glVertexAttrib
3G

# glVertexAttrib

Specifies the value of a generic vertex attribute

## C Specification

    		void glVertexAttrib1f
    		GLuint index
    		GLfloat v0

    		void glVertexAttrib1s
    		GLuint index
    		GLshort v0

    		void glVertexAttrib1d
    		GLuint index
    		GLdouble v0

    		void glVertexAttrib2f
    		GLuint index
    		GLfloat v0
    		GLfloat v1

    		void glVertexAttrib2s
    		GLuint index
    		GLshort v0
    		GLshort v1

    		void glVertexAttrib2d
    		GLuint index
    		GLdouble v0
    		GLdouble v1

    		void glVertexAttrib3f
    		GLuint index
    		GLfloat v0
    		GLfloat v1
    		GLfloat v2

    		void glVertexAttrib3s
    		GLuint index
    		GLshort v0
    		GLshort v1
    		GLshort v2

    		void glVertexAttrib3d
    		GLuint index
    		GLdouble v0
    		GLdouble v1
    		GLdouble v2

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

    		void glVertexAttrib4s
    		GLuint index
    		GLshort v0
    		GLshort v1
    		GLshort v2
    		GLshort v3

    		void glVertexAttrib4d
    		GLuint index
    		GLdouble v0
    		GLdouble v1
    		GLdouble v2
    		GLdouble v3

    		void glVertexAttrib4Nub
    		GLuint index
    		GLubyte v0
    		GLubyte v1
    		GLubyte v2
    		GLubyte 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 glVertexAttrib1sv
    		GLuint index
    		const GLshort *v

    		void glVertexAttrib1dv
    		GLuint index
    		const GLdouble *v

    		void glVertexAttrib2fv
    		GLuint index
    		const GLfloat *v

    		void glVertexAttrib2sv
    		GLuint index
    		const GLshort *v

    		void glVertexAttrib2dv
    		GLuint index
    		const GLdouble *v

    		void glVertexAttrib3fv
    		GLuint index
    		const GLfloat *v

    		void glVertexAttrib3sv
    		GLuint index
    		const GLshort *v

    		void glVertexAttrib3dv
    		GLuint index
    		const GLdouble *v

    		void glVertexAttrib4fv
    		GLuint index
    		const GLfloat *v

    		void glVertexAttrib4sv
    		GLuint index
    		const GLshort *v

    		void glVertexAttrib4dv
    		GLuint index
    		const GLdouble *v

    		void glVertexAttrib4iv
    		GLuint index
    		const GLint *v

    		void glVertexAttrib4bv
    		GLuint index
    		const GLbyte *v

    		void glVertexAttrib4ubv
    		GLuint index
    		const GLubyte *v

    		void glVertexAttrib4usv
    		GLuint index
    		const GLushort *v

    		void glVertexAttrib4uiv
    		GLuint index
    		const GLuint *v

    		void glVertexAttrib4Nbv
    		GLuint index
    		const GLbyte *v

    		void glVertexAttrib4Nsv
    		GLuint index
    		const GLshort *v

    		void glVertexAttrib4Niv
    		GLuint index
    		const GLint *v

    		void glVertexAttrib4Nubv
    		GLuint index
    		const GLubyte *v

    		void glVertexAttrib4Nusv
    		GLuint index
    		const GLushort *v

    		void glVertexAttrib4Nuiv
    		GLuint index
    		const GLuint *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

OpenGL defines a number of standard vertex attributes that applications can modify with standard API entry points (color, normal, texture coordinates, etc.). 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 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 letters `s`, `f`, `i`, `d`, `ub`, `us`, and `ui` indicate whether the arguments are of type short, float, int, double, unsigned byte, unsigned short, or unsigned int. When `v` is appended to the name, the commands can take a pointer to an array of such values. The commands containing `N` indicate that the arguments will be passed as fixed-point values that are scaled to a normalized range according to the component conversion rules defined by the OpenGL specification. Signed values are understood to represent fixed-point values in the range [-1,1], and unsigned values are understood to represent fixed-point values in the range [0,1].

OpenGL 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 more 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, just like standard vertex attributes, 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.

The generic vertex attribute with index 0 is the same as the vertex position attribute previously defined by OpenGL. A glVertex2, glVertex3, or glVertex4 command is completely equivalent to the corresponding `glVertexAttrib` command with an index argument of 0. A vertex shader can access generic vertex attribute 0 by using the built-in attribute variable `gl_Vertex`. There are no current values for generic vertex attribute 0. This is the only generic vertex attribute with this property; calls to set other standard vertex attributes can be freely mixed with calls to set any of the other generic vertex attributes.

## Notes

`glVertexAttrib` is available only if the GL version is 2.0 or greater.

Generic vertex attributes can be updated at any time. In particular, `glVertexAttrib` can be called between a call to glBegin and the corresponding call to glEnd.

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.

There is no provision for binding standard vertex attributes; therefore, it is not possible to alias generic attributes with standard attributes.

## 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, glVertex, 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/.