/*

     File: GeoUtils.c

 Abstract: Utilities for generating height maps.

  Version: 1.3

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 */

#include "GeoUtils.h"

static unsigned int randseed, m_lo, m_hi;

// ---------------------------------------------------------------------

// seed 32 bit RANROT-B PRNG

// ---------------------------------------------------------------------

static inline void rands(int seed){ randseed = m_lo = seed; m_hi = ~seed; }

// ---------------------------------------------------------------------

// get 32 bits of noise

// ---------------------------------------------------------------------

static inline int randi(void) { m_hi = (m_hi<<16) + (m_hi>>16); m_hi += m_lo; m_lo += m_hi; return m_hi; }

// ---------------------------------------------------------------------

// get random float in range [-x..x]

// ---------------------------------------------------------------------

static inline float randf(float x) { return (x * randi() / (float)0x7FFFFFFF); }

float *GenHeightMap(int wide, int deep, int seed)

{

    int i, ni, mi, pmi;

    int j, nj, mj, pmj;

    int w = wide;

    int d = deep;

    float noiseRange = (float)w * 0.5f;

    float r = 0.5;

    float *h = malloc(wide * deep * sizeof(float));

    float *map = calloc(1, wide * deep * sizeof(float) * 6);

    rands(seed);

    h[0] = randf(noiseRange);

    while(w > 0)

    {

        // diamond midpoint displacement

        for (i = 0; i < wide; i += w)

        {

            for (j = 0; j < deep; j += d)

            {

                ni = (i + w) % wide;

                nj = (j + d) % deep;

                mi = (i + w / 2);

                mj = (j + d / 2);

                h[mi + wide * mj] = 

                (h[i  +  j * wide] + 

                 h[ni +  j * wide] + 

                 h[i  + nj * wide] + 

                 h[ni + nj * wide]) * 0.25f + randf(noiseRange);

            }

        }

        // square midpoint displacement

        for (i = 0; i < wide; i += w)

        {

            for (j = 0; j < deep; j += d)

            {

                ni = (i + w) % wide;

                nj = (j + d) % deep;

                mi = (i + w / 2);

                mj = (j + d / 2);

                pmi = (i - w / 2 + wide) % wide;

                pmj = (j - d / 2 + deep) % deep;

                h[mi + j * wide] = 

                (h[i  + j   * wide] + 

                 h[ni + j   * wide] + 

                 h[mi + pmj * wide] + 

                 h[mi + mj  * wide]) * 0.25f + randf(noiseRange);

                h[i + mj * wide] = 

                (h[i   + j  * wide] + 

                 h[i   + nj * wide] + 

                 h[pmi + mj * wide] + 

                 h[mi  + mj * wide]) * 0.25f +  randf(noiseRange);

            }

        }

        // fractal recursion

        w >>= 1;

        d >>= 1;

        noiseRange *= r;

    }

    // gen positions

    for (j = 0; j < deep; j++)

    {

        for (i = 0; i < wide; i++)

        {

            int i0 = j*wide+i;

            float h0 = h[i0];

            map[i0*6 + 0] = i*2-wide;

            map[i0*6 + 1] = j*2-deep;

            map[i0*6 + 2] = h0;

            // gen normals

            if (j < deep-1 && i < wide-1)

            {

                int ih =  j   *wide+i+1;

                int iv = (j+1)*wide+i;

                int id = (j+1)*wide+i+1;

                float dh, dv;

                // add cross product of first tri

                dh = h[ih]-h0;

                dv = h[iv]-h0;

                map[i0*6 + 3] += dh;

                map[i0*6 + 4] += dv;

                map[i0*6 + 5] += 1;

                map[ih*6 + 3] += dh;

                map[ih*6 + 4] += dv;

                map[ih*6 + 5] += 1;

                map[iv*6 + 3] += dh;

                map[iv*6 + 4] += dv;

                map[iv*6 + 5] += 1;

                // add cross product of second tri

                dh = h[id]-h[iv];

                dv = h[id]-h[ih];

                map[id*6 + 3] += dh;

                map[id*6 + 4] += dv;

                map[id*6 + 5] += 10;

                map[ih*6 + 3] += dh;

                map[ih*6 + 4] += dv;

                map[ih*6 + 5] += 1;

                map[iv*6 + 3] += dh;

                map[iv*6 + 4] += dv;

                map[iv*6 + 5] += 1;

            } 

        }

    }

    free(h);

    return map;

}