2010 Khronos Group
glTransformFeedbackVaryings 3G
glTransformFeedbackVaryings specify values to record in transform feedback buffers

## C Specification

void `glTransformFeedbackVaryings` GLuintprogram GLsizeicount const char **varyings GLenumbufferMode

## Parameters

program

  The name of the target program object.

count

  The number of varying variables used for transform feedback.

varyings

  An array of count zero-terminated strings specifying the names of the varying variables to use for transform feedback.

bufferMode

  Identifies the mode used to capture the varying variables when transform feedback is active. bufferMode must be `GL_INTERLEAVED_ATTRIBS` or `GL_SEPARATE_ATTRIBS`.

## Description

The names of the vertex or geometry shader outputs to be recorded in transform feedback mode are specified using `glTransformFeedbackVaryings`. When a geometry shader is active, transform feedback records the values of selected geometry shader output variables from the emitted vertices. Otherwise, the values of the selected vertex shader outputs are recorded.

The state set by `glTranformFeedbackVaryings` is stored and takes effect next time glLinkProgram is called on program. When glLinkProgram is called, program is linked so that the values of the specified varying variables for the vertices of each primitive generated by the GL are written to a single buffer object if bufferMode is `GL_INTERLEAVED_ATTRIBS` or multiple buffer objects if bufferMode is `GL_SEPARATE_ATTRIBS`.

In addition to the errors generated by `glTransformFeedbackVaryings`, the program program will fail to link if:

- The count specified by `glTransformFeedbackVaryings` is non-zero, but the program object has no vertex or geometry shader.

- Any variable name specified in the varyings array is not declared as an output in the vertex shader (or the geometry shader, if active).

- Any two entries in the varyings array specify the same varying variable.

- The total number of components to capture in any varying variable in varyings is greater than the constant `GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_COMPONENTS` and the buffer mode is `GL_SEPARATE_ATTRIBS`.

- The total number of components to capture is greater than the constant `GL_MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS` and the buffer mode is `GL_INTERLEAVED_ATTRIBS`.

## Notes

`glGetTransformFeedbackVarying` is available only if the GL version is 3.0 or greater.

## Errors

`GL_INVALID_VALUE` is generated if program is not the name of a program object.

`GL_INVALID_VALUE` is generated if bufferMode is `GL_SEPARATE_ATTRIBS` and count is greater than the implementation-dependent limit `GL_MAX_TRANSFORM_FEEDBACK_SEPARATE_ATTRIBS`.

## Associated Gets

glGetTransformFeedbackVarying

## See Also

glBeginTransformFeedback, glEndTransformFeedback, glGetTransformFeedbackVarying

## Copyright

Copyright 2010 Khronos Group. 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/.