glFinish()vs glFenceSync()+ glClientWaitSync()

跑步之间有区别吗？

glFinish()

并运行

glFenceSync(...)
glClientWaitSync(...)

大超时？

我正在尝试做的事情:我运行一个OpenGL命令管道,我想要计算每个命令需要多长时间.如果没有上述任何命令,一切都将被流水线化/缓冲,并且看起来最后一个命令占用了所有处理时间.

timer start

Run Opengl part 1

sync / glFinish
timer measure

Run Opengl part 2

sync / glFinish
timer measure

...

所以我试图弄清楚如何最好地测量各个部件的"速度",而不会影响整个运行时间.

您提到的所有选项都会影响应用程序的性能,因为它们会使管道停滞不前.在OpenGL中测量时序的现代方法是使用Timer Queries:告诉OpenGL它应该在GPU上执行查询时保存时间戳,因此不需要GPU和CPU之间的同步.例如,代码看起来像这样:

GLuint64 startTime, stopTime;
unsigned int queryID[2];

// generate two queries
glGenQueries(2, queryID);
...
// issue the first query
// Records the time only after all previous 
// commands have been completed
glQueryCounter(queryID[0], GL_TIMESTAMP);

// call a sequence of OpenGL commands
...
// issue the second query
// records the time when the sequence of OpenGL 
// commands has been fully executed
glQueryCounter(queryID[1], GL_TIMESTAMP);
...

// get query results
// (automatically blocks until results are available)
glGetQueryObjectui64v(queryID[0], GL_QUERY_RESULT, &startTime);
glGetQueryObjectui64v(queryID[1], GL_QUERY_RESULT, &stopTime);

printf("Time spent on the GPU: %f ms\n", (stopTime - startTime) / 1000000.0);

(代码取自Lighthouse3d.com).

另一种选择是使用glBeginQuery与GL_TIME_ELAPSED参数,其也被链接的文章中描述.