CODEWITHSUNDEEP
webgl
duhaime
duhaime

Reputation: 27574

WebGL: Are there cases where gl.MAX_TEXTURE_IMAGE_UNITS == 1

Sorry to ask such a strange question, but I'm working on some logic for a WebGL visualization and would like to know, are there cases where:

gl.getParameter(gl.MAX_TEXTURE_IMAGE_UNITS)

equals 1?

I ask because I'm trying to figure out how many vertices I can draw in each draw call, and each vertex needs some content from one of several textures. The minimal case I'm wanting to support is one in which I load two textures for each draw call, but if there are cards that don't support multiple textures per draw call I'll need to rethink my life.

Upvotes: 1

Views: 998

Answers (1)

user128511
user128511

Reputation:

The minimum value for MAX_TEXTURE_IMAGE_UNITS WebGL is required to support is 8. You can look up the limits in the spec section 6.2. Note: Search for "MAX TEXTURE IMAGE UNITS" (with the spaces not underscores)

That said WebGL has a different limit for textures used in a fragment shader vs textures used in a vertex shader.

For a vertex shader the minimum requires is 0 on WebGL1. You can check the number of textures supported in a vertex shader by looking at MAX_VERTEX_TEXTURE_IMAGE_UNITS.

Fortunately most machines support at least 4 in the vertex shader

There is also yet another limit MAX_COMBINED_TEXTURE_IMAGE_UNITS which is how many textures total you can use combined. In other words if MAX_COMBINED_TEXTURE_IMAGE_UNITS is 8, MAX_VERTEX_TEXTURE_IMAGE_UNITS is 8 and MAX_VERTEX_TEXTURE_IMAGE_UNITS is 4 that means you could use 8 textures at once of which up to 4 could be used in the vertex shader. You could not use 12 textures at once.

Other minimums

MAX VERTEX ATTRIBS               8
MAX VERTEX UNIFORM VECTORS       128
MAX VARYING VECTORS              8
MAX COMBINED TEXTURE IMAGE UNITS 8
MAX VERTEX TEXTURE IMAGE UNITS   0
MAX TEXTURE IMAGE UNITS          8
MAX FRAGMENT UNIFORM VECTORS     16

Upvotes: 2

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