Frustum :: struct {
    near_top_left: Vector3;
    near_bottom_left: Vector3;
    near_top_right: Vector3;
    near_bottom_right: Vector3;

    far_top_left: Vector3;
    far_bottom_left: Vector3;
    far_top_right: Vector3;
    far_bottom_right: Vector3;
}

get_frustum :: (fov: float, aspect_ratio: float, z_near: float, z_far: float) -> Frustum {
    frustum: Frustum = ---;

    tan_half_fov := tan(DEGREES_TO_RADIANS * fov * 0.5);

    near_z := z_near;
    near_x := near_z * tan_half_fov;
    near_y := near_z * tan_half_fov * aspect_ratio;

    frustum.near_top_left     = .{-near_x, near_y, near_z};
    frustum.near_bottom_left  = .{-near_x, -near_y, near_z};
    frustum.near_top_right    = .{near_x, near_y, near_z};
    frustum.near_bottom_right = .{near_x, -near_y, near_z};

    far_z := z_far;
    far_x := far_z * tan_half_fov;
    far_y := far_z * tan_half_fov * aspect_ratio;

    frustum.far_top_left     = .{-far_x, far_y, far_z};
    frustum.far_bottom_left  = .{-far_x, -far_y, far_z};
    frustum.far_top_right    = .{far_x, far_y, far_z};
    frustum.far_bottom_right = .{far_x, -far_y, far_z};

    return frustum;
}

get_frustum_aabb :: (frustum: Frustum) -> AABB {
    aabb: AABB;
    aabb_add(*aabb, frustum.near_top_left);
    aabb_add(*aabb, frustum.near_bottom_left);
    aabb_add(*aabb, frustum.near_top_right);
    aabb_add(*aabb, frustum.near_bottom_right);

    aabb_add(*aabb, frustum.far_top_left);
    aabb_add(*aabb, frustum.far_bottom_left);
    aabb_add(*aabb, frustum.far_top_right);
    aabb_add(*aabb, frustum.far_bottom_right);

    return aabb;
}

transform :: (frustum: Frustum, matrix: Matrix4) -> Frustum {
    transformed_frustum: Frustum = ---;

    transformed_frustum.near_top_left = transform_position(frustum.near_top_left, matrix);
    transformed_frustum.near_bottom_left = transform_position(frustum.near_bottom_left, matrix);
    transformed_frustum.near_top_right = transform_position(frustum.near_top_right, matrix);
    transformed_frustum.near_bottom_right = transform_position(frustum.near_bottom_right, matrix);

    transformed_frustum.far_top_left = transform_position(frustum.far_top_left, matrix);
    transformed_frustum.far_bottom_left = transform_position(frustum.far_bottom_left, matrix);
    transformed_frustum.far_top_right = transform_position(frustum.far_top_right, matrix);
    transformed_frustum.far_bottom_right = transform_position(frustum.far_bottom_right, matrix);

    return transformed_frustum;
}