Fix #79676: imagescale adds black border with IMG_BICUBIC

We have to loop over all image pixels to avoid the black border.  This
is also done in external libgd in `_gdScaleOneAxis` and `_gdScalePass`.

Author: cmb69

NEWS

@@ -11,6 +11,9 @@ PHP                                                                        NEWS
 - Filter:
   . Fixed bug #73527 (Invalid memory access in php_filter_strip). (cmb)
 
+- GD:
+  . Fixed bug #79676 (imagescale adds black border with IMG_BICUBIC). (cmb)
+
 - OpenSSL:
   . Fixed bug #62890 (default_socket_timeout=-1 causes connection to timeout).
     (cmb)

ext/gd/libgd/gd_interpolation.c

@@ -931,7 +931,7 @@ static inline void _gdScaleRow(gdImagePtr pSrc,  unsigned int src_width, gdImage
     int *p_dst_row = dst->tpixels[row];
 	unsigned int x;
 
-    for (x = 0; x < dst_width - 1; x++) {
+    for (x = 0; x < dst_width; x++) {
 		register unsigned char r = 0, g = 0, b = 0, a = 0;
         const int left = contrib->ContribRow[x].Left;
         const int right = contrib->ContribRow[x].Right;
@@ -967,7 +967,7 @@ static inline int _gdScaleHoriz(gdImagePtr pSrc, unsigned int src_width, unsigne
 		return 0;
 	}
 	/* Scale each row */
-	for (u = 0; u < dst_height - 1; u++) {
+	for (u = 0; u < dst_height; u++) {
 		_gdScaleRow(pSrc, src_width, pDst, dst_width, u, contrib);
 	}
 	_gdContributionsFree (contrib);
@@ -977,7 +977,7 @@ static inline int _gdScaleHoriz(gdImagePtr pSrc, unsigned int src_width, unsigne
 static inline void _gdScaleCol (gdImagePtr pSrc,  unsigned int src_width, gdImagePtr pRes, unsigned int dst_width, unsigned int dst_height, unsigned int uCol, LineContribType *contrib)
 {
 	unsigned int y;
-	for (y = 0; y < dst_height - 1; y++) {
+	for (y = 0; y < dst_height; y++) {
 		register unsigned char r = 0, g = 0, b = 0, a = 0;
 		const int iLeft = contrib->ContribRow[y].Left;
 		const int iRight = contrib->ContribRow[y].Right;
@@ -1014,7 +1014,7 @@ static inline int _gdScaleVert (const gdImagePtr pSrc, const unsigned int src_wi
 		return 0;
 	}
 	/* scale each column */
-	for (u = 0; u < dst_width - 1; u++) {
+	for (u = 0; u < dst_width; u++) {
 		_gdScaleCol(pSrc, src_width, pDst, dst_width, dst_height, u, contrib);
 	}
 	_gdContributionsFree(contrib);

ext/gd/tests/bug79676.phpt

@@ -0,0 +1,31 @@
+--TEST--
+Bug #79676 (imagescale adds black border with IMG_BICUBIC)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+function test($image, $desc)
+{
+    echo "$desc - Test Result: ",
+        (imagecolorat($image, imagesx($image) - 1 , imagesy($image) - 1) != 0x000000 ? 'pass' : 'fail'),
+        PHP_EOL;
+}
+
+$size = 32;
+$src = imagecreatetruecolor($size, $size);
+imagefilledrectangle($src, 0, 0, $size - 1 , $size - 1, 0xff00ff);
+
+test($src, 'No scaling');
+test(imagescale($src, $size * 2, $size * 2), 'Scale 200%, default mode');
+test(imagescale($src, $size / 2, $size / 2), 'Scale 50%, default mode');
+test(imagescale($src, $size * 2, $size * 2, IMG_BICUBIC), 'Scale 200%, IMG_BICUBIC mode');
+test(imagescale($src, $size / 2, $size / 2, IMG_BICUBIC), 'Scale 50%, IMG_BICUBIC mode');
+?>
+--EXPECT--
+No scaling - Test Result: pass
+Scale 200%, default mode - Test Result: pass
+Scale 50%, default mode - Test Result: pass
+Scale 200%, IMG_BICUBIC mode - Test Result: pass
+Scale 50%, IMG_BICUBIC mode - Test Result: pass