uniform vec4 fadeInColor;
uniform vec4 fadeOutColor;
uniform float maximumDistance;
uniform bool repeat;
uniform vec2 fadeDirection;
uniform vec2 time;

float getTime(float t, float coord)
{
    float scalar = 1.0 / maximumDistance;
    float q  = distance(t, coord) * scalar;
    if (repeat)
    {
        float r = distance(t, coord + 1.0) * scalar;
        float s = distance(t, coord - 1.0) * scalar;
        q = min(min(r, s), q);
    }
    return clamp(q, 0.0, 1.0);
}

czm_material czm_getMaterial(czm_materialInput materialInput)
{
    czm_material material = czm_getDefaultMaterial(materialInput);

    vec2 st = materialInput.st;
    float s = getTime(time.x, st.s) * fadeDirection.s;
    float t = getTime(time.y, st.t) * fadeDirection.t;

    float u = length(vec2(s, t));
    vec4 color = mix(fadeInColor, fadeOutColor, u);

    color = czm_gammaCorrect(color);
    material.emission = color.rgb;
    material.alpha = color.a;

    return material;
}