How using gl_PointCoord at fragment shader with QtQuick for points primitive

Question

For example simple fragment shader for circle points:

void main()
{
   float size = 0.5;
   vec2 center = vec2(0.5);
   vec2 d = gl_PointCoord - center;
   float distSquared = dot(d, d);

   if(distSquared < size * size)
       gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
   else
       discard;
}

Here gl_PointCoord always vec2(0.0, 0.0) because it requests glEnable(GL_POINT_SPRITE) but how enable that for QtQuick?