yea, i guess the grid distort is more what you are looking for…

about homography, i would say, its not a bug. homography appears to be a 2-dimensinal transformation, but on the contrary:

the usual transforms we know (scale, rotate, translate, …) are called affine transforms. they are applied to 4d-vectors in homogeneous space (x, y, z, 1), where the 4th component w is always 1. the w component dissapears for the user.

then there are so called perspective transforms like the perspective or vertigo node. this class of transforms alters the w component. after the transformation, the vector is somewhere in 4d-sapce and has to be divided by w, to put it back into our space.

perspective transforms should only be applied to the perspective pin of the renderer, because there the graphics card does the division by w to project the points on the screen.

so if perspective transforms are applied somwhere else, the result should be divided by w.

homography actually is a perspective transform and therefore alters the w component. when applied to texture coordinates it gets even more complicated, because usualy they live in 2d-space…

and a note. there is no affine transform, that can distort a shape irregular, like homography (perspective), or the GridDistort (linear interpolation) does.

here a small patch:

affine_vs_perspective.v4p (10.5 kB)