I hope my english is comprehensible...

I need to keystone a video on a curved surface. The classic 4 corner pin keystoning isn't suitable for my needs, since I also need to correct the distortion of the plane on the projection surface.

I thought that a nurb with a video-texture would have been a solution so I downloaded the Jitter Recipes Book n°2 and messed with the Recipe 18: Manipulator, to learn the basics.

The patch is almost perfect, but the control point grid generated by the message exprfill "snorm[0]" is not a linear grid. You could see it by activating the "draw as mesh" toggle. It's a grid that is somewhat larger on the sides and narrower at centre. In fact, the attached video texture has a slight barrel distortion.

I tried to change the message, but I couldn't figure out what is the right function to generate a simple equidistant grid of control points. Can someone help me?

My patch is very similar to Recipe 18, but, here it is anyway: