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 Feedback primitiveMode |
Allowed 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 Feedback primitiveMode |
Allowed 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/.
