vec2(1.0f, 1.0f)
          );

          vec2 pos = quad[gl_VertexID] + vec2(float(gl_InstanceID), 0.0f);
          pos /= vec2(u_layer_count, 1.0f);
          gl_Position = vec4(pos * 2.0 - 1.0, 0.0, 1.0);
          v_texcoord = vec3(quad[gl_VertexID], gl_InstanceID);
      }