OpenSim-Test/OpenSim/Region/Framework/Scenes/TerrainUtil.cs

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 */

using System;
using OpenSim.Region.Framework.Interfaces;

namespace OpenSim.Region.Framework.Scenes
{
    public static class TerrainUtil
    {
        public static double MetersToSphericalStrength(double size)
        {
            //return Math.Pow(2, size);
            return (size + 1) * 1.35; // MCP: a more useful brush size range
        }

        public static double SphericalFactor(double x, double y, double rx, double ry, double size)
        {
            return size * size - ((x - rx) * (x - rx) + (y - ry) * (y - ry));
        }

        public static double GetBilinearInterpolate(double x, double y, ITerrainChannel map)
        {
            int w = map.Width;
            int h = map.Height;

            if (x > w - 2.0)
                x = w - 2.0;
            if (y > h - 2.0)
                y = h - 2.0;
            if (x < 0.0)
                x = 0.0;
            if (y < 0.0)
                y = 0.0;

            const int stepSize = 1;
            double h00 = map[(int) x, (int) y];
            double h10 = map[(int) x + stepSize, (int) y];
            double h01 = map[(int) x, (int) y + stepSize];
            double h11 = map[(int) x + stepSize, (int) y + stepSize];
            double a00 = h00;
            double a10 = h10 - h00;
            double a01 = h01 - h00;
            double a11 = h11 - h10 - h01 + h00;
            double partialx = x - (int) x;
            double partialy = y - (int) y;
            double hi = a00 + (a10 * partialx) + (a01 * partialy) + (a11 * partialx * partialy);
            return hi;
        }

        private static double Noise(double x, double y)
        {
            int n = (int) x + (int) (y * 749);
            n = (n << 13) ^ n;
            return (1.0 - ((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0);
        }

        private static double SmoothedNoise1(double x, double y)
        {
            double corners = (Noise(x - 1, y - 1) + Noise(x + 1, y - 1) + Noise(x - 1, y + 1) + Noise(x + 1, y + 1)) / 16;
            double sides = (Noise(x - 1, y) + Noise(x + 1, y) + Noise(x, y - 1) + Noise(x, y + 1)) / 8;
            double center = Noise(x, y) / 4;
            return corners + sides + center;
        }

        private static double Interpolate(double x, double y, double z)
        {
            return (x * (1.0 - z)) + (y * z);
        }

        public static double InterpolatedNoise(double x, double y)
        {
            int integer_X = (int) (x);
            double fractional_X = x - integer_X;

            int integer_Y = (int) y;
            double fractional_Y = y - integer_Y;

            double v1 = SmoothedNoise1(integer_X, integer_Y);
            double v2 = SmoothedNoise1(integer_X + 1, integer_Y);
            double v3 = SmoothedNoise1(integer_X, integer_Y + 1);
            double v4 = SmoothedNoise1(integer_X + 1, integer_Y + 1);

            double i1 = Interpolate(v1, v2, fractional_X);
            double i2 = Interpolate(v3, v4, fractional_X);

            return Interpolate(i1, i2, fractional_Y);
        }

        public static double PerlinNoise2D(double x, double y, int octaves, double persistence)
        {
            double total = 0.0;

            for (int i = 0; i < octaves; i++)
            {
                double frequency = Math.Pow(2, i);
                double amplitude = Math.Pow(persistence, i);

                total += InterpolatedNoise(x * frequency, y * frequency) * amplitude;
            }
            return total;
        }
    }
}