问题
I used the scanning line seed filling algorithm to realize the color filling function.
But I don't know how to do that. When my pen lands in the flower, I need to draw only Inside the black edge of the flower,do not draw in the hair.
I have tried to use :
CALayer *layer = [CALayer layer];
layer.contents = (__bridge id)(image.CGImage);
self.drawView.layer.mask = layer;
But the plan didn't work.
if any one gives solution it would be so great,Thank you.
(English is not my native language; please excuse typing errors.)
回答1:
Use a two pass approach.
- Use the same algorithm as the fill algorithm to create a stencil mask which fills the area you want to allow the pen to draw.
- Draw the pen with stencil testing to constrain it to the allowed region.
Similar approach could be used to create an alpha-mask on the fly (e.g. as a texture), and mix that with the pen drawing.
来源：https://stackoverflow.com/questions/54019522/ios-how-to-paint-in-the-within-limits