OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Starting and Stopping Transform Feedback

Transform feedback can be started and stopped, and even paused. As might be expected starting transform feedback when it is not paused causes it to start recording into the bound transform feedback buffers from the beginning. However, starting transform feedback when it is already paused causes it to continue recording from wherever it left off. This is useful to allow multiple components of a scene to be recorded into transform feedback buffers with other components rendered in between that are not to be recorded.

To start transform feedback, call glBeginTransformFeedback().

void glBeginTransformFeedback(GLenum primitiveMode);

Sets the primitive type expected to be recorded by transform feedback.