Polygonal selection tool allows for the drawing of any arbitrary
polygonal shape. It tracks clicked points in a vector, upon double
clicking we finalize the polygon and generate the selection mask. The
user can press the escape key during selection to cancel.
The mask is generated as follows:
- First we calculate the size of the bounding rect needed to hold the
polygon
- We add 2 pixels to height/width to allow us a 1 pixel border, the
polygon will be centered in this bitmap
- Draw the polygon into the bitmap via Gfx::Painter, making sure to
connect final polygon point to the first to ensure an enclosed shape
- Generate a selection mask the size of the bitmap, with all pixels
initially selected
- Perform a flood fill from (0,0) which is guaranteed to be outside the
polygon
- For every pixel reached by the flood fill, we clear the selected pixel
from the selection mask
- Finally we merge the selection mask like other selection tools.
