extmod/modframebuf: Fix 0 radius bug in FrameBuffer.ellipse.

This fixes a bug in FrameBuffer.ellipse where it goes into an infinite loop
if both radii are 0.

This fixes the bug with a simple pre-check to see if both radii are 0, and
in that case sets a single pixel at the center. This is consistent with the
behaviour of the method when called with just one of the radii set to 0,
where it will draw a horizontal or vertical line of 1 pixel width.

The pixel is set with setpixel_checked so it should handle out-of-bounds
drawing correctly.

This fix also includes three new tests: one for the default behaviour, one
for drawing out-of-bounds, and one for when the sector mask is 0.

Fixes issue #16053.

Signed-off-by: Corran Webster <cwebster@unital.dev>

3 files changed, 115 insertions, 0 deletions

diff --git a/extmod/modframebuf.c b/extmod/modframebuf.c
index cd0f50d104..b718a66cc6 100644
--- a/extmod/modframebuf.c
+++ b/extmod/modframebuf.c
@@ -536,6 +536,10 @@ static mp_obj_t framebuf_ellipse(size_t n_args, const mp_obj_t *args_in) {
     } else {
         mask |= ELLIPSE_MASK_ALL;
     }
+    if (args[2] == 0 && args[3] == 0) {
+        setpixel_checked(self, args[0], args[1], args[4], mask & ELLIPSE_MASK_ALL);
+        return mp_const_none;
+    }
     mp_int_t two_asquare = 2 * args[2] * args[2];
     mp_int_t two_bsquare = 2 * args[3] * args[3];
     mp_int_t x = args[2];
diff --git a/tests/extmod/framebuf_ellipse.py b/tests/extmod/framebuf_ellipse.py
index a4c784aff8..ec0461e66c 100644
--- a/tests/extmod/framebuf_ellipse.py
+++ b/tests/extmod/framebuf_ellipse.py
@@ -63,3 +63,18 @@ for x, y in (
     fbuf.fill(0)
     fbuf.ellipse(x, y, 6, 12, 0xAA, True)
     printbuf()
+
+# Draw an ellipse with both radius 0
+fbuf.fill(0)
+fbuf.ellipse(15, 15, 0, 0, 0xFF, True)
+printbuf()
+
+# Draw an ellipse with both radius 0 out of bounds
+fbuf.fill(0)
+fbuf.ellipse(45, 45, 0, 0, 0xFF, True)
+printbuf()
+
+# Draw an ellipse with radius 0 and all sectors masked out
+fbuf.fill(0)
+fbuf.ellipse(15, 15, 0, 0, 0xFF, True, 0)
+printbuf()
diff --git a/tests/extmod/framebuf_ellipse.py.exp b/tests/extmod/framebuf_ellipse.py.exp
index ae6ad1ee7e..96a60c24da 100644
--- a/tests/extmod/framebuf_ellipse.py.exp
+++ b/tests/extmod/framebuf_ellipse.py.exp
@@ -702,3 +702,99 @@ aaaaaaaaaaaaaaaaaaaaaa00000000000000000000000000000000000000
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