In order to use the Transform Feedback functionality, you need to configure the Transform Feedback Buffer indexed bindings. This can be achieved by either using glBindBufferBase or glBindBuffersBase to associate whole buffer object storage to one of the Transform Feedback Binding Points, or by calling glBindBufferRange or glBindBuffersRange to use a region of a buffer object storage for the binding. You may want to (but are not required to) bind a Transform Feedback Object first, in order to cache the binding configuration. This usually allows you to restore the Transform Feedback configuration faster, than if you were to execute a list of API calls necessary to set up the Transform Feedback state of your liking.
This reference page discusses two types of getters that operate on Transform Feedback Objects and their bindings.
The first class operates on general Transform Feedback binding point and includes glGetTransformFeedbackiv function. glGetTransformFeedbackiv can be used to retrieve information about Transform Feedback object bound to the general Transform Feedback binding point, as configured with a glBindTransformFeedback call. In this case, you can check:
The latter class, which includes glGetTransformFeedbacki_v and glGetTransformFeedbacki64_v functions, can be used to check what the current configuration of each of the buffer object regions bound to Transform Feedback Buffer binding points is. This allows you to query for the following information:
GL_INVALID_OPERATION error is generated if xfb is not zero or the name of an existing transform feedback object.
GL_INVALID_ENUM error is generated by glGetTransformFeedbackiv if pname is not GL_TRANSFORM_FEEDBACK_PAUSED or GL_TRANSFORM_FEEDBACK_ACTIVE.
GL_INVALID_ENUM error is generated by glGetTransformFeedbacki_v if pname is not GL_TRANSFORM_FEEDBACK_BUFFER_BINDING.
GL_INVALID_ENUM error is generated by glGetTransformFeedbacki64_v if pname is not GL_TRANSFORM_FEEDBACK_BUFFER_START or GL_TRANSFORM_FEEDBACK_BUFFER_SIZE.
GL_INVALID_VALUE error is generated by glGetTransformFeedbacki_v and glGetTransformFeedbacki64_v if index is greater than or equal to the number of binding points for transform feedback (the value of GL_MAX_TRANSFORM_FEEDBACK_BUFFERS).
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