/* -*- mode: c++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/*
 * Copyright (c) 2004-2013  HUBzero Foundation, LLC
 *
 * Authors:
 *   Wei Qiao <qiaow@purdue.edu>
 */

// update positions based on velocity

#include "common.cg"

float4 main(in float2 uv : TEXCOORD0,
            uniform samplerRECT pos_tex,
            uniform samplerRECT init_pos_tex,
            uniform sampler3D vel_tex,
            uniform float timestep,
            uniform float max,
            uniform float3 scale) : COLOR
{
    float4 ret;
    // get previous position
    float4 pos = texRECT(pos_tex, uv);
    float time = pos.w;

    if (max > 0) {
#ifdef EXPIRE
        time -= timestep;

        // Lifetime ended?
        if (time < 0) {
            return texRECT(init_pos_tex, uv);
        }
#endif
        //reconstruct negative value
        float4 vel = float4(tex3D(vel_tex, pos.xyz).yzw, 0.0) * 2.0 - float4(1.0, 1.0, 1.0, 0.0);
        vel = vel * max;
        //vel *= float4(scale, 1);
        ret = pos + (vel * timestep);
    } else {
        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) {
        ret = texRECT(init_pos_tex, uv);
    } else {
        ret.w = time;
    }

    return ret;
}