x80
+    );
+}