Difference between revisions of "GLAPI/glBeginTransformFeedback"

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[[Category:API Reference 4|BeginTransformFeedback]]
 
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[[Category:GL 4 API Transform Feedback|BeginTransformFeedback]]

Revision as of 23:32, 25 February 2012

glBeginTransformFeedback
Core in version 4.5
Core since version 3.0

glBeginTransformFeedback: start transform feedback operation

Function Definition

 void glBeginTransformFeedback(GLenum primitiveMode);
primitiveMode
Specify the output type of the primitives that will be recorded into the buffer objects that are bound for transform feedback.

Function Definition

 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/.