the best way would be with shaders,
this article is interesting and presents a fairly simple shader
it might take some work on your part to understand how this works though, i dont think anyone will be able to hand you a ready made solution.
do some research on the basics of shaders, GLSL shaders to be precise.
hint though: a shader can only be applied to the drawing one one texture, If you want to ripple your entire screen, you should draw it all to a render texture instead of the screen and then render the rendertexture to the screen with the shader applied, though it will be a lot slower that way!
I was considering doing something like this myself and creating a “post processing” class with which people could write any shader they wanted for the entire screen, but havent gotten to that yet,