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GLBEGINTRANSFORMFEED(3G)                         OpenGL 3.3                         GLBEGINTRANSFORMFEED(3G)



NAME
       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 |                         Allowed                 |
       |Feedback primitiveMode            | 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 |                         Allowed  |
       |Feedback primitiveMode            | 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 (C) 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/.



OpenGL 3.3                                       03/08/2011                         GLBEGINTRANSFORMFEED(3G)