Nik02 thanks for the hint, you're absolutely right: thinking on the texture maps has completely moved my focus on the problem.
I've just tried with two control points and the result is correct.

Just another question: I've ramps with four, five or six control points, what is the best way to interpolate these control points and achieve a correct result? Bézier curve?
Thanks.

Nik02 thanks for the hint, you're absolutely right: thinking on the texture maps has completely moved my focus on the problem.
I've just tried with two control points and the result is correct.

Just another question: I've ramps with four or five control points, what is the best way to interpolate these control points and achieve a correct result? Bézier curve?
Thanks.

Nik02 thanks for the hint, you're absolutely right: thinking on the texture maps has completely moved my focus on the problem.
I've just tried with two control points and the result is correct.

Just another question: I've ramps with four o five control points, what is the best way to interpolate these control points and achieve a correct result? Bézier curve?
Thanks.