How to use the shouldRasterize attribute to solve the problem of blending and overdrawing GPU views

The GPU has a maximum limit for each pixel that can be drawn (the so-called fill rate). In this case, all the pixels of the entire screen can be easily drawn. However, dropped frames may occur if the same area needs to be constantly redrawn due to overlapping layer relationships.

The GPU will forego drawing pixels that are completely obscured by other layers, but calculating whether a layer is occluded is also quite complicated and consumes processor resources. Also, the resources consumed by merging transparent overlapping pixels (ie, blends) of different layers are also quite objective. Therefore, in order to speed up the processing process, it is not always necessary to use a transparent layer.

In any case, you should do this:

Set a fixed, opaque color for the view's backgroundColor property

Set opaque attribute to YES

This reduces mixing behavior (because the compiler knows that nothing after the layer will have an effect on the final pixel color) and the calculation is accelerated, avoiding overdrawing behavior because Core Animation can discard everything that is completely obscured. Layers, not every pixel.

If you use images, try to avoid transparency unless it is necessary. If the image is to be displayed before a fixed background color or a fixed background image, you do not need to move relative to the foreground. You only need to pre-fill the background image to avoid runtime color mixing.

If it is text, a white background UILabel (or other color) will be more efficient than a transparent background.

Finally, using the shouldRasterize attribute wisely, you can collapse a fixed layer system into a single image so that you do not need to recompose each frame, and there will be no mixing or over-drawing between sublayers. Performance problem.