采用了openGL的视图3D切换效果，精选ios编程学习源码，很好的参考资料。-The view 3D switching effect of openGL, selection of learning IOS programming source code, a good reference.

The goal of this project is to create a UIView that can generate smooth lines from touch input in a reasonably fast manner without moving to a more complex framework like OpenGL. Update: Completely re-written smooth line algorithm to use native

ios钢笔签名view，使用opengl画的(iOS Signature Capture Demo)