I really like the mesh of the terrain from the screenshot (in terms of usability for video games)!
However, I think the terrain really needs triplanar texture mapping, the stretched texture on the slopes if not up to date.
Btw. just saw the following part of your code:
VECTOR n;
n.x = 2.0*(c_.red-128);
n.y = 2.0*(c_.green-128);
n.z = 2.0*(c_.blue-128);
//normalize to 0-1
vec_normalize(n,1);
//get Euler angle
ANGLE rotation;
vec_rotate(n,vector(0,-90,0));
vec_to_angle(rotation,n);
//if angle is between given angles, paint blendmap
if(abs(rotation.tilt)>gradient_min_ && abs(rotation.tilt)<gradient_max_)
Basically you are only interested in the z-component of the normal vector, aren't you? If it's 1 your rotation.tilt is 0, near 1 the slope is near 90° in incline. Thus you should be able to skip the whole (vec_to_)angle stuff and work with the normal vector directly.
