/*
 * ======================================================================
 *  AUTHOR:  Wei Qiao <qiaow@purdue.edu>
 *           Purdue Rendering and Perceptualization Lab (PURPL)
 *
 *  Copyright (c) 2004-2006  Purdue Research Foundation
 *
 *  See the file "license.terms" for information on usage and
 *  redistribution of this file, and for a DISCLAIMER OF ALL WARRANTIES.
 * ======================================================================
 */

// update positions based on velocity

#include "common.cg"

float4 main(in float2 uv : TEXCOORD0,
            uniform samplerRECT pos_tex,
            uniform sampler3D vel_tex,
            uniform float timestep,
            uniform float3 scale
            ) : COLOR
{

    // get previous position and velocity
    float4 pos = texRECT(pos_tex, uv);
    float4 ret;
    float time = pos.w;

    float4 vel = float4(tex3D(vel_tex, pos.xyz).xyz, 0);

    //reconstruct negative value
    vel = (vel - float4(0.5,0.5,0.5,0.))*2.;
    vel.x *= scale.x;
    vel.y *= scale.y;
    vel.z *= scale.z;
    ret = pos + vel*timestep;
    //ret = pos;


    //not drawing if the particle is out of bound
    if(ret.x<0 || ret.x>1 || ret.y<0 || ret.y>1 || ret.z<0 || ret.z>1 || time==0)
      ret = float4(1,0,0,0); 
    else
      ret.w = 1;


   // ret.w = 1.;
    return ret;
}