Why is GL_ALIASED_POINT_SIZE different between WebGL and Cocoa?

Question

My WebGL's ALIASED_POINT_SIZE (in Safari and Chrome) is 33901.

On the other hand, in my native OpenGL (on Mac/Cocoa), it is just (1,64).

Why are the two values different? And is there no way to increase gl_PointSize ?

Answer 1

You are looking at two different values:

• 33901 (or 0x846d in hex) is the value of GL_ALIASED_POINT_SIZE_RANGE , which is an enum value used to query the point size range.
• (1, 64) must be a point size range you already queried.

In native OpenGL, you would query the point size range with:

GLint range[2];
glGetIntegerv(GL_ALIASED_POINT_SIZE_RANGE, range);

I haven't used WebGL, but based on the documentation the corresponding call there should be:

gl.getParameter(gl.ALIASED_POINT_SIZE_RANGE)

Answer 2

gl_PointSize is a global you set in your vertex shader to set the size of the next point to be rasterized. You can set it anyway you please, from a constant (all points will be the same size), from a uniform (all points will be the same size that you can set at runtime), from an attribute (every point will be a different size depending on the per point data you supply), from some equation, etc (every point will be a different size depending on your equation).

ALIASED_POINT_SIZE_RANGE is a constant value you pass to glGetIntegerv in OpenGL and gl.getParameter in WebGL that returns the range of point sizes your GPU/Driver supports.

Note that WebGL and OpenGL ES 2.0 only require a max point size of 1.0. That means if you count on points be able to render larger than 1 pixel you'll need to find some other solution on certain hardware. You can see the supported sizes near the bottom of this page .