Paste P296

Masterwork From Distant Lands
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Authored by dkazakov on Thu, Jan 31, 6:19 PM.
diff --git a/libs/pigment/compositeops/KoCompositeOpAlphaDarken.h b/libs/pigment/compositeops/KoCompositeOpAlphaDarken.h
index e51e1a6..c05668e 100644
--- a/libs/pigment/compositeops/KoCompositeOpAlphaDarken.h
+++ b/libs/pigment/compositeops/KoCompositeOpAlphaDarken.h
@@ -91,7 +91,24 @@ public:
channels_type fullFlowAlpha;
channels_type averageOpacity = scale<channels_type>(*params.lastOpacity);
+ /**
+ * Here we calculate fullFlowAlpha, which shuold strive either to
+ * averageOpacity or opacity (whichever is the greater) or just keep old dstAlpha
+ * value, if both opacity values are not bit enough
+ */
if (averageOpacity > opacity) {
+ /**
+ * This crypty code is basically an optimized version of the folowing:
+ * fullFlowAlpha = averageOpacity *
+ * unionShapeOpacity(srcAlpha / averageOpacity,
+ * dstAlpha / averageOpacity);
+ *
+ * The main idea is: fullFlowAlpha should be as near to averageOpacity as
+ * maximum of srcAlpha and dstAlpha and a bit more. So that in consequent
+ * applications of the blending operation alpha channel would aim to
+ * averageOpacity.
+ */
+
channels_type reverseBlend = KoColorSpaceMaths<channels_type>::divide(dstAlpha, averageOpacity);
fullFlowAlpha = averageOpacity > dstAlpha ? lerp(srcAlpha, averageOpacity, reverseBlend) : dstAlpha;
} else {
@@ -103,8 +120,6 @@ public:
} else {
channels_type zeroFlowAlpha = dstAlpha;
dstAlpha = lerp(zeroFlowAlpha, fullFlowAlpha, flow);
-
-
}
dst[alpha_pos] = dstAlpha;
dkazakov edited the content of this paste. (Show Details)Thu, Jan 31, 6:19 PM
dkazakov changed the title of this paste from untitled to Masterwork From Distant Lands.