What are the valid types for a WebGL vertex shader attribute?

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The following attribute seems fine:

attribute vec4 coord;

The following attribute complains that an attribute "cannot be bool or int":

attribute int ty;

The following attribute complains of a "syntax error":

attribute uint ty;

These results seem quite arbitrary. I can't find a list of the valid types for vertex shader attributes. What are the rules for whether an attribute type is valid in WebGL?

vertex-shader webgl opengl-es
1 Answers

OpenGL ES Shading Language 1.00 specification, page 36, section 4.3.3: "Attribute":

The attribute qualifier is used to declare variables that are passed to a vertex shader from OpenGL ES on a per-vertex basis. It is an error to declare an attribute variable in any type of shader other than a vertex shader. Attribute variables are read-only as far as the vertex shader is concerned. Values for attribute variables are passed to a vertex shader through the OpenGL ES vertex API or as part of a vertex array. They convey vertex attributes to the vertex shader and are expected to change on every vertex shader run. The attribute qualifier can be used only with the data types float, vec2, vec3, vec4, mat2, mat3, and mat4. Attribute variables cannot be declared as arrays or structures.

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