glBeginTransformFeedback — start transform feedback operation
void glBeginTransformFeedback( | GLenum | primitiveMode); |
primitiveModeSpecify the output type of the primitives that will be recorded into the buffer objects that are bound for transform feedback.
void glEndTransformFeedback(void);
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
|
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.
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/.