//Fragment shader
#version 420
out vec4 color;
in vec3 o_position;

void main() {
    color = vec4(o_position+0.5, 1.0);
}

// Vertex shader
#version 420
layout(location=0) in vec3 position;
out vec3 o_position;

uniform vec4 rot_quaternion = vec4(1, 0.0, 0.0, 0.0);

vec4 hamilton_product(vec4, vec4);

void main() {
    //rotate by performing the hamilton product of rot_quaternion on position, then performing the hamilton product of the result with rot-quaternion conjugate.
    vec4 rotated = hamilton_product(rot_quaternion, vec4(0, position));
    rotated = hamilton_product(rotated, vec4(rot_quaternion.x, rot_quaternion.yzw*-1));


    float width = 1024.0,
        height = 768.0,
        a_ratio = width/height,
        v_angle = 45,
        scale_fac = 1/tan(radians(v_angle)),
        near = 0.1,
        far = 100.0;

    vec4 pos_4d = vec4(rotated.yz, rotated.w+3, 1);
    mat4 projection = mat4(scale_fac,0,0,0,
                           0,a_ratio*scale_fac,0,0,
                           0,0,1*(near+far)/(far-near),-2*((far*near)/(far-near)),
                           0,0,1,0);
    vec4 final = pos_4d*projection;

    o_position = position;
    gl_Position = vec4(final);
}


vec4 hamilton_product(vec4 q1, vec4 q2){
    return vec4(q1.x*q2.x - q1.y*q2.y - q1.z*q2.z - q1.w*q2.w,
                q1.x*q2.y + q1.y*q2.x + q1.z*q2.w - q1.w*q2.z,
                q1.x*q2.z - q1.y*q2.w + q1.z*q2.x + q1.w*q2.y,
                q1.x*q2.w + q1.y*q2.z - q1.z*q2.y + q1.w*q2.x);

}