问题描述
I'm noticing that some of the things that I do with images in my app, I could be doing with CALayer properties instead (i.e. borders, shadows, gradients, and so on). So I'm wondering, in general, is it a better idea to use CALayers and such, or just do all that stuff in photoshop and use UIImage(View)s for whatever I need? Scrolling performance has been kinda slow with drop shadows and stuff, so I'm basically trying to find every little optimization that I can.
Background information: I'm basically just scrolling through a bunch of images, vertically. Somewhat like the photos app. This is all from 3.2 onwards, so I have access to things like the shadow and shouldRasterize properties in CALayer.
解决方案A key thing to know about CALayer shadows is that they are, by default, rendered from the layer's composited alpha channel; that can be really slow, particularly when the layer is rotating or changing size. You should look into the shadowPath property: if you give Core Animation a simple shape, such as a rectangle (UIBezierPath +bezierPathWithRect: with the layer's bounds will give you [via its CGPath property] a CGPathRef you can use there), you'll see much better performance.
shouldRasterize is also definitely useful, particularly with views that have many subviews that don't change often; make sure, though, that you set the layer's rasterizationScale to [UIScreen mainScreen].scale, or you'll get some nasty pixelation on high-resolution screens like the iPhone 4's.