Shader and compositor curve nodes change their inputs even if they are
at identity settings.
That is because shader and compositor curve nodes evaluate their curve
map texture samplers at the normalized input directly, disregarding the
fact that the samplers are evaluated using linear interpolation. This
causes the output to be slightly different that it should be.
This patch remaps the evaluation parameters such that the texture
sampler is evaluated at the center of the pixels.
Differential Revision: https://developer.blender.org/D15811
Reviewed By: Clement Foucault
77a4bb02cc