Playing video with many particles animated on top

问题:

I am playing a movie using an AVPlayer and animating 500 falling particles on top. I tried to simply add 500 animated CALAyers. I tried several variations on that but performance is always a problem. As soon as I get more then around 100 CALayers, the video gets choppy. What would be the proper way to do this? I thought maybe this should be done using OpenGL, but I never used it and can't find how to have a video played in OpenGL. I can get the background videos as separate frame pngs, but being fullscreen, the content size gets quite big quite fast.

回答1:

Try drawing the particles into a much smaller number of CALayers, multiple particles per layer bitmap, one for each speed of falling, etc. Then redraw the layers in background threads as needed so as not to impact the composited on video frame rate.

回答2:

Take a look at this post Alternatives to creating an openGL texture from a captured video frame to overlay an openGL view over video? (iPhone). Brad shows how to render video to OpenGL textures. You can then render your particles over a video textured plane. For interaction, you could integrate a physics engine such as Bullet to exert forces to areas of the screen to interact with the particles.

If you can wait, I think this will get much easier (video to texture stream) in iOS5.

回答3:

We ended up running an OpenGL layer using Cocos2D over our video animation. The performance was impacted a little but for our need, it was alright.