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GLBEGINTRANSFORMFEED(3G)	 OpenGL Manual	      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 © 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/.

AUTHORS
       opengl.org

opengl.org			  03/16/2013	      GLBEGINTRANSFORMFEED(3G)

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