Fix #72913: imagecopy() loses single-color transparency on palette images

The proper code to handle true-color to palette copies is already contained
in gdImageCopy(), so we can simply remove the buggy duplicated code.

Author: cmb69

NEWS

@@ -16,6 +16,8 @@ PHP                                                                        NEWS
 - GD:
   . Fixed bug #66005 (imagecopy does not support 1bit transparency on truecolor
     images). (cmb)
+  . Fixed bug #72913 (imagecopy() loses single-color transparency on palette
+    images). (cmb)
 
 - JSON:
   . Fixed bug #72787 (json_decode reads out of bounds). (Jakub Zelenka)

ext/gd/libgd/gd.c

@@ -2266,26 +2266,6 @@ void gdImageCopy (gdImagePtr dst, gdImagePtr src, int dstX, int dstY, int srcX,
 		return;
 	}
 
-	/* Destination is palette based */
-	if (src->trueColor) { /* But source is truecolor (Ouch!) */
-		toy = dstY;
-		for (y = srcY; (y < (srcY + h)); y++) {
-			tox = dstX;
-			for (x = srcX; x < (srcX + w); x++) {
-				int nc;
-				c = gdImageGetPixel (src, x, y);
-
-				/* Get best match possible. */
-				nc = gdImageColorResolveAlpha(dst, gdTrueColorGetRed(c), gdTrueColorGetGreen(c), gdTrueColorGetBlue(c), gdTrueColorGetAlpha(c));
-
-				gdImageSetPixel(dst, tox, toy, nc);
-				tox++;
-			}
-			toy++;
-		}
-		return;
-	}
-
 	/* Palette based to palette based */
 	for (i = 0; i < gdMaxColors; i++) {
 		colorMap[i] = (-1);

ext/gd/tests/bug72913.phpt

@@ -0,0 +1,29 @@
+--TEST--
+Bug #72913 (imagecopy() loses single-color transparency on palette images)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+$base64 = 'iVBORw0KGgoAAAANSUhEUgAAADIAAAAyCAIAAACRXR/mAAAABnRSTlMAAAAAAABu'
+    . 'pgeRAAAAVklEQVRYw+3UQQqAMBAEwf3/p9eTBxEPiWAmWMU8oGFJqgAAuOpzWTX3'
+    . 'xQUti+uRJTZ9V5aY1bOTFZLV7yZr9zt6ibv/qPXfrMpsGipbIy7oqQ8AYJED1plD'
+    . 'y5PCu2sAAAAASUVORK5CYII=';
+$src = imagecreatefromstring(base64_decode($base64));
+
+$dst = imagecreate(50, 50);
+$transparent = imagecolorallocatealpha($dst, 255, 255, 255, 127);
+imagealphablending($dst, false);
+imagesavealpha($dst, true);
+
+imagecopy($dst, $src, 0,0, 0,0, 50,50);
+
+ob_start();
+imagegd($dst);
+echo md5(ob_get_clean()), PHP_EOL;
+?>
+==DONE==
+--EXPECT--
+f03c27f20710e21debd7090c660f1a1e
+==DONE==