Funny Shader

#version 330 core

layout (points) in;
layout (triangle_strip, max_vertices = 6) out;

uniform float rotation;

const float PI = 3.14159265359;
const float scale = 0.5f;

void emitVertex(vec2 vert){
    gl_Position = vec4(vert, 0, 1f);
    EmitVertex();
}

void createArrow(vec2 mid, int reflect, float rotation, vec2 translation, float scale){
    mat2 m;

    if(reflect == 1){
        m = mat2(-1, 0, 0, 1);
    }
    else{
        m = mat2(1, 0, 0, 1);
    }

    m = m * mat2(cos(rotation), sin(rotation), -sin(rotation), cos(rotation));
    translation = translation * mat2(cos(rotation), sin(rotation), -sin(rotation), cos(rotation));

    emitVertex(translation + mid * m * scale);
    emitVertex(translation + (mid + vec2(0.1f, -0.1f)) * m * scale);
    emitVertex(translation + (mid + vec2(0f, 0.4f)) * m * scale);
}

void createArrow(vec2 mid, float rotation, vec2 translation, float scale) {
    createArrow(mid, 0, rotation, translation, scale);
    createArrow(mid, 1, rotation, translation, scale);
}

void main(){
    vec2 mid = gl_in[0].gl_Position.xy;

    createArrow(mid + vec2(0f, 1f), rotation, vec2(0f, 0f), scale);

    EndPrimitive();
}