Crash after calling arc with the width parameter

[jonha892]

Hi,

What did you do?
I get an error if I use the width argument of the arc function. It works fine if I leave out the argument.
I call the function like this:
draw.arc([0+offset/2, 0+offset/2,i_w, i_h], a_s, a_e, fill=c, width=8)

What did you expect to happen?
This should work, since it worked on a different machine 2 months ago

What actually happened?
The script crashes without an error message. I used the python tracer module and it just stops after:

ImageDraw.py(111):                 if self.palette and not isinstance(ink, numbers.Number):
ImageDraw.py(113):                 ink = self.draw.draw_ink(ink, self.mode)
ImageDraw.py(114):             if fill is not None:
ImageDraw.py(120):         return ink, fill
ImageDraw.py(125):         if ink is not None:
ImageDraw.py(126):             self.draw.draw_arc(xy, start, end, ink, width)

What versions of Pillow and Python are you using?

• Python 3.7.3
• PIL 6.1.0
• Windows 10
• anaconda package manager

Is this a local problem or is it a problem with PIL 6.1? I remember it working when I used:

• Python 3.6.8,
• PIL: 5.4
• PIP
• Linux

[radarhere]

Pillow 6.1.0 did include a change to this function - #3824 - so it's possible that something changed.

To help with reproducibility, could you provide a self-contained example? It's conceivable that the specific values you're using for offset etc. are triggering the problem.

[jonha892]

Sure, here is a self-contained example that crashes on my system:

from PIL import Image, ImageDraw
im = Image.new('RGB', (640, 640))
draw = ImageDraw.Draw(im)
draw.arc([0+0/2, 0+0/2, 640.0, 640.0], 72.0, 128.5, fill='#1890ff', width=8)
print('Drew an arc...')

I used the actual values where the bug occurs.
I do draw over the bounds of the image. However, I assumed that it should behave like other functions that allow out-of-bound drawing.

[cgohlke]

This should fix the crash:

diff --git a/src/libImaging/Draw.c b/src/libImaging/Draw.c
index 559be1b0..dee7c524 100644
--- a/src/libImaging/Draw.c
+++ b/src/libImaging/Draw.c
@@ -834,7 +834,7 @@ ellipse(Imaging im, int x0, int y0, int x1, int y1,

         // Build edge list
         // malloc check UNDONE, FLOAT?
-        maxEdgeCount = end - start;
+        maxEdgeCount = ceil(end - start);
         if (inner) {
             maxEdgeCount *= 2;
         }

[radarhere]

Thanks @cgohlke

I've created PR #4014 with the fix.

[hugovk]

Thanks all, merged!