GLBEGINCONDITIONALRE(3G)					   OpenGL Manual					  GLBEGINCONDITIONALRE(3G)

NAME

       glBeginConditionalRender - start conditional rendering

C SPECIFICATION

       void glBeginConditionalRender(GLuint id, GLenum mode);

PARAMETERS

       id
	   Specifies the name of an occlusion query object whose results are used to determine if the rendering commands are discarded.

       mode
	   Specifies how glBeginConditionalRender interprets the results of the occlusion query.

C SPECIFICATION

       void glEndConditionalRender(void);

DESCRIPTION

       Conditional rendering is started using glBeginConditionalRender and ended using glEndConditionalRender. During conditional rendering, all
       vertex array commands, as well as glClear() and glClearBuffer() have no effect if the (GL_SAMPLES_PASSED) result of the query object id is
       zero, or if the (GL_ANY_SAMPLES_PASSED) result is GL_FALSE. The results of commands setting the current vertex state, such as
       glVertexAttrib() are undefined. If the (GL_SAMPLES_PASSED) result is non-zero or if the (GL_ANY_SAMPLES_PASSED) result is GL_TRUE, such
       commands are not discarded. The id parameter to glBeginConditionalRender must be the name of a query object previously returned from a call
       to glGenQueries().  mode specifies how the results of the query object are to be interpreted. If mode is GL_QUERY_WAIT, the GL waits for
       the results of the query to be available and then uses the results to determine if subsequent rendering commands are discarded. If mode is
       GL_QUERY_NO_WAIT, the GL may choose to unconditionally execute the subsequent rendering commands without waiting for the query to complete.

       If mode is GL_QUERY_BY_REGION_WAIT, the GL will also wait for occlusion query results and discard rendering commands if the result of the
       occlusion query is zero. If the query result is non-zero, subsequent rendering commands are executed, but the GL may discard the results of
       the commands for any region of the framebuffer that did not contribute to the sample count in the specified occlusion query. Any such
       discarding is done in an implementation-dependent manner, but the rendering command results may not be discarded for any samples that
       contributed to the occlusion query sample count. If mode is GL_QUERY_BY_REGION_NO_WAIT, the GL operates as in GL_QUERY_BY_REGION_WAIT, but
       may choose to unconditionally execute the subsequent rendering commands without waiting for the query to complete.

NOTES

       glBeginConditionalRender and glEndConditionalRender are available only if the GL version is 3.0 or greater.

       The GL_ANY_SAMPLES_PASSED query result is available only if the GL version is 3.3 or greater.

ERRORS

       GL_INVALID_VALUE is generated if id is not the name of an existing query object.

       GL_INVALID_ENUM is generated if mode is not one of the accepted tokens.

       GL_INVALID_OPERATION is generated if glBeginConditionalRender is called while conditional rendering is active, or if glEndConditionalRender
       is called while conditional rendering is inactive.

       GL_INVALID_OPERATION is generated if id is the name of a query object with a target other than GL_SAMPLES_PASSED or GL_ANY_SAMPLES_PASSED.

       GL_INVALID_OPERATION is generated if id is the name of a query currently in progress.

SEE ALSO

       glGenQueries(), glDeleteQueries(), glBeginQuery()

COPYRIGHT

       Copyright (C) 2009 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/.

AUTHORS

       opengl.org

opengl.org							    06/10/2014						  GLBEGINCONDITIONALRE(3G)