glGetTransformFeedback - OpenGL 4 Reference Pages

## Name

glGetTransformFeedbackiv — query the state of a transform feedback object.

## C Specification

`void glGetTransformFeedbackiv(` | GLuint xfb,
| GLenum pname,
| GLint *param`)`;

`void glGetTransformFeedbacki_v(` | GLuint xfb,
| GLenum pname,
| GLuint index,
| GLint *param`)`;

`void glGetTransformFeedbacki64_v(` | GLuint xfb,
| GLenum pname,
| GLuint index,
| GLint64 *param`)`;

## Parameters

`xfb`

  The name of an existing transform feedback object, or zero for the default transform feedback object.

`pname`

  Property to use for the query. Must be one of the values: `GL_TRANSFORM_FEEDBACK_BUFFER_BINDING`, `GL_TRANSFORM_FEEDBACK_BUFFER_START`, `GL_TRANSFORM_FEEDBACK_BUFFER_SIZE`, `GL_TRANSFORM_FEEDBACK_PAUSED`, `GL_TRANSFORM_FEEDBACK_ACTIVE`.

`index`

  Index of the transform feedback stream (for indexed state).

`param`

  The address of a buffer into which will be written the requested state information.

## Description

In order to use the Transform Feedback functionality, you need to configure the Transform Feedback Buffer indexed bindings. This can be achieved by either using `glBindBufferBase` or `glBindBuffersBase` to associate whole buffer object storage to one of the Transform Feedback Binding Points, or by calling `glBindBufferRange` or `glBindBuffersRange` to use a region of a buffer object storage for the binding. You may want to (but are not required to) bind a Transform Feedback Object first, in order to cache the binding configuration. This usually allows you to restore the Transform Feedback configuration faster, than if you were to execute a list of API calls necessary to set up the Transform Feedback state of your liking.

This reference page discusses two types of getters that operate on Transform Feedback Objects and their bindings.

The first class operates on general Transform Feedback binding point and includes `glGetTransformFeedbackiv` function. `glGetTransformFeedbackiv` can be used to retrieve information about Transform Feedback object bound to the general Transform Feedback binding point, as configured with a `glBindTransformFeedback` call. In this case, you can check:

- What the ID of the currently bound Transform Feedback Object is; (`GL_TRANSFORM_FEEDBACK_BUFFER_BINDING`)

- Whether the Transform Feedback process is currently paused; (`GL_TRANSFORM_FEEDBACK_PAUSED`)

- Whether the Transform Feedback process has been begun and is currently undergoing; (`GL_TRANSFORM_FEEDBACK_ACTIVE`)

The latter class, which includes `glGetTransformFeedbacki_v` and `glGetTransformFeedbacki64_v` functions, can be used to check what the current configuration of each of the buffer object regions bound to Transform Feedback Buffer binding points is. This allows you to query for the following information:

- `glGetTransformFeedbacki_v` only: What the ID of the Buffer Object bound to a Transform Feedback Binding Point of user-specified index is; (`GL_TRANSFORM_FEEDBACK_BUFFER_BINDING`).

- `glGetTransformFeedbacki64_v` only: What the start offset configured for the binding is; (`GL_TRANSFORM_FEEDBACK_BUFFER_START`);

- `glGetTransformFeedbacki64_v` only: What the length of the region used for the binding is; (`GL_TRANSFORM_FEEDBACK_BUFFER_SIZE`);

## Errors

`GL_INVALID_OPERATION` error is generated if `xfb` is not zero or the name of an existing transform feedback object.

`GL_INVALID_ENUM` error is generated by `glGetTransformFeedbackiv` if `pname` is not `GL_TRANSFORM_FEEDBACK_PAUSED` or `GL_TRANSFORM_FEEDBACK_ACTIVE`.

`GL_INVALID_ENUM` error is generated by `glGetTransformFeedbacki_v` if `pname` is not `GL_TRANSFORM_FEEDBACK_BUFFER_BINDING`.

`GL_INVALID_ENUM` error is generated by `glGetTransformFeedbacki64_v` if `pname` is not `GL_TRANSFORM_FEEDBACK_BUFFER_START` or `GL_TRANSFORM_FEEDBACK_BUFFER_SIZE`.

`GL_INVALID_VALUE` error is generated by `glGetTransformFeedbacki_v` and `glGetTransformFeedbacki64_v` if `index` is greater than or equal to the number of binding points for transform feedback (the value of `GL_MAX_TRANSFORM_FEEDBACK_BUFFERS`).

## Version Support

| OpenGL Version
--- | ---
Function / Feature Name | 2.0 | 2.1 | 3.0 | 3.1 | 3.2 | 3.3 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5
`glGetTransformFeedbackiv` | - | - | - | - | - | - | - | - | - | - | - | ✔
`glGetTransformFeedbacki_v` | - | - | - | - | - | - | - | - | - | - | - | ✔
`glGetTransformFeedbacki64v` | - | - | - | - | - | - | - | - | - | - | - | ✔

## See Also

glBindBufferBase, glBindBufferRange, glBindBuffersBase, glBindBuffersRange, glBindTransformFeedback

## Copyright

Copyright © 2014 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/.