2010 Khronos Group
glBeginTransformFeedback 3G
glBeginTransformFeedback start transform feedback operation

## C Specification

void `glBeginTransformFeedback` GLenum primitiveMode

## Parameters

primitiveMode

  Specify the output type of the primitives that will be recorded into the buffer objects that are bound for transform feedback.

## C Specification

void `glEndTransformFeedback` void

## Description

Transform feedback mode captures the values of varying variables written by the vertex shader (or, if active, the geometry shader). Transform feedback is said to be active after a call to `glBeginTransformFeedback` until a subsequent call to glEndTransformFeedback. Transform feedback commands must be paired.

If no geometry shader is present, while transform feedback is active the mode parameter to glDrawArrays must match those specified in the following table:

Transform Feedback primitiveMode | Allowed Render Primitive modes
--- | ---
`GL_POINTS` | `GL_POINTS`
`GL_LINES` | `GL_LINES`, `GL_LINE_LOOP`, `GL_LINE_STRIP`, `GL_LINES_ADJACENCY`, `GL_LINE_STRIP_ADJACENCY`
`GL_TRIANGLES` | `GL_TRIANGLES`, `GL_TRIANGLE_STRIP`, `GL_TRIANGLE_FAN`, `GL_TRIANGLES_ADJACENCY`, `GL_TRIANGLE_STRIP_ADJACENCY`

If a geometry shader is present, the output primitive type from the geometry shader must match those provided in the following table:

Transform Feedback primitiveMode | Allowed Geometry Shader Output Primitive Type
--- | ---
`GL_POINTS` | `points`
`GL_LINES` | `line_strip`
`GL_TRIANGLES` | `triangle_strip`

## Notes

Geometry shaders, and the `GL_TRIANGLES_ADJACENCY`, `GL_TRIANGLE_STRIP_ADJACENCY`, `GL_LINES_ADJACENCY` and `GL_LINE_STRIP_ADJACENCY` primtive modes are available only if the GL version is 3.2 or greater.

## Errors

`GL_INVALID_OPERATION` is generated if `glBeginTransformFeedback` is executed while transform feedback is active.

`GL_INVALID_OPERATION` is generated if `glEndTransformFeedback` is executed while transform feedback is not active.

`GL_INVALID_OPERATION` is generated by glDrawArrays if no geometry shader is present, transform feedback is active and mode is not one of the allowed modes.

`GL_INVALID_OPERATION` is generated by glDrawArrays if a geometry shader is present, transform feedback is active and the output primitive type of the geometry shader does not match the transform feedback primitiveMode.

`GL_INVALID_OPERATION` is generated by `glEndTransformFeedback` if any binding point used in transform feedback mode does not have a buffer object bound.

`GL_INVALID_OPERATION` is generated by `glEndTransformFeedback` if no binding points would be used, either because no program object is active of because the active program object has specified no varying variables to record.

## 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/.