OpenGL extension ARB.transform_feedback3
This module customises the behaviour of the OpenGL.raw.GL.ARB.transform_feedback3 to provide a more Python-friendly API
Overview (from the spec)
This extension further extends the transform feedback capabilities provided by the EXT_transform_feedback, NV_transform_feedback, and NV_transform_feedback2 extensions. Those extensions provided a new transform feedback mode, where selected vertex attributes can be recorded to a buffer object for each primitive processed by the GL.
This extension provides increased flexibility in how vertex attributes can be written to buffer objects. Previous extensions allowed applications to record a set of attributes interleaved into a single buffer object (interleaved mode) or to record into multiple objects, but with only a single attribute per buffer (separate mode). This extension extends interleaved mode to write into multiple buffers, with multiple attributes per buffer. This capability is supported for all three styles of transform feedback:
  • "EXT"-style GLSL transform feedback (EXT_transform_feedback), where a list of varyings is provided prior to linking a program object and is used whenever that program object is used.
  • "NV"-style GLSL transform feedback (NV_transform_feedback), where "locations" of active varyings are queried after linking and are then passed to a function that sets the active transform feedback varyings for the program object. Unlike the "EXT"-style mode, the set of varyings to capture can be changed without relinking.
  • Transform feedback for fixed-function or assembly vertex/geometry shaders (NV_transform_feedback), where applications specify a set of canonical attribute enums/numbers to capture.
Additionally, this extension adds new support for multiple separate vertex streams. New geometry shader functionality provided by the ARB_gpu_shader5 and NV_gpu_program5 extensions allows geometry shaders to direct each vertex arbitrarily at a specified vertex stream. For example, a geometry program might write each "regular" vertex it emits to one vertex stream while writing some per-primitive data it computes to a second vertex stream. This extension allows applications to choose a vertex stream for each buffer object it writes to, and allows the vertices written to each vertex stream to be recorded in separate buffer objects. Only one stream may be selected for rasterization, and in the initial implementation, the geometry shader output topology must be POINTS if multiple streams are used. When geometry shaders are not used, or when an old geometry shader not writing multiple streams is used, all vertices produced by the GL are directed at the stream numbered zero. The set of transform feedback-related query targets is extended to accommodate multiple vertex streams, so it is possible to count the number of processed and recorded primitives for each stream separately.
The official definition of this extension is available here:


glBeginQueryIndexed( target , index , id )
glDrawTransformFeedbackStream( mode , id , stream )
glEndQueryIndexed( target , index )
glGetQueryIndexediv( target , index , pname , params )