gl_PointSize zero in WebGL

Question

I have a vertex shader that sets gl_PointSize = mix( 0. , 5. , step(foo,bar) );. My mac with an Intel HD Graphics 5000, renders only the points that are 5, not the 0. Another mac with some kind of a radeon rendered the zeroes as if they were one.

I've read through the gl_PointSize and did not understand what is the desired behavior with gl_PointSize = 0.; and did not understand the bit about aliasing and rounding.

If I want to "hide" certain points, should I rely on gl_PointSize = 0.; to not even rasterize the points, or should i use something else?

Two things come to mind:

//frag

...
if( vSomeVarying < 0.5 ) discard; //but why even rasterize, and this is still like rendering all the points regardless of the discard?
...


//vert

if( someValue < 0.5 ){

  gl_Position.z = 2.; //should clip it?

}

Answer 1

If I want to "hide" certain points, should I rely on gl_PointSize = 0.; to not even rasterize the points, or should i use something else?

Use something else, because in GLES 2.0.25 on p51:

If the value written to gl_PointSize is less than or equal to zero, results are undefined.

Forcing the vert to be clipped works.