ot(u_transform[0], u_transform[0]),
                     dot(u_transform[1], u_transform[1]));
   vec2 invScale = u_aa * inversesqrt(scale + 1.0e-6);
   scale *= invScale;
   vec2 extrude = a_vertex.xy +
                  invScale * (2.0 * a_vertex.xy - 1.0);
   vec2 vertex = u_transform[0] * extrude.x +
                 u_transform[1] * extrude.y +
                 u_transform[2];
   gl_Position = vec4(vertex * 2.0 / u_viewport - 1.0, 0.0, 1.0);
   v_cliptc = vertex / u_viewport;
   v_clipdist = vec4(vertex - u_clipbounds.xy,
                     u_clipbounds.zw - vertex);
   float noAA = 1.0 - u_aa;
   v_dist = vec4(extrude, 1.0 - extrude) * scale.xyxy + 0.5 + noAA;
   v_alpha = min(a_vertex.z,
                 min(scale.x, 1.0) * min(scale.y, 1.0) + noAA);
}