From 9f710b0fb6997b6e80c1d3edca40cf8c680fc442 Mon Sep 17 00:00:00 2001
From: MacDue <macdue@dueutil.tech>
Date: Sun, 21 Jan 2024 23:29:01 +0000
Subject: [PATCH] Revert "LibGfx: Slightly simplify Color::blend()"

This was producing incorrect results.

This reverts commit a1bafafd7805f2163c9afe45163cef07c212e9ce.
---
 .../svg-background-no-natural-size-ref.png      | Bin 400 -> 407 bytes
 Userland/Libraries/LibGfx/Color.h               |   9 +++++----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/Tests/LibWeb/Ref/reference/images/svg-background-no-natural-size-ref.png b/Tests/LibWeb/Ref/reference/images/svg-background-no-natural-size-ref.png
index a56a3670244f83f37ea95c022069b12f534260ef..fe5c015a42a824d1828bb87f28612ce257e2d8e0 100644
GIT binary patch
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literal 400
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diff --git a/Userland/Libraries/LibGfx/Color.h b/Userland/Libraries/LibGfx/Color.h
index c9c9f357a9..827b37175f 100644
--- a/Userland/Libraries/LibGfx/Color.h
+++ b/Userland/Libraries/LibGfx/Color.h
@@ -210,10 +210,11 @@ public:
         if (source.alpha() == 0)
             return *this;
 
-        u8 a = 255 - ((255 - alpha()) * (255 - source.alpha()) / 255);
-        u8 r = (red() * (255 - source.alpha()) + source.red() * source.alpha()) / 255;
-        u8 g = (green() * (255 - source.alpha()) + source.green() * source.alpha()) / 255;
-        u8 b = (blue() * (255 - source.alpha()) + source.blue() * source.alpha()) / 255;
+        int const d = 255 * (alpha() + source.alpha()) - alpha() * source.alpha();
+        u8 r = (red() * alpha() * (255 - source.alpha()) + source.red() * 255 * source.alpha()) / d;
+        u8 g = (green() * alpha() * (255 - source.alpha()) + source.green() * 255 * source.alpha()) / d;
+        u8 b = (blue() * alpha() * (255 - source.alpha()) + source.blue() * 255 * source.alpha()) / d;
+        u8 a = d / 255;
         return Color(r, g, b, a);
     }