// passthrough.vert
#version 120

attribute vec3 position;
varying vec3 vertex;

void main() {
    vertex = position;
    gl_Position = gl_ModelViewProjectionMatrix * vec4(position, 1);
}

// gaussian.frag
#version 120

varying vec3 vertex;

const float gaussD3 = 0.0044318;
const float gaussD2 = 0.0539910;
const float gaussD1 = 0.2419710;
const float gaussD0 = 0.3989423;

uniform sampler3D tex;
uniform vec3 direction;
uniform vec4 color;

// Simple gaussian blur in the specified direction (set direction.x, direction.y, direction.z)
// standard deviation is 1, sample rate is 1 per pixel in a 3 pixel radius
void main() {
    vec4 sum = vec4(0.0);

    sum += texture3D(tex, vec3(vertex.x - 3*direction.x, vertex.y - 3*direction.y, vertex.z - 3*direction.z)) * gaussD3;
    sum += texture3D(tex, vec3(vertex.x - 2*direction.x, vertex.y - 2*direction.y, vertex.z - 2*direction.z)) * gaussD2;
    sum += texture3D(tex, vec3(vertex.x - 1*direction.x, vertex.y - 1*direction.y, vertex.z - 1*direction.z)) * gaussD1;
    sum += texture3D(tex, vec3(vertex.x, vertex.y, vertex.z)) * gaussD0;
    sum += texture3D(tex, vec3(vertex.x + 1*direction.x, vertex.y + 1*direction.y, vertex.z + 1*direction.z)) * gaussD1;
    sum += texture3D(tex, vec3(vertex.x + 2*direction.x, vertex.y + 2*direction.y, vertex.z + 2*direction.z)) * gaussD2;
    sum += texture3D(tex, vec3(vertex.x + 3*direction.x, vertex.y + 3*direction.y, vertex.z + 3*direction.z)) * gaussD3;

    gl_FragColor = color * sum;
}