Fix PHP bug #64641: imagefilledpolygon doesn't draw horizontal line

As reported in <https://bugs.php.net/64641> 1-dimensional horizontal
filled polygons are not drawn at all. That is caused by the scanline
algorithm used for drawing filled polygons which skips the drawing of
horizontal edges, because that is normally not necessary. If, however,
the polygon consists of horizontal edges only, that obviously doesn't
work, so we add a special case handling.

6 files changed, 66 insertions, 2 deletions

diff --git a/src/gd.c b/src/gd.c
index ef9908d..c9eca85 100644
--- a/src/gd.c
+++ b/src/gd.c
@@ -3142,6 +3142,19 @@ BGD_DECLARE(void) gdImageFilledPolygon (gdImagePtr im, gdPointPtr p, int n, int
 			maxy = p[i].y;
 		}
 	}
+	/* necessary special case: horizontal line */
+	if (n > 1 && miny == maxy) {
+		x1 = x2 = p[0].x;
+		for (i = 1; (i < n); i++) {
+			if (p[i].x < x1) {
+				x1 = p[i].x;
+			} else if (p[i].x > x2) {
+				x2 = p[i].x;
+			}
+		}
+		gdImageLine(im, x1, miny, x2, miny, c);
+		return;
+	}
 	pmaxy = maxy;
 	/* 2.0.16: Optimization by Ilia Chipitsine -- don't waste time offscreen */
 	/* 2.0.26: clipping rectangle is even better */
diff --git a/tests/gdimagefilledpolygon/.gitignore b/tests/gdimagefilledpolygon/.gitignore
index 9caf98f..9826ed8 100644
--- a/tests/gdimagefilledpolygon/.gitignore
+++ b/tests/gdimagefilledpolygon/.gitignore
@@ -3,3 +3,4 @@
 /gdimagefilledpolygon1
 /gdimagefilledpolygon2
 /gdimagefilledpolygon3
+/php_bug_64641
diff --git a/tests/gdimagefilledpolygon/CMakeLists.txt b/tests/gdimagefilledpolygon/CMakeLists.txt
index 8180bb1..3147a5a 100644
--- a/tests/gdimagefilledpolygon/CMakeLists.txt
+++ b/tests/gdimagefilledpolygon/CMakeLists.txt
@@ -4,6 +4,7 @@ LIST(APPEND TESTS_FILES
 	gdimagefilledpolygon2
 	gdimagefilledpolygon3
 	bug00100
+	php_bug_64641
 )
 
 ADD_GD_TESTS()
diff --git a/tests/gdimagefilledpolygon/Makemodule.am b/tests/gdimagefilledpolygon/Makemodule.am
index 2dcded0..7a2f681 100644
--- a/tests/gdimagefilledpolygon/Makemodule.am
+++ b/tests/gdimagefilledpolygon/Makemodule.am
@@ -4,7 +4,8 @@ libgd_test_programs += \
 	gdimagefilledpolygon/gdimagefilledpolygon0 \
 	gdimagefilledpolygon/gdimagefilledpolygon1 \
 	gdimagefilledpolygon/gdimagefilledpolygon2 \
-	gdimagefilledpolygon/gdimagefilledpolygon3
+	gdimagefilledpolygon/gdimagefilledpolygon3 \
+	gdimagefilledpolygon/php_bug_64641
 endif
 
 EXTRA_DIST += \
@@ -13,4 +14,5 @@ EXTRA_DIST += \
 	gdimagefilledpolygon/gdimagefilledpolygon0.png \
 	gdimagefilledpolygon/gdimagefilledpolygon1.png \
 	gdimagefilledpolygon/gdimagefilledpolygon2.png \
-	gdimagefilledpolygon/gdimagefilledpolygon3.png
+	gdimagefilledpolygon/gdimagefilledpolygon3.png \
+	gdimagefilledpolygon/php_bug_64641.png
diff --git a/tests/gdimagefilledpolygon/php_bug_64641.c b/tests/gdimagefilledpolygon/php_bug_64641.c
new file mode 100644
index 0000000..baf8913
--- /dev/null
+++ b/tests/gdimagefilledpolygon/php_bug_64641.c
@@ -0,0 +1,47 @@
+/*
+	Test drawing of 1-dimensional filled polygons
+
+	We're drawing a vertical and a horizontal 1-dimensional filled polygon,
+	which is supposed to result in a vertical and a horizontal line.
+
+	See also <https://bugs.php.net/64641>.
+*/
+
+#include "gd.h"
+#include "gdtest.h"
+
+int main()
+{
+	gdImagePtr im;
+	gdPointPtr points;
+
+	im = gdImageCreateTrueColor(640, 480);
+
+	points = (gdPointPtr)calloc(3, sizeof(gdPoint));
+	gdTestAssert(points != NULL);
+
+	/* vertical line */
+	points[0].x = 100;
+	points[0].y = 100;
+	points[1].x = 100;
+	points[1].y = 200;
+	points[2].x = 100;
+	points[2].y = 300;
+	gdImageFilledPolygon(im, points, 3, 0xFFFF00);
+
+	/* horizontal line */
+	points[0].x = 300;
+	points[0].y = 200;
+	points[1].x = 400;
+	points[1].y = 200;
+	points[2].x = 500;
+	points[2].y = 200;
+	gdImageFilledPolygon(im, points, 3, 0xFFFF00);
+
+	gdAssertImageEqualsToFile("gdimagefilledpolygon/php_bug_64641.png", im);
+
+	free(points);
+	gdImageDestroy(im);
+
+	return gdNumFailures();
+}
diff --git a/tests/gdimagefilledpolygon/php_bug_64641.png b/tests/gdimagefilledpolygon/php_bug_64641.png
new file mode 100644
index 0000000..62fb621
--- /dev/null
+++ b/tests/gdimagefilledpolygon/php_bug_64641.png