Fix #319: gdImageRotateInterpolated can have wrong background color

We backport the fix for <https://bugs.php.net/65070>, and also the fix for
<https://bugs.php.net/70976> which was introduced by fixing 65070.

src/gd.c

@@ -4385,6 +4385,12 @@ BGD_DECLARE(int) gdImagePaletteToTrueColor(gdImagePtr src)
 	src->pixels = NULL;
 	src->alphaBlendingFlag = 0;
 	src->saveAlphaFlag = 1;
+
+	if (src->transparent >= 0) {
+		const unsigned char c = src->transparent;
+		src->transparent =  gdTrueColorAlpha(src->red[c], src->green[c], src->blue[c], src->alpha[c]);
+	}
+
 	return 1;
 
 clean_on_error:

src/gd_interpolation.c

@@ -1686,13 +1686,6 @@ gdImageRotateNearestNeighbour(gdImagePtr src, const float degrees,
 	gdRect bbox;
 	int new_height, new_width;
 
-	/* impact perf a bit, but not that much. Implementation for palette
-	   images can be done at a later point.
-	*/
-	if (src->trueColor == 0) {
-		gdImagePaletteToTrueColor(src);
-	}
-
     gdRotatedImageSize(src, degrees, &bbox);
     new_width = bbox.width;
     new_height = bbox.height;
@@ -1750,13 +1743,6 @@ gdImageRotateGeneric(gdImagePtr src, const float degrees, const int bgColor)
 		return NULL;
 	}
 
-	/* impact perf a bit, but not that much. Implementation for palette
-	   images can be done at a later point.
-	*/
-	if (src->trueColor == 0) {
-		gdImagePaletteToTrueColor(src);
-	}
-
 	if (src->interpolation == NULL) {
 		gdImageSetInterpolationMethod(src, GD_DEFAULT);
 	}
@@ -1807,6 +1793,16 @@ BGD_DECLARE(gdImagePtr) gdImageRotateInterpolated(const gdImagePtr src, const fl
 		return NULL;
 	}
 
+	/* impact perf a bit, but not that much. Implementation for palette
+	   images can be done at a later point.
+	*/
+	if (src->trueColor == 0) {
+		if (bgcolor < gdMaxColors) {
+			bgcolor =  gdTrueColorAlpha(src->red[bgcolor], src->green[bgcolor], src->blue[bgcolor], src->alpha[bgcolor]);
+		}
+		gdImagePaletteToTrueColor(src);
+	}
+
 	/* 0 && 90 degrees multiple rotation, 0 rotation simply clones the return image and convert it
 	   to truecolor, as we must return truecolor image. */
 	switch (angle_rounded) {

tests/gdimagerotate/.gitignore

@@ -1,2 +1,3 @@
 /bug00067
 /php_bug_64898
+/php_bug_65070

tests/gdimagerotate/CMakeLists.txt

@@ -1,6 +1,7 @@
 LIST(APPEND TESTS_FILES
 	bug00067
 	php_bug_64898
+	php_bug_65070
 )
 
 ADD_GD_TESTS()

tests/gdimagerotate/Makemodule.am

@@ -5,7 +5,8 @@ endif
 
 if HAVE_LIBPNG
 libgd_test_programs += \
-	gdimagerotate/php_bug_64898
+	gdimagerotate/php_bug_64898 \
+	gdimagerotate/php_bug_65070
 endif
 
 EXTRA_DIST += \
@@ -25,4 +26,6 @@ EXTRA_DIST += \
 	gdimagerotate/bug00067_180_exp.png \
 	gdimagerotate/php_bug_64898.png \
 	gdimagerotate/php_bug_64898_exp.png \
+	gdimagerotate/php_bug_65070.gif \
+	gdimagerotate/php_bug_65070_exp.png \
 	gdimagerotate/remirh128.png

tests/gdimagerotate/php_bug_65070.c

@@ -0,0 +1,27 @@
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+	gdImagePtr src, dst;
+	FILE *fp;
+	int black;
+	char *path;
+
+	fp = gdTestFileOpen2("gdimagerotate", "php_bug_65070.gif");
+	src = gdImageCreateFromGif(fp);
+	fclose(fp);
+
+	black = gdImageColorAllocateAlpha(src, 0, 0, 0, 0);
+	dst = gdImageRotateInterpolated(src, 30.0, black);
+
+	path = gdTestFilePath2("gdimagerotate", "php_bug_65070_exp.png");
+    gdAssertImageEqualsToFile(path, dst);
+	gdFree(path);
+
+	gdImageDestroy(src);
+	gdImageDestroy(dst);
+
+	return gdNumFailures();
+}