glBeginConditionalRender

glBeginConditionalRender: man3/glBeginConditionalRender.xml

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.

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.