#version 450 core
#include "common.glsl"
// Premultiplied output: glows and fire write alpha 0 (pure additive), sparks
// and smoke write coverage (alpha-blended). Blend func is ONE, ONE_MINUS_SRC_ALPHA.

in vec2 vUV;
in vec4 vColor;
flat in int vKind;
in vec2 vLifeSeed;

layout(location = 0) out vec4 fragColor;

void main() {
    vec2 p = vUV * 2.0 - 1.0;
    float r = length(p);
    float life = vLifeSeed.x, seed = vLifeSeed.y;

    if (vKind == 2) {  // spark / droplet
        float a = (1.0 - smoothstep(0.6, 1.0, r)) * vColor.a;
        fragColor = vec4(vColor.rgb * a, a);
        return;
    }
    if (vKind == 3) {
        // Flame lick: a soft-topped blob with a crisp, noise-eroded silhouette,
        // shaded from a hot yellow center to orange and a red rim; it reddens
        // and erodes as it rises. Nearly opaque (HD-2D fires read as solid,
        // painterly shapes), emissive HDR so the core blooms.
        float taper = 1.0 + 0.45 * (p.y * 0.5 + 0.5);
        float d = length(vec2(p.x * taper, p.y * 0.8 + 0.1));
        vec2 q = vec2(p.x * 1.8, p.y * 1.5 - uTime * 2.6) + seed * 37.0;
        float n = vnoise(q) * 0.7 + vnoise(q * 2.4 + 11.0) * 0.3;
        float e = d + (n - 0.5) * (0.35 + 0.7 * life);
        float body = 1.0 - smoothstep(0.62, 0.76, e);
        if (body <= 0.0) discard;
        // Young licks stay hot right to their rim so the mass merges into one
        // bright body; only older, higher licks get the red edge.
        float heat = clamp((1.0 - e / 0.72) * 1.35 + 0.25 * (1.0 - life), 0.0, 1.0) * (1.0 - 0.65 * life);
        vec3 red = vec3(0.8, 0.1, 0.02), orange = vec3(1.8, 0.5, 0.06), yellow = vec3(2.3, 1.4, 0.32);
        vec3 c = heat < 0.5 ? mix(red, orange, heat * 2.0) : mix(orange, yellow, heat * 2.0 - 1.0);
        float a = body * vColor.a;
        fragColor = vec4(c * vColor.rgb * a, a * 0.92);
        return;
    }
    if (vKind == 4) {  // ember
        float core = exp(-r * r * 10.0);
        fragColor = vec4(vColor.rgb * vColor.a * core, 0.0);
        return;
    }
    if (vKind == 5) {  // smoke puff
        vec2 q = p * 1.6 + seed * 23.0 + vec2(0.0, -uTime * 0.3);
        float n = vnoise(q) * 0.6 + vnoise(q * 2.1 + 5.0) * 0.4;
        float a = (1.0 - smoothstep(0.2, 1.0, r + (n - 0.5) * 0.7)) * vColor.a;
        fragColor = vec4(vColor.rgb * a, a);
        return;
    }
    if (vKind == 6) {  // fire glow halo
        float g = exp(-r * r * 3.5) - 0.03;
        fragColor = vec4(vColor.rgb * max(g, 0.0), 0.0);
        return;
    }
    float core = 1.0 - smoothstep(0.0, 0.2, r);
    float halo = exp(-r * r * 9.0) * 0.45;
    fragColor = vec4(vColor.rgb * vColor.a * (core * 1.5 + halo), 0.0);
}