Fix #585: gdTransformAffineCopy() changes interpolation method

We have to properly initialize `interpolation_id_bak`.

4 files changed, 37 insertions, 1 deletions

diff --git a/tests/gdtransformaffinecopy/.gitignore b/tests/gdtransformaffinecopy/.gitignore
index a6b56ec..632fc5d 100644
--- a/tests/gdtransformaffinecopy/.gitignore
+++ b/tests/gdtransformaffinecopy/.gitignore
@@ -1 +1,2 @@
 /github_bug_00583
+/github_bug_00585
diff --git a/tests/gdtransformaffinecopy/CMakeLists.txt b/tests/gdtransformaffinecopy/CMakeLists.txt
index 69472fb..b2d47c8 100644
--- a/tests/gdtransformaffinecopy/CMakeLists.txt
+++ b/tests/gdtransformaffinecopy/CMakeLists.txt
@@ -1,5 +1,6 @@
 LIST(APPEND TESTS_FILES
 	github_bug_00583
+	github_bug_00585
 )
 
 ADD_GD_TESTS()
diff --git a/tests/gdtransformaffinecopy/Makemodule.am b/tests/gdtransformaffinecopy/Makemodule.am
index f86b3c9..f03969d 100644
--- a/tests/gdtransformaffinecopy/Makemodule.am
+++ b/tests/gdtransformaffinecopy/Makemodule.am
@@ -1,5 +1,6 @@
 libgd_test_programs += \
-	gdtransformaffinecopy/github_bug_00583
+	gdtransformaffinecopy/github_bug_00583 \
+	gdtransformaffinecopy/github_bug_00585
 
 EXTRA_DIST += \
 	gdtransformaffinecopy/CMakeLists.txt
diff --git a/tests/gdtransformaffinecopy/github_bug_00585.c b/tests/gdtransformaffinecopy/github_bug_00585.c
new file mode 100644
index 0000000..e83910c
--- /dev/null
+++ b/tests/gdtransformaffinecopy/github_bug_00585.c
@@ -0,0 +1,33 @@
+/*
+ * Test that gdTransformAffineCopy() does not change the interpolation method
+ *
+ * See <https://github.com/libgd/libgd/issues/585>
+ */
+
+#include "gd.h"
+#include "gdtest.h"
+
+int main()
+{
+	gdImagePtr src, dst;
+	gdRect rect = {0, 0, 8, 8};
+	double matrix[] = {1, 1, 1, 1, 1, 1};
+	int res;
+	gdInterpolationMethod old_m, new_m;
+
+	src = gdImageCreateTrueColor(8, 8);
+	gdTestAssert(src != NULL);
+	dst = gdImageCreateTrueColor(8, 8);
+	gdTestAssert(dst != NULL);
+
+	res = gdImageSetInterpolationMethod(src, GD_CATMULLROM);
+	gdTestAssert(res == GD_TRUE);
+	old_m = gdImageGetInterpolationMethod(src);
+	gdTransformAffineCopy(dst, 0, 0, src, &rect, matrix);
+	new_m = gdImageGetInterpolationMethod(src);
+	gdTestAssert(new_m == old_m);
+
+	gdImageDestroy(src);
+	gdImageDestroy(dst);
+	return gdNumFailures();
+}