/*

 * 

    Copyright:  Copyright © 2003 Apple Computer, Inc., All Rights Reserved

                Portions Copyright (C) Jason Shankel, 2000"

    Disclaimer: IMPORTANT:  This Apple software is supplied to you by Apple Computer, Inc.

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            copyrights in this original Apple software (the "Apple Software"), to use,

            reproduce, modify and redistribute the Apple Software, with or without

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            The Apple Software is provided by Apple on an "AS IS" basis.  APPLE MAKES NO

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            PURPOSE, REGARDING THE APPLE SOFTWARE OR ITS USE AND OPERATION ALONE OR IN

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 *

 */

#include "faultformation.h"

/*

Returns a random number between v1 and v2

*/

float RangedRandom(float v1,float v2)

{

    return v1 + (v2-v1)*((float)rand())/((float)RAND_MAX);

}

/*

Given a height field, normalize it so that the minimum altitude

is 0.0 and the maximum altitude is 1.0

*/

void NormalizeTerrain(height_field_t field,int size)

{

    float maxVal,minVal,dh;

    int i;

    /*

    Find the maximum and minimum values in the height field

    */ 

    maxVal = field[0];

    minVal = field[0];

    for (i=1;i<size*size;i++)

    {

        if (field[i] > maxVal) 

        {

            maxVal = field[i];

        }

        else if (field[i] < minVal) 

        {

            minVal = field[i];

        }

    }

    /*

    Find the altitude range (dh)

    */

    if (maxVal <= minVal) return;

    dh = maxVal-minVal;

    /*

    Scale all the values so they are in the range 0-1

    */

    for (i=0;i<size*size;i++)

    {

        field[i] = (field[i]-minVal)/dh;

    }

}

/*

Erosion filter -

FilterHeightBand applies a FIR filter across a row or column of the height field

*/

void FilterHeightBand(float *band,int stride,int count,float filter)

{

    int i,j=stride;

    float v = band[0];

    for (i=0;i<count-1;i++)

    {

        band[j] = filter*v + (1-filter)*band[j];

        v = band[j];

        j+=stride;

    }

}

/*

Erosion filter -

Erodes a terrain in all 4 directions

*/

void FilterHeightField(height_field_t field,int size,float filter)

{

    int i;

    /*

    Erode rows left to right

    */

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

    {

        FilterHeightBand(&field[size*i],1,size,filter);

    }

    /*

    Erode rows right to left

    */

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

    {

        FilterHeightBand(&field[size*i+size-1],-1,size,filter);

    }

    /*

    Erode columns top to bottom

    */

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

    {

        FilterHeightBand(&field[i],size,size,filter);

    }

    /*

    Erode columns bottom to top

    */

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

    {

        FilterHeightBand(&field[size*(size-1)+i],-size,size,filter);

    }

}

void MakeTerrainFault(height_field_t field,int size,int iterations,int maxDelta,int minDelta,int iterationsPerFilter,float filter)

{

    int x1,y1,x2,y2,dx1,dy1,dx2,dy2,i,dHeight;

    /*

    Clear the height field

    */

    for (i=0;i<size*size;i++)

    {

        field[i] = 0.0f;

    }

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

    {

        /*

        Calculate the dHeight for this iteration

        (linear interpolation from maxDelta to minDelta

        */

        dHeight = maxDelta - ((maxDelta-minDelta)*i)/iterations;

        /*

        Pick two random points on the field for the line

        (make sure they're not identical)

        */

        x1 = rand()%size;

        y1 = rand()%size;

        do

        {

            x2 = rand()%size;

            y2 = rand()%size;

        }while (x2==x1 && y2==y1);

        /*

        dx1,dy1 is a vector in the direction of the line

        */

        dx1 = x2 - x1;

        dy1 = y2 - y1;

        for (x2 = 0;x2<size;x2++)

        for (y2 = 0;y2<size;y2++)

        {

            /*

            dx2,dy2 is a vector from x1,y1 to the candidate point

            */

            dx2 = x2-x1;

            dy2 = y2-y1;

            /*

            if z component of the cross product is 'up', then elevate this point

            */

            if (dx2*dy1 - dx1*dy2 > 0)

            {

                field[x2+size*y2] += (float)(dHeight);

            }

        }

        /*

        Erode terrain

        */

        if (iterationsPerFilter!=0 && (i%iterationsPerFilter)==0)

            FilterHeightField(field,size,filter);

    }

    /*

    Normalize terrain (height field values in the range 0-1)

    */

    NormalizeTerrain(field,size);

}