<p>How can I draw a concave corner rectangle in WPF?</p>

```
```
do you mean a rectangle with concave corners?, ie: 
     ____________________
    |                    |
  __|                    |__
 |                          |
 |                          |
 |                          |
 |__                      __|
    |                    |
    |____________________|
```
```
Given a rectangle of dimension
```
w x h
```
with corner radius
```
r
```
There are 4 corners:
```
```
A :  0,0
B :  w,0
C :  w,h
D :  0,h
```
```
There is an implicit minimum size of
```
```
w = 2r
h = 2r
```
```
There are 4 Circle Centers,
```
A,B,C,D
```
And there's thus a grid of edge points:
```
```
(0,0)--(0+r,0)---(w-r,0)---(w,0)
|                              |
(0,0+r)                  (w,0+r)
|                              |
|                              |
(0,h-r)                  (w,h-r)
|                              |
(0,h)--(0+r,h)---(w-r,h)---(w,h)
```
```
Then its merely a case of computing the arc from one point to another.