#version 450 core

#pragma include ./tail_render_shared.glsl
#pragma include ../misc/camera.glsl

/*
Vertex Layout:
        .-- 0 --- 3 --- 6 --- 9  --- 12 --- 15
       /    |  \  |  \  |  \  |   \  |   \  |
 SHIP ----- 1 --- 4 --- 7 --- 10 --- 13 --- 16
       \    |  /  |  /  |  /  |   /  |   /  |
        `-- 2 --- 5 --- 8 --- 11 --- 14 --- 17
*/

in VertexData vertexData[];

layout (points) in;
layout (triangle_strip, max_vertices = 24) out;

out FragmentData fragmentData;

struct Vertex {
    vec2 pos;
    vec4 clr;
};

vec2 ortho2(vec2 pos, vec2 ref) {
    vec2 dir = normalize(pos - ref);

    return vec2(dir.y, -dir.x);
}

vec2 ortho3(vec2 ref0, vec2 pos, vec2 ref1) {
    vec2 dir0 = ortho2(ref0, pos);
    vec2 dir1 = ortho2(pos, ref1);

    return normalize(dir0 + dir1);
}

void emit(Vertex v) {
    gl_Position         = uCamera.projection * uCamera.view * vec4(v.pos, 0.0, 1.0);
    fragmentData.color  = v.clr;

    EmitVertex();
}

void main() {
    VertexData d = vertexData[0];

    vec2 ortho;
    Vertex vertices[18];

    /* tail[0] */

    ortho = ortho2(d.tail[0], d.tail[1]);

    vertices[0].pos = d.tail[0] + TAIL_WIDTH * ortho;
    vertices[0].clr = vec4(d.color, 0.8 * TAIL_ALPHA);

    vertices[1].pos = d.tail[0];
    vertices[1].clr = vec4(d.color, 1.0 * TAIL_ALPHA);

    vertices[2].pos = d.tail[0] - TAIL_WIDTH * ortho;
    vertices[2].clr = vec4(d.color, 0.8 * TAIL_ALPHA);

    /* tail[1] */

    ortho = ortho3(d.tail[0], d.tail[1], d.tail[2]);

    vertices[3].pos = d.tail[1] + TAIL_WIDTH * ortho;
    vertices[3].clr = vec4(d.color, 0.6 * TAIL_ALPHA);

    vertices[4].pos = d.tail[1];
    vertices[4].clr = vec4(d.color, 0.8 * TAIL_ALPHA);

    vertices[5].pos = d.tail[1] - TAIL_WIDTH * ortho;
    vertices[5].clr = vec4(d.color, 0.6 * TAIL_ALPHA);

    /* tail[2] */

    ortho = ortho3(d.tail[1], d.tail[2], d.tail[3]);

    vertices[6].pos = d.tail[2] + TAIL_WIDTH * ortho;
    vertices[6].clr = vec4(d.color, 0.4 * TAIL_ALPHA);

    vertices[7].pos = d.tail[2];
    vertices[7].clr = vec4(d.color, 0.6 * TAIL_ALPHA);

    vertices[8].pos = d.tail[2] - TAIL_WIDTH * ortho;
    vertices[8].clr = vec4(d.color, 0.4 * TAIL_ALPHA);

    /* tail[3] */

    ortho = ortho3(d.tail[2], d.tail[3], d.tail[4]);

    vertices[9].pos = d.tail[3] + TAIL_WIDTH * ortho;
    vertices[9].clr = vec4(d.color, 0.2 * TAIL_ALPHA);

    vertices[10].pos = d.tail[3];
    vertices[10].clr = vec4(d.color, 0.4 * TAIL_ALPHA);

    vertices[11].pos = d.tail[3] - TAIL_WIDTH * ortho;
    vertices[11].clr = vec4(d.color, 0.2 * TAIL_ALPHA);

    /* tail[4] */

    ortho = ortho3(d.tail[3], d.tail[4], d.tail[5]);

    vertices[12].pos = d.tail[4] + TAIL_WIDTH * ortho;
    vertices[12].clr = vec4(d.color, 0.0 * TAIL_ALPHA);

    vertices[13].pos = d.tail[4];
    vertices[13].clr = vec4(d.color, 0.2 * TAIL_ALPHA);

    vertices[14].pos = d.tail[4] - TAIL_WIDTH * ortho;
    vertices[14].clr = vec4(d.color, 0.0 * TAIL_ALPHA);

    /* tail[5] */

    ortho = ortho2(d.tail[4], d.tail[5]);

    vertices[15].pos = d.tail[5] + TAIL_WIDTH * ortho;
    vertices[15].clr = vec4(d.color, 0.0 * TAIL_ALPHA);

    vertices[16].pos = d.tail[5];
    vertices[16].clr = vec4(d.color, 0.0 * TAIL_ALPHA);

    vertices[17].pos = d.tail[5] - TAIL_WIDTH * ortho;
    vertices[17].clr = vec4(d.color, 0.0 * TAIL_ALPHA);

    /* emit */

    emit(vertices[1]);
    emit(vertices[0]);
    emit(vertices[4]);
    emit(vertices[3]);
    emit(vertices[7]);
    emit(vertices[6]);
    emit(vertices[10]);
    emit(vertices[9]);
    emit(vertices[13]);
    emit(vertices[12]);
    emit(vertices[16]);
    emit(vertices[15]);
    EndPrimitive();

    emit(vertices[1]);
    emit(vertices[2]);
    emit(vertices[4]);
    emit(vertices[5]);
    emit(vertices[7]);
    emit(vertices[8]);
    emit(vertices[10]);
    emit(vertices[11]);
    emit(vertices[13]);
    emit(vertices[14]);
    emit(vertices[16]);
    emit(vertices[17]);
    EndPrimitive();
}