Merge pull request #3142 from radarhere/ellipse

Changed ellipse point calculations to be more evenly distributed

Author: hugovk

Tests/test_imagedraw.py

@@ -169,6 +169,16 @@ def test_ellipse_edge(self):
         self.assert_image_similar(
             im, Image.open("Tests/images/imagedraw_ellipse_edge.png"), 1)
 
+    def test_ellipse_symmetric(self):
+        for bbox in [
+            (25, 25, 76, 76),
+            (25, 25, 75, 75)
+        ]:
+            im = Image.new("RGB", (101, 101))
+            draw = ImageDraw.Draw(im)
+            draw.ellipse(bbox, fill="green", outline="blue")
+            self.assert_image_equal(im, im.transpose(Image.FLIP_LEFT_RIGHT))
+
     def helper_line(self, points):
         # Arrange
         im = Image.new("RGB", (W, H))

src/libImaging/Draw.c

@@ -732,6 +732,29 @@ ImagingDrawBitmap(Imaging im, int x0, int y0, Imaging bitmap, const void* ink,
 #define CHORD 1
 #define PIESLICE 2
 
+static void
+ellipsePoint(int cx, int cy, int w, int h,
+             float i, int *x, int *y)
+{
+    float i_cos, i_sin;
+    float x_f, y_f;
+    double modf_int;
+    i_cos = cos(i*M_PI/180);
+    i_sin = sin(i*M_PI/180);
+    x_f = (i_cos * w/2) + cx;
+    y_f = (i_sin * h/2) + cy;
+    if (modf(x_f, &modf_int) == 0.5) {
+        *x = i_cos > 0 ? FLOOR(x_f) : CEIL(x_f);
+    } else {
+        *x = FLOOR(x_f + 0.5);
+    }
+    if (modf(y_f, &modf_int) == 0.5) {
+        *y = i_sin > 0 ? FLOOR(y_f) : CEIL(y_f);
+    } else {
+        *y = FLOOR(y_f + 0.5);
+    }
+}
+
 static int
 ellipse(Imaging im, int x0, int y0, int x1, int y1,
         float start, float end, const void* ink_, int fill,
@@ -781,8 +804,7 @@ ellipse(Imaging im, int x0, int y0, int x1, int y1,
             if (i > end) {
                 i = end;
             }
-            x = FLOOR((cos(i*M_PI/180) * w/2) + cx + 0.5);
-            y = FLOOR((sin(i*M_PI/180) * h/2) + cy + 0.5);
+            ellipsePoint(cx, cy, w, h, i, &x, &y);
             if (i != start)
                 add_edge(&e[n++], lx, ly, x, y);
             else
@@ -812,8 +834,7 @@ ellipse(Imaging im, int x0, int y0, int x1, int y1,
             if (i > end) {
                 i = end;
             }
-            x = FLOOR((cos(i*M_PI/180) * w/2) + cx + 0.5);
-            y = FLOOR((sin(i*M_PI/180) * h/2) + cy + 0.5);
+            ellipsePoint(cx, cy, w, h, i, &x, &y);
             if (i != start)
                 draw->line(im, lx, ly, x, y, ink);
             else