Test and document filling behavior of self-intersecting polygons

src/gd.c

@@ -3467,8 +3467,8 @@ BGD_DECLARE(void) gdImagePolygon (gdImagePtr im, gdPointPtr p, int n, int c)
  *
  * Parameters:
  *   im - The image.
- *   p  - The vertices.
- *   n  - The number of vertices as array of <gdPoint>s.
+ *   p  - The vertices as array of <gdPoint>s.
+ *   n  - The number of vertices.
  *   c  - The color
  *
  * See also:
@@ -3506,6 +3506,10 @@ BGD_DECLARE(void) gdImageOpenPolygon (gdImagePtr im, gdPointPtr p, int n, int c)
  *
  * Draws a filled polygon
  *
+ * The polygon is filled using the even-odd fillrule what can leave unfilled
+ * regions inside of self-intersecting polygons. This behavior might change in
+ * a future version.
+ *
  * Parameters:
  *   im - The image.
  *   p  - The vertices as array of <gdPoint>s.

tests/gdimagefilledpolygon/.gitignore

@@ -4,3 +4,4 @@
 /gdimagefilledpolygon2
 /gdimagefilledpolygon3
 /php_bug_64641
+/self_intersecting

tests/gdimagefilledpolygon/CMakeLists.txt

@@ -5,6 +5,7 @@ LIST(APPEND TESTS_FILES
 	gdimagefilledpolygon3
 	bug00100
 	php_bug_64641
+	self_intersecting
 )
 
 ADD_GD_TESTS()

tests/gdimagefilledpolygon/Makemodule.am

@@ -5,7 +5,8 @@ libgd_test_programs += \
 	gdimagefilledpolygon/gdimagefilledpolygon1 \
 	gdimagefilledpolygon/gdimagefilledpolygon2 \
 	gdimagefilledpolygon/gdimagefilledpolygon3 \
-	gdimagefilledpolygon/php_bug_64641
+	gdimagefilledpolygon/php_bug_64641 \
+	gdimagefilledpolygon/self_intersecting
 endif
 
 EXTRA_DIST += \
@@ -15,4 +16,5 @@ EXTRA_DIST += \
 	gdimagefilledpolygon/gdimagefilledpolygon1.png \
 	gdimagefilledpolygon/gdimagefilledpolygon2.png \
 	gdimagefilledpolygon/gdimagefilledpolygon3.png \
-	gdimagefilledpolygon/php_bug_64641.png
+	gdimagefilledpolygon/php_bug_64641.png \
+	gdimagefilledpolygon/self_intersecting_exp.png

tests/gdimagefilledpolygon/self_intersecting.c

@@ -0,0 +1,31 @@
+/**
+ * We're testing the filling behavior of self-intersecting polygons, which is
+ * *currently* using the even-odd fillrule.
+ */
+
+
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+    gdImagePtr im;
+    int black;
+    gdPoint points[] = {{50, 5}, {24, 86}, {93, 36}, {7, 36}, {76, 86}};
+    char *path;
+
+    im = gdImageCreate(100, 100);
+    gdImageColorAllocate(im, 255, 255, 255);
+    black = gdImageColorAllocate(im, 0, 0, 0);
+
+    gdImageFilledPolygon(im, points, 5, black);
+
+    path = gdTestFilePath2("gdimagefilledpolygon", "self_intersecting_exp.png");
+    gdAssertImageEqualsToFile(path, im);
+    gdFree(path);
+
+    gdImageDestroy(im);
+
+    return gdNumFailures();
+}