Fix #73272: imagescale() affects imagesetinterpolation()

We must not permanently change the interpolation method, but rather
have to restore the old method after we're done with scaling the image.

NEWS

@@ -4,6 +4,8 @@ PHP                                                                        NEWS
 
 -GD:
   . Fixed bug #73213 (Integer overflow in imageline() with antialiasing). (cmb)
+  . Fixed bug #73272 (imagescale() is not affected by, but affects
+    imagesetinterpolation()). (cmb)
 
 - Standard:
   . Fixed bug #73203 (passing additional_parameters causes mail to fail). (cmb)

ext/gd/gd.c

@@ -5175,7 +5175,7 @@ PHP_FUNCTION(imagescale)
 	gdImagePtr im_scaled = NULL;
 	int new_width, new_height;
 	long tmp_w, tmp_h=-1, tmp_m = GD_BILINEAR_FIXED;
-	gdInterpolationMethod method;
+	gdInterpolationMethod method, old_method;
 
 	if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "rl|ll", &IM, &tmp_w, &tmp_h, &tmp_m) == FAILURE)  {
 		return;
@@ -5202,9 +5202,12 @@ PHP_FUNCTION(imagescale)
 	new_width = tmp_w;
 	new_height = tmp_h;
 
+	/* gdImageGetInterpolationMethod() is only available as of GD 2.1.1 */
+	old_method = im->interpolation_id;
 	if (gdImageSetInterpolationMethod(im, method)) {
 		im_scaled = gdImageScale(im, new_width, new_height);
 	}
+	gdImageSetInterpolationMethod(im, old_method);
 
 	if (im_scaled == NULL) {
 		RETURN_FALSE;

ext/gd/tests/bug73272.phpt

@@ -0,0 +1,24 @@
+--TEST--
+Bug #73272 (imagescale() is not affected by, but affects imagesetinterpolation())
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+?>
+--FILE--
+<?php
+require_once __DIR__ . DIRECTORY_SEPARATOR . 'func.inc';
+
+$src = imagecreatetruecolor(100, 100);
+imagefilledrectangle($src, 0,0, 99,99, 0xFFFFFF);
+imageellipse($src, 49,49, 40,40, 0x000000);
+
+imagesetinterpolation($src, IMG_NEAREST_NEIGHBOUR);
+imagescale($src, 200, 200, IMG_BILINEAR_FIXED);
+$dst = imagerotate($src, 60, 0xFFFFFF);
+
+test_image_equals_file(__DIR__ . DIRECTORY_SEPARATOR . 'bug73272.png', $dst);
+?>
+===DONE===
+--EXPECT--
+The images are equal.
+===DONE===