public static float CosInterpolate(float v1, float v2, float a) {
var angle = a * PI;
var prc = (1.0f - LookupCos(angle)) * 0.5f;
return v1 * (1.0f - prc) + v2 * prc;
}
public static float PerlinNoise2D(int seed, float persistence, int octave, float x, float y) {