A Qt demo for splitting QGraphicsItem with QGraphics's function: tofillPolgons() and tofillPolgon().
Scenario: we already have annotations for rectangles, circles and polygons, we are going to enable an automatic merge of our shapes to count the number of items currently in the scene.
When dealing with Paths, its performance is not good (0.5-1s).
I keep trace of the eraser and calculate a segment between the starting and finishing points. Then I divide the item into a left and a right part based on the side they are.
For an ellipse,
For a rect,
Merging paths is a special requirement, I used PainterPath's operator "+" to achieve it.
Its behavior is like following figures.
