请问openGL中glEndQuery(GL_TIME_ELAPSED);是做什么的？

[AnnaChen1209]

void RenderGPU() {
	SetOrthographicProjection();
	glViewport(0,0,texture_size_x, texture_size_y);
	CHECK_GL_ERRORS
	
	glBeginQuery(GL_TIME_ELAPSED,t_query);
	for(int i=0;i<NUM_ITER;i++) {
		glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fboID[writeID]);	
		glDrawBuffers(2, mrt);	
		
		CHECK_GL_ERRORS
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, attachID[2*readID]);
		
		CHECK_GL_ERRORS
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, attachID[2*readID+1]);
		
		glClear(GL_COLOR_BUFFER_BIT);
		glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

		verletShader.Use();			
			verletShader.AddUniform("ellipsoid_xform");	glUniformMatrix4fv(verletShader("ellipsoid_xform"), 1, GL_FALSE, glm::value_ptr(ellipsoid));			
			verletShader.AddUniform("inv_ellipsoid");	glUniformMatrix4fv(verletShader("inv_ellipsoid"), 1, GL_FALSE, glm::value_ptr(inverse_ellipsoid));			
		//verletShader.AddUniform("ellipsoid");		glUniform4f(verletShader("ellipsoid"),center.x, center.y, center.z, radius);
			DrawFullScreenQuad();
		verletShader.UnUse();
		
		
		//swap read/write pathways
		int tmp = readID;
		readID  = writeID;
		writeID = tmp;
	}
	
	//glFlush();
	//glFinish();
				
	CHECK_GL_ERRORS						
	ResetPerspectiveProjection();

	//read back the results into the VBO
	glBindFramebuffer(GL_READ_FRAMEBUFFER, fboID[readID]);

	glReadBuffer(GL_COLOR_ATTACHMENT0); 			
	glBindBuffer(GL_PIXEL_PACK_BUFFER, vboID); 			
	glReadPixels(0, 0, texture_size_x, texture_size_y, GL_RGBA, GL_FLOAT, 0); 
	//glFlush();
	//glFinish();
	glEndQuery(GL_TIME_ELAPSED);

这段代码中，glBeginQuery(GL_TIME_ELAPSED,t_query);和glEndQuery(GL_TIME_ELAPSED);报错是什么原因？不是代码问题，可能是我配置的问题

[AnnaChen1209]

已解决 参考 http://www.opengl.org/discussion_boards/showthread.php/171554-How-to-measure-timing-in-OpenGL/page2 Oh, ok! That's the problem. You haven't included glext.h properly. You can just add the following code, so that timer query constant are defined. #ifndef GL_ARB_timer_query #define GL_TIME_ELAPSED 0x88BF #define GL_TIMESTAMP 0x8E28 #endif Or use value 0x88BF instead of GL_TIME_ELAPSED.