Calculates the union of two rectangles.
| x1 |
origin of first rectangle |
| y1 |
origin of first rectangle |
| width1 |
width of first rectangle |
| height1 |
height of first rectangle |
| x2 |
origin of second rectangle |
| y2 |
origin of second rectangle |
| width2 |
width of second rectangle |
| height2 |
height of second rectangle |
| dest_x |
return location for origin of union, or null |
| dest_y |
return location for origin of union, or null |
| dest_width |
return location for width of union, or null |
| dest_height |
return location for height of union, or null |