Texturing a non rectangular quad

I guess what you are calling flip is a change in the tessellation. To avoid that you need to draw two triangles instead of one quad.

if you don't want distortion, one way is to make the grid finer: instead of a quad (which is a 1x1 grid), draw a nxn grid. Remember to draw triangles and not quad to avoid the flip.

what u see is normal, youre applying a quad onto something that is not a quad, it doesnt work, just like trying to wrap a quad texture around a sphere

https://developer.sonyericsson.com/site/global/techsupport/tipstrickscode/java/p_java_0801.jsp

http://www.opengl.org/resources/code/samples/mjktips/projtex/distortion.txt

http://www.r3.nu/~cass/qcoord/

Thanks for the replies!