// Starfield Generator
// HMS MediaEngine – Generator (GLES, Raspberry Pi). ES 2.0: texture2D, gl_FragColor, Schleifen mit konstanter Höchstgrenze.
#version 100
precision mediump float;

uniform vec2  u_resolution;
uniform float u_time_seconds;
uniform float u_delta_seconds;
uniform float u_frame_index;
uniform float u_layer_opacity;
uniform float u_audio_rms;
uniform float u_audio_peak;
uniform float u_audio_bass;
uniform float u_audio_mid;
uniform float u_audio_treble;
uniform float u_audio_beat;
uniform float4 param_color_a;
uniform float4 param_color_b;
uniform float param_count;
uniform float param_size;
uniform float param_speed;
uniform float param_direction_x;
uniform float param_direction_y;
uniform float param_depth;
uniform float param_twinkle;
uniform float param_seed;
uniform float u_quality_samples;

varying vec2 v_uv;

float hash21(vec2 p)
{
    p = fract(p * vec2(123.34, 456.21));
    p += dot(p, p + 45.32);
    return fract(p.x * p.y);
}

void main()
{
    vec2 p = v_uv;
    float t = u_time_seconds * param_speed;
    float maxN = clamp(u_quality_samples, 1.0, 512.0);
    float dl = length(vec2(param_direction_x, param_direction_y));
    vec2 dir = dl > 1e-4 ? vec2(param_direction_x, param_direction_y) / dl : vec2(0.0, -1.0);
    float acc = 0.0;
    float colAcc = 0.0;
    for (int i = 0; i < 512; i++)
    {
        if (float(i) >= maxN) { break; }
        vec2 base = vec2(hash21(vec2(float(i) + param_seed, 1.0)), hash21(vec2(float(i) + param_seed, 2.0)));
        float depth = hash21(vec2(float(i) + param_seed, 3.0)) * param_depth;
        vec2 pos = base + dir * t * (0.1 + depth * 0.9);
        pos = fract(pos);
        vec2 d = pos - p;
        d = abs(d);
        d = min(d, 1.0 - d);
        float dist = length(d);
        float s = param_size * (0.3 + depth);
        float star = exp(-dist * dist / max(s * s, 1e-5));
        float tw = 0.5 + 0.5 * sin(t * 3.0 + param_seed * 10.0 + float(i) * 1.7);
        star *= mix(1.0, tw, param_twinkle);
        acc += star;
        colAcc += star * depth;
    }
    acc = clamp(acc, 0.0, 1.0);
    float mixT = maxN > 1.0 ? colAcc / max(acc, 1e-5) : 0.0;
    vec3 col = mix(param_color_a.rgb, param_color_b.rgb, mixT);
    gl_FragColor = vec4(col * acc * u_layer_opacity, acc * u_layer_opacity);
}