How can I set vector mask for clicking in Qt?

Question

I need create clickable component with custom shape. Appearance is set by svg file. Clickable area must be constrained by svg shape. I find great example of what I need, but it use pixel mask or circle mask. Can you help me find solution?

Answer 1

Most probably you will need to create a pixel mask yourself from the SVG shape.

The question is how to approach this. Qt does not offer a simple way of doing it. However, in Qt you can render the SVG offscreen into an image that you initialize with transparent pixels or a color key. You can then use this image as a mask. If the size of your viewpoint changes frequently, you might want to do the mask rendering in a higher resolution first and then scale it down accordingly for performance. Also note that if your SVG is animated, you would have to accomodate for that.

Or you might use a different library than Qt to obtain the mask. Also, if your SVG contains only a single polygon, you might go for a point-polygon test. But I doubt it, and such a test is also not trivial when the polygon is non-convex (you typically end up with a scanline algorithm anyways).