I'm experiencing an interesting distortion in the UV mapping of a trapezoid. When I map a square plane and tilt it backwards, the perspective-correct interpolation gives it the expected pinching at the top, and stretching at the bottom. However, when I scale up the base of a square to make a trapezoid, my UV interpolation shows a noticeable break along the diagonal where the two faces meet:

enter image description here

I've created a working example to demonstrate this effect in JSFiddle. You can rotate the camera to notice the trapezoid doesn't tilt back, so perspective shouldn't really affect the interpolation.

Does this behavior have a name? If so, is there any known solution to it?



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