After deforming the space with a sine function there is no problem in calculating the gradient. The problem is calculating the new correct distance to the neare

After deforming the space with a sine function there is no problem in calculating the gradient. The problem is calculating the new correct distance to the nearest surface after a space transformation. You can see this problem in 2D, here I made an example https://www.shadertoy.com/view/NtsSRf https://www.shadertoy.com/view/NtsSRf