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 © 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