void quad( int a, int b, int c, int d )
{
	colors[Index] = vertex_colors[a]; points[Index] = vertices[a]; tex_coords[Index]=glm::vec2(0,0); Index++;
    colors[Index] = vertex_colors[b]; points[Index] = vertices[b]; tex_coords[Index]=glm::vec2(0,1); Index++;
    colors[Index] = vertex_colors[c]; points[Index] = vertices[c]; tex_coords[Index]=glm::vec2(1,1); Index++;
    colors[Index] = vertex_colors[a]; points[Index] = vertices[a]; tex_coords[Index]=glm::vec2(1,0); Index++;
    colors[Index] = vertex_colors[c]; points[Index] = vertices[c]; tex_coords[Index]=glm::vec2(0,1); Index++;
    colors[Index] = vertex_colors[d]; points[Index] = vertices[d]; tex_coords[Index]=glm::vec2(1,1); Index++;
}