Keystone is a video projection mapping library for Processing. It allows you to warp your Processing sketches onto any flat surface by using corner-pin keystoning, regardless of your projector’s position and orientation. In other words, it warps your graphics in order to compensate for the perspectival distortion that occurs when your projector is off-axis. To get started:
Install keystone from your Processing libraries list.
Or you can also download Keystone from here: http://keystonep5.sourceforge.net/
Install the Keystone library in the libraries folder in your Processing documents directory.
Run the CornerPin example demo that comes with Keystone. Press ‘c’ to enter calibration mode, etc. (examine the keypressed() method in that example for more details.)