Why is UIBezierPath faster than CAShapeLayer

Question

I have been experimenting with drawing maps. I drew a map of the United States as a series of UIBezierPath's (one path for each state - converted an SVG file with PaintCode). At the same time I was working with CAShapeLayer's and was amazed at how fast they were. I decided to convert the UIBezierPath to a CAShapeLayer. It ended up being extremely slow. The view would stutter even when I rotated the device. Does anyone know why it would be so slow? It seems that whenever I fill a view with too many CAShapeLayer's it slows the application down tremendously.

This is not a code specific problem, I am just wondering if there are limitations to the amount of CALayer's you can use in an application.

Answer 1

The CAShapeLayer is mostly used to create shapes that you would animate. So when you use it each modification is animated. I don't know UIBezierPath but CAShapeLayer also use antialiasing during rasterization and that would require offscreen rendering that is an expensive task.

Answer 2

offscreen rendering includes shouldRasterize（光栅化） masks（遮罩） shadows（阴影） edge antialiasing（抗锯齿） group opacity（不透明） so if you turn off opaque&shadows and turn on rasterise it will be quicker.you will feel the difference. but still slow the application.