"You are saying that normal is always stands in 90 degrees, what you mean by that?" =>

Suppose that you have two vectors, v1 and v2. Then your angle can be calculated as follows:
my_angle = acos((v1.x*v2.x+v1.y*v2.y+v1.z*v2.z)/(vec_length(v1)*vec_length(v2));

Thank you so much Superku
Just one more question, where do I get that two vectors?
I need to set surface's angle, to do not allow player climb surfaces with a high angle.
So I'll use 'c_trace' to detect surface under player's feet (normal (only now I got what was meant by "right angle", really hard to learn Maths in English for me)).
But where do I get two vector's? Thank you one more time.

Save the normal from your gravity trace in another VECTOR, f.i.
VECTOR normal_save;
...
c_trace(...)
vec_set(normal_save,normal);

When you now collide with a wall, the normal vector will be set to the collision surface's normal. Compare those two vectors.


Besides, you do not need to do that at all, because you normally only trace vertically down (or up). Then just check the normal.z value of the wall (see manual).

Thank you Superku, but manual says that normal.z can be between 1 and -1 only.
And what is "ceiling plane"? I tried to translate it into my mother language, but it translate it as a celling...
If I need to prevent player climbing surfaces with big angle, do I need to make sure that normal.z is bigger that 0.5? Thank you one more time.

"do I need to make sure that normal.z is bigger that 0.5?"

Exactly! But don't forget you only have to do that when you collide with a wall, otherwise normal.z can have random values from previous c_trace/ c_move instructions.

So I'll need to use EVENT_BLOCK too detect colliding, and I right?