Unmultiply colors before brightening

flame-engine · Dec 14, 2024 · 560b0f0 · 560b0f0
1 parent bb734f4
commit 560b0f0
Showing 1 changed file with 31 additions and 11 deletions.
diff --git a/packages/flame/lib/src/extensions/image.dart b/packages/flame/lib/src/extensions/image.dart
@@ -78,17 +78,37 @@ extension ImageExtension on Image {
     final newPixelData = Uint8List(pixelData.length);
 
     for (var i = 0; i < pixelData.length; i += 4) {
-      final color = Color.fromARGB(
-        pixelData[i + 3],
-        pixelData[i + 0],
-        pixelData[i + 1],
-        pixelData[i + 2],
-      ).brighten(amount);
-
-      newPixelData[i] = (color.r * 255).round();
-      newPixelData[i + 1] = (color.g * 255).round();
-      newPixelData[i + 2] = (color.b * 255).round();
-      newPixelData[i + 3] = (color.a * 255).round();
+      final a = pixelData[i + 3] / 255;
+
+      // Lets avoid division by zero.
+      if (a == 0) {
+        newPixelData[i + 0] = pixelData[i + 0];
+        newPixelData[i + 1] = pixelData[i + 1];
+        newPixelData[i + 2] = pixelData[i + 2];
+        newPixelData[i + 3] = pixelData[i + 3];
+        continue;
+      }
+
+      // Unmultiply the color
+      var r = (pixelData[i + 0] / 255) / a;
+      var g = (pixelData[i + 1] / 255) / a;
+      var b = (pixelData[i + 2] / 255) / a;
+
+      // Brighten in a color accurate way
+      r = r + (1.0 - r) * amount;
+      g = g + (1.0 - g) * amount;
+      b = b + (1.0 - b) * amount;
+
+      // Clamp
+      r = r.clamp(0, 1.0);
+      g = g.clamp(0, 1.0);
+      b = b.clamp(0, 1.0);
+
+      // Pre-multiply the new color.
+      newPixelData[i + 0] = (r * a * 255).round();
+      newPixelData[i + 1] = (g * a * 255).round();
+      newPixelData[i + 2] = (b * a * 255).round();
+      newPixelData[i + 3] = pixelData[i + 3];
     }
     return fromPixels(newPixelData, width, height);
   }