|Core in version||4.6|
|Core since version||3.0|
glBeginTransformFeedback: start transform feedback operation
void glBeginTransformFeedback(GLenum primitiveMode);
- Specify the output type of the primitives that will be recorded into the buffer objects that are bound for transform feedback.
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 Feedback primitiveMode||Allowed Render Primitive modes|
|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 Feedback primitiveMode||Allowed Geometry Shader Output Primitive Type|
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.
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.
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