I'm trying to find the most simple way to put a spherical gradient texture on a plane (square) so that the circle of the gradient and the plane are aligned center to center and the circle fits the plane.
I can do it with the gradient texture but the circle of the gradient just never fits the plane. I read somewhere that the center of the gradient will be where the origin of the geometry is, but I have the origin of the plane in its center, yet the gradient is always off. I could play with the mapping node settings and scale and translate until it more or less fits, but I just can't imagine I need to do it manually, that there isn't a more simple and exact way? I'm using cycles render.
Using the node setup posted by LukeD in his answer, I do get the desired result starting from scratch, using the startup blend file. But with my project file, using the same node setup, the plane remains just black. Then I noticed a tiny little dot of a gradient circle in the middle of the plane, when rendered close up. It's very tiny and even pushing the colour ramp handles extreme to the edge just barely makes it bigger. I have my units setting on metric, with a scale of 0,01 because I work with centimeters. Changing the units to "none" and the scale to "1" did not seem to have any effect on the result. (see screenshot)
I added a mapping node with the "texture" tab clicked and a scale of x1000 to all 3 axes and this fixed the problem, giving the expected result (see screenshot)
So is this a bug? Why is a x1000 scale factor needed (not x100) to make up for a 0,01 scaling?