Chapter 12 pipeline monitoring of OpenGL super classic (version 7)

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Preface

Query the execution process of the command in the graphics pipeline
Measure command execution time
Synchronize applications with OpenGL And synchronized multiple OpenGL context

One 、 Inquire about

sketch ： Inquire about Opengl The execution status requires the creation of query objects , One object checks one question , After querying a question, you must delete a query object
glGenQueries()： Generate query objects
glDeleteQueries()： Delete query object
glGetError()： Query the execution result of the above function

1. occlusion query

sketch ： For those with high rendering costs , But objects that may not appear in the scene
application ：

glBeginQuery(...) # Start counting 
RenderSimplifiedObject(object) # Render low fidelity objects 
glEndQuery(...) # Stop count 
glGetQueryObjectuiv(..., &result) # Query and draw results 
if(result != 0)
	RenderRealObject(object) # Render complete objects 

Because rendering is done by pipeline , So many commands are queued , Not every time glEndQuery() when , All pixels are generated , Therefore, it is necessary to extend the time of query results .

Because the rendering command is sent to GPU There will be a lot of expenses , Some commands are executed only when the query object has results （ This method is called predicate ）, therefore opengl You can use the conditional rendering tool to send commands to GPU,glBeginConditionalRender() and glEndConditionalRender()

Advanced occlusion query ： Provide GL_ANY_SAMPLES_PASSED and GL_ANY_SAMPLES_PASSED_CONSERVATIVE Two Boolean occlusion queries complete the query target and count the exact number of samples that pass the depth test

Check regularly ： have access to glQueryCounter() The query in glBeginQuery() and glEndQuery() Operation time between execution of commands , Query results are expressed in nanoseconds ,32 Bit unsigned counts as slightly higher than 4 Nanoseconds per second , have access to glGetQueryObjectui64v() The query is higher than 4 The result of seconds and nanoseconds

The parameters for querying pipeline status can be seen in P369 page

Two 、OpenGL Sync

Use glFlush() mandatory Opengl Start processing commands or complete currently issued commands
GLsync glFenceSync()： Create a synchronization object
glGetSynciv()： Query synchronization status , See if the end of the pipeline is reached
glClientWaitSync() and gkWaitSync()： Waiting for synchronization signal
glDeleteSync()： Delete sync signal

There is no mechanism to reset the synchronization signal to the no signal state
Each synchronization object represents a one-time event