Conference bgsdev::open3d

>The so-called problem is related to object rotation started by mouse button
>down, mouse motion and stopped when mouse button left up.
>
>When you begin the mouse motion, the object rotation starts but when when you
>stop the motion, the object goes on rotating for while.

This is a classic problem dealing with OpenGL in the X11 windowing
system environment. The problem is that there are 3 queues --

	1. OpenGL rendering queue
	2. X11 rendering queue
	3. X11 input queue

and the application can put a lot of requests in the rendering queues.

Lets take the case where a frame takes 1 second to render, and the
mouse is moving and producing events every 1/10 second.

The application sees a mouse event at time t=0.0 and renders a frame.
Lets say it takes 5/10 second for the application to put 
frame 1 into the OpenGL rendering queue and call glXSwapBuffers (which
automatically flushes the 2 rendering queues.) It now looks at the
input queue and finds 5 new mouse events -- from t=0.1 to t=0.5. It compresses
the mouse events and renders frame 2 based on the mouse event at t = 0.5.
Frame 1 is only half done, so we have 1.5 seconds of rendering queued up.
After a few rounds of this, we can easily get tens of seconds of rendering
in the OpenGL rendering Queue.

The only solution to this is to throttle the application, and not let it
fill up the queues. We really can't do this effectively, which makes it up
to the application to throttle itself. It must do this by calling glFinish
every once in a while -- preferably every frame. This will stall the application
until time t=1 in our example above, so that there is never more than one
frame in the queue.

>The glutdino example does not show any delay in the rotation when the window
>has its initial size, but the problem occurs when the window is maximized.

The glut library as distributed by Digital should have a glFinish inside
the loop. From where did you get your glut library?

The size-dependent nature is because with a little window the frame
updates are fast enough to avoid the problem, but with a larger window
frames take longer to be rendered than the incoming mouse event stream allows.

>It does not exhibit the same behavior when I replace the ZLXp-L2 with a
>ZLXp-E3.

I don't understand why this would be the case.

>    - with ZLXp-E3, GLX treats only one stream for X events and OpenGL
>      rendering, so that you do not have to be concerned with synchronization 
>      issues
>
>    - with ZLXp-L and 4D40T, GLX treats separate streams for X events and 
>      OpenGL rendering, so that you have to write the synchronization code 
>      yourself  

The only difference with the -E3 is that the main CPU does more of the
work -- perhaps this is slowing down the application sufficiently.

>    - if you are working with GLX interface, you have to modify the X event
>      loop in order to make some event compression on MotionNotify events
>      so that you process these events only when there is no more job to do

This is required, but you also need to synchronize the input with the
rendering queue using glFinish.

>    - why not using glXWaitGL() to do explicit synchronization ?

glXWaitGL and glXWaitX only synchronize the two output queues, not the
event queue.

>    - how is it possible to implement synchronization if you are working with
>      the glut interface for which the event loop is managed by glutMainLoop()?

The glut library (__glutSetWindow) needs to be modified to put
the GLUT_FINISH_WORK item on the work list without regard to direct
or indirect rendering.

>    - Beginning with Open3D V4.2, direct rendering is available with PowerStorm
>      4D40T. Does this mean that the synchronization issue will not be so
>      critical ?

The direct rendering method used in the 4D40T series still requires the
application to self-throttle using glFinish.

Andy V

The glut library used is the one provided with O3DDWSGLBASE420 subset.

>The glut library used is the one provided with O3DDWSGLBASE420 subset.

That should certainly have the fix. If you install O3DDWSGLEXAMP420,
you should get the sources for libglut and you can look to see what is
happening.

Andy V

    Meanwhile, we are working with Pro/Engineer to get a fix incorporated
    into their product(s).
    
    	George