glVertexAttrib
3G

# glVertexAttrib

specify the value of a generic vertex attribute

## C Specification

    		void glVertexAttrib1f
    		GLuint index
    		GLfloat v0

    		void glVertexAttrib2f
    		GLuint index
    		GLfloat v0
    		GLfloat v1

    		void glVertexAttrib3f
    		GLuint index
    		GLfloat v0
    		GLfloat v1
    		GLfloat v2

    		void glVertexAttrib4f
    		GLuint index
    		GLfloat v0
    		GLfloat v1
    		GLfloat v2
    		GLfloat v3

## Parameters

`index`

  Specifies the index of the generic vertex attribute to be modified.

`v0`, `v1`, `v2`, `v3`

  Specifies the new values to be used for the specified vertex attribute.

## C Specification

    		void glVertexAttrib1fv
    		GLuint index
    		const GLfloat *v

    		void glVertexAttrib2fv
    		GLuint index
    		const GLfloat *v

    		void glVertexAttrib3fv
    		GLuint index
    		const GLfloat *v

    		void glVertexAttrib4fv
    		GLuint index
    		const GLfloat *v

## Parameters

`index`

  Specifies the index of the generic vertex attribute to be modified.

`v`

  Specifies a pointer to an array of values to be used for the generic vertex attribute.

## Description

The `glVertexAttrib` family of entry points allows an application to pass generic vertex attributes in numbered locations.

Generic attributes are defined as four-component values that are organized into an array. The first entry of this array is numbered 0, and the size of the array is specified by the implementation-dependent symbolic constant `GL_MAX_VERTEX_ATTRIBS`. Individual elements of this array can be modified with a `glVertexAttrib` call that specifies the index of the element to be modified and a value for that element.

These commands can be used to specify one, two, three, or all four components of the generic vertex attribute specified by `index`. A `1` in the name of the command indicates that only one value is passed, and it will be used to modify the first component of the generic vertex attribute. The second and third components will be set to 0, and the fourth component will be set to 1. Similarly, a `2` in the name of the command indicates that values are provided for the first two components, the third component will be set to 0, and the fourth component will be set to 1. A `3` in the name of the command indicates that values are provided for the first three components and the fourth component will be set to 1, whereas a `4` in the name indicates that values are provided for all four components.

The letter `f` indicates that the arguments are of type float. When `v` is appended to the name, the commands can take a pointer to an array of floats.

OpenGL ES Shading Language attribute variables are allowed to be of type mat2, mat3, or mat4. Attributes of these types may be loaded using the `glVertexAttrib` entry points. Matrices must be loaded into successive generic attribute slots in column major order, with one column of the matrix in each generic attribute slot.

A user-defined attribute variable declared in a vertex shader can be bound to a generic attribute index by calling glBindAttribLocation. This allows an application to use descriptive variable names in a vertex shader. A subsequent change to the specified generic vertex attribute will be immediately reflected as a change to the corresponding attribute variable in the vertex shader.

The binding between a generic vertex attribute index and a user-defined attribute variable in a vertex shader is part of the state of a program object, but the current value of the generic vertex attribute is not. The value of each generic vertex attribute is part of current state and it is maintained even if a different program object is used.

An application may freely modify generic vertex attributes that are not bound to a named vertex shader attribute variable. These values are simply maintained as part of current state and will not be accessed by the vertex shader. If a generic vertex attribute bound to an attribute variable in a vertex shader is not updated while the vertex shader is executing, the vertex shader will repeatedly use the current value for the generic vertex attribute.

## Notes

It is possible for an application to bind more than one attribute name to the same generic vertex attribute index. This is referred to as aliasing, and it is allowed only if just one of the aliased attribute variables is active in the vertex shader, or if no path through the vertex shader consumes more than one of the attributes aliased to the same location. OpenGL implementations are not required to do error checking to detect aliasing, they are allowed to assume that aliasing will not occur, and they are allowed to employ optimizations that work only in the absence of aliasing.

## Errors

`GL_INVALID_VALUE` is generated if `index` is greater than or equal to `GL_MAX_VERTEX_ATTRIBS`.

## Associated Gets

glGet with the argument `GL_CURRENT_PROGRAM`

glGetActiveAttrib with argument `program` and the index of an active attribute variable

glGetAttribLocation with argument `program` and an attribute variable name

glGetVertexAttrib with arguments `GL_CURRENT_VERTEX_ATTRIB` and `index`

## See Also

glBindAttribLocation, glVertexAttribPointer

## Copyright

Copyright 2003-2005 3Dlabs Inc. Ltd. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.