Max number of textures in WebGL?

Question

I know that there is a limit of 8 textures in WebGL.

My question is that, is 8 the limit globally, or per shader/program wise?

If it's per shader/program wise limit, does that mean, once I load the textures to uniforms of one shader, I can start reusing these slots for other shaders? Say I used TEXTURE0 for one shape, can I use TEXTURE0 in another shape?

Answer 1

The limit is per draw call. When you make a draw call, and invoke a particular shader program, you are constrained by the limit, but your next draw call can use completely different textures in the same animation frame.

Also, 8 is just the minimum guarantee. Systems are required to support at least eight to be considered WebGL conformant. But nicer graphics cards support more than eight. You can query the max number of image textures for the platform you're on like this:

var maxTextures = gl.getParameter(gl.MAX_TEXTURE_IMAGE_UNITS);

You can also look for vertex textures:

gl.getParameter(gl.MAX_VERTEX_TEXTURE_IMAGE_UNITS)

Or a combination of the two:

gl.getParameter(gl.MAX_COMBINED_TEXTURE_IMAGE_UNITS)

You can also use a site like WebGL Report (Disclaimer, I'm a contributor) to look up this stat for the platform you're on (under Fragment Shader -> Max Texture Units).

EDIT: When this answer was first written, there was another useful site called "WebGL Stats" that would show aggregate data for WebGL support in a variety of browsers. Sadly, that site disappeared a couple years ago without warning. But even back then, most devices supported at least 16 textures.