I want to emulate shutter time with OpenGL. I found this below gives the best results:

ClearScene();

DrawScene();

DrawMovingObject();

glAccum(GL_LOAD, 1.0/n );

for (i=1; i<n; i++)
{
ClearScene();

DrawScene();

DrawMovingObject();

glAccum(GL_ACCUM, 1.0/n );
}

glAccum(GL_RETURN, 1.0);

However, this code is pretty slow as the entire scene needs to be drawn every single time. If I omit the ClearScene() and DrawScene() part from the for loop, I get a motion blurring effect that however does not look like the effect of a shutter on a camera that I would like to obtain. Any ideas on how to do this faster (copying frame buffer, how)?