const float RING_STRENGTH   = 0.0000;
const float RING_BLUR       = 0.0030;
const float MARKER_STRENGTH = 0.0000;
const float MARKER_BLUR     = 0.0030;
const vec2  VEC_HORZ        = vec2(1.0, 0.0);
const float PI              = 3.1415926535897932384626433832795;

/**
 * Calculate the a double ended smoothstep
 *
 * b0  --> b1  --> b2  --> b3
 * 0.0     1.0     1.0     0.0
 */
float smoothstep2(float b0, float b1, float b2, float b3, float v) {
    return smoothstep(b0, b1, v) * (1.0 - smoothstep(b2, b3, v));
}

/**
 * Calculate a line (vertical or horizonal)
 *
 * @param actual    The current value of the fragment
 * @param expected  The expected value of the fragment
 * @param strength  The strength of the line
 * @param blur      Blur value of the line at the borders
 */
float calcLine(float actual, float expected, float strength, float blur) {
    return smoothstep2(
        expected - strength - blur,
        expected - strength,
        expected + strength,
        expected + strength + blur,
        actual);
}

/**
 * Calculate the angle between the two passed vectors
 */
float calcAngle(vec2 v1, vec2 v2) {
    v1 = -v1;
    return -atan(
        v1.x * v2.y - v1.y * v2.x,
        v1.x * v2.x + v1.y * v2.y);
}

/**
 * Calculate pseudo random value
 */
float random(float seed) {
    return fract(sin(dot(vec4(seed), vec4(12.9898, 78.233, 45.164, 53.1324))) * 43758.5453);
}

/**
 * Linear animation
 *
 * @param v0    Start value
 * @param v1    End value
 * @param t     Time in range of 0.0 to 1.0
 */
float animLinear(float v0, float v1, float t) {
    return v0 + t * (v1 - v0);
}

/**
 * Quadric ease in ease out animation
 *
 * @param v0    Start value
 * @param v1    End value
 * @param t     Time in range of 0.0 to 1.0
 */
float animEaseInOutQuadric(float v0, float v1, float t) {
    float x = t * t * (3.0 - 2.0 * t);

    return v0 + x * (v1 - v0);
}

/**
 * Calculate the position of the marker
 *
 * @param t     Animation progress in range 0.0 to 1.0
 * @param a     Angle of the current fragment
 * @param r     Radius of the current fragment
 * @param zoom  Current zoom value
 */
float calcMarker(float t, float a, float r, float zoom) {
    float m = calcAngle(uMarker, VEC_HORZ);
    m = calcLine(a, m, MARKER_STRENGTH / r / zoom, MARKER_BLUR / r / zoom);
    m *= smoothstep2(
        t * (uRings[0] - 0.25),
        t *  uRings[0],
        t *  uRings[1],
        t * (uRings[1] + 0.10),
        r);
    m *= 0.75;

    return m;
}

/**
 * Calculate the animation value of a ring
 *
 * @param t         Animation progress in range 0.0 to 1.0
 * @param a         Angle of the current fragment
 * @param overfill  Overfilling the ring by the given value
 */
float calcRingsAnimation(float t, float a, float overfill) {
    float t_opn_ring = clamp((t - 0.25) / 0.75, 0.0, 1.0);

    float f = a / PI + 1.0;
    f = f * 2.0;
    f = fract(f + 0.5);
    f = smoothstep2(
        animLinear(0.4, 0.0 - overfill, t_opn_ring),
        animLinear(0.5, 0.1 - overfill, t_opn_ring),
        animLinear(0.5, 0.9 + overfill, t_opn_ring),
        animLinear(0.6, 1.0 + overfill, t_opn_ring),
        f);

    return f;
}

/**
 * Calculate the value of an ring
 *
 * @param t         Animation progress in range 0.0 to 1.0
 * @param anim      Animation value calculated by 'calcRingsAnimation'
 * @param ring      Value / position of the ring
 * @param r         Radius of the current fragment
 * @param zoom      Current zoom value
 */
float calcRing(float t, float anim, float ring, float r, float zoom) {
    return anim * calcLine(r, animEaseInOutQuadric(uSize, ring, t), RING_STRENGTH / zoom, RING_BLUR / zoom);
}

/**
 * Calculate the alpha value of the whole rendered primitive
 *
 * @param t_opn     Progress of the start animation in the range of 0.0 to 1.0
 * @param t_cls     Progress of the close animation in the range of 0.0 to 1.0
 */
float calcAlpha(float t_opn, float t_cls) {
    float as = (0.5 + 0.5 * step(1.0 - t_opn, random(uProgress)));
    float ae = (0.5 + 0.5 * step(      t_cls, random(uProgress))) * (1.0 - t_cls);

    return as * ae;
}