float vertices[] = {
        // posistions          // normals           // texture coords
      -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
       0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  0.0f,
       0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
       0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
      -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  1.0f,
      -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
    }

#version 330 core

in vec3 frag_pos;
in vec3 frag_nor;
in vec2 frag_tex;

out vec4 frag_color;

void main()
{
    vec2 origin = vec2(0.01, 0.01);

    float width =  1.0 - origin.x * 2.0;
    float height = 1.0 - origin.y * 2.0;

    if( (frag_tex.x >= origin.x && frag_tex.x < origin.x + width) &&
        (frag_tex.y >= origin.y && frag_tex.y < origin.y + height) )
    {
        frag_color = vec4(0.0);
    }
    else
    {
        frag_color = vec4(0.0, 1.0, 0.0, 0.0);
    }
}

glDisable(GL_DEPTH_TEST);
glBindVertexArray(vao);
glDrawArrays(GL_TRIANGLES, 0, 6);