source: nanovis/tags/1.1.1/shaders/velocityslicevp.cg

/* -*- mode: c++; c-basic-offset: 4; indent-tabs-mode: nil -*- */

#include "particle_common.cg"

void vpmain(in float4 posin : POSITION,
            in float4 colin : COLOR0,
            out float4 posout : POSITION,
            out float4 colout : COLOR0,
            out float2 center : TEXCOORD2,
            out float4 rotation : TEXCOORD3,
            out float4 pointSize : PSIZE,
            uniform sampler3D vfield : TEXUNIT1,
            uniform float tanHalfFOV,
            uniform float4x4 modelview,
            uniform float4x4 mvp)
{
    float4 vec;
    vec.xyz = posin.xyz;
    vec.w = 1.0;

    // length
    // the scale of from bottom to top 
    float3 velocity = tex3D(vfield, vec.xyz).yzw * 2 - float3(1, 1, 1);

    // bottom to top
    // scale
    center.y = ((((int) (length(velocity.xyz) * 511)) / SUBIMAGE_SIZE_Y) * SUBIMAGE_SIZE_Y) / 512.0;

    velocity = mul(modelview, float4(velocity.x, velocity.y, velocity.z, 0.0)).xyz;
    if (length(velocity) != 0.0)
        velocity = normalize(velocity);

    float a = (asin(velocity.z) / 3.141592 + 1) * 0.5;
    center.x = ((((int) (a * 511)) / SUBIMAGE_SIZE_X) * SUBIMAGE_SIZE_X) / 512.0;

    if ((abs(velocity.x) == 0.0) && (abs(velocity.y) == 0.0)) {
        rotation.x = 1;
        rotation.y = 0;
        rotation.z = 0;
        rotation.w = 1; 
    } else {
        float2 xy = normalize(velocity.xy);
        rotation.x = xy.x * 0.8;
        rotation.y = -xy.y * 0.8;
        rotation.z = xy.y * 0.8;
        rotation.w = xy.x * 0.8;
    }

    float4 posEye =  mul(modelview, posin);
    //pointSize = tanHalfFOV / -posEye.z / 5;
    //pointSize = tanHalfFOV / -posEye.z / 10; //j-wire
    pointSize = 20; //0 / -posEye.z;

    posout = mul(mvp, vec);

    colout = colin;
}