From: Tim Toohey <ttoohey@php.net>
Date: Mon, 30 Sep 2002 07:23:34 +0000 (+0000)
Subject: fix gdImageCopyResampled() for non-constant alpha layer
X-Git-Tag: MODERN_SYMMETRIC_SESSION_BEHAVIOUR_20021003~67
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=6a952f0856d6688139d944df034c3f0c586c23dc;p=php

fix gdImageCopyResampled() for non-constant alpha layer
---

diff --git a/ext/gd/libgd/gd.c b/ext/gd/libgd/gd.c
index 5a439e7a03..ff6d4425cf 100644
--- a/ext/gd/libgd/gd.c
+++ b/ext/gd/libgd/gd.c
@@ -2047,6 +2047,7 @@ gdImageCopyResampled (gdImagePtr dst,
 	  float sx, sy;
 	  float spixels = 0.0f;
 	  float red = 0.0f, green = 0.0f, blue = 0.0f, alpha = 0.0f;
+	  float alpha_factor, alpha_sum = 0.0f, contrib_sum = 0.0f;
 	  sy1 = ((float)(y - dstY)) * (float)srcH /
 	    (float)dstH;
 	  sy2 = ((float)(y + 1 - dstY)) * (float) srcH /
@@ -2104,10 +2105,13 @@ gdImageCopyResampled (gdImagePtr dst,
 						 src,
 						 (int) sx + srcX,
 						 (int) sy + srcY);
-		  red += gdTrueColorGetRed (p) * pcontribution;
-		  green += gdTrueColorGetGreen (p) * pcontribution;
-		  blue += gdTrueColorGetBlue (p) * pcontribution;
+		  alpha_factor = ((gdAlphaMax - gdTrueColorGetAlpha(p))) * pcontribution;
+		  red += gdTrueColorGetRed (p) * alpha_factor;
+		  green += gdTrueColorGetGreen (p) * alpha_factor;
+		  blue += gdTrueColorGetBlue (p) * alpha_factor;
 		  alpha += gdTrueColorGetAlpha (p) * pcontribution;
+		  alpha_sum += alpha_factor;
+		  contrib_sum += pcontribution;
 		  spixels += xportion * yportion;
 		  sx += 1.0f;
 		}
@@ -2122,6 +2126,13 @@ gdImageCopyResampled (gdImagePtr dst,
 	      blue /= spixels;
 	      alpha /= spixels;
 	    }
+          if ( alpha_sum != 0.0f)
+            {
+              if( contrib_sum != 0.0f ) alpha_sum /= contrib_sum;
+              red /= alpha_sum;
+              green /= alpha_sum;
+              blue /= alpha_sum;
+            }
 	  /* Clamping to allow for rounding errors above */
 	  if (red > 255.0f)
 	    {