Provided by: opengl-4-man-doc_1.0~svn22917-1_all 
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