glBeginTransformFeedback

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Start transform feedback operation.

C Specification[edit]

void glBeginTransformFeedback( GLenum primitiveMode );
void glEndTransformFeedback(  void );


Parameters for glBeginTransformFeedback[edit]

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


Description[edit]

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[edit]

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[edit]

 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 glBeginTransformFeedback if any binding point used in transform feedback mode does not have a buffer object bound.

 GL_INVALID_OPERATION is generated by glBeginTransformFeedback 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.


Version Support[edit]

 glBeginTransformFeedback  3.0+
 glEndTransformFeedback  3.0+

See Also[edit]

Copyright[edit]

Copyright© 2010-2014 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/.