Hi Gianluca, If you new exactly what objects needed updating then you could compute combined bounding volume of the modified objects in the current and the previous frame and then project these combined bounding volume into screen space to find out the region of the screen that will need to be redrawn.
Once you know the region of the screen that needs redraw then you could adjust the viewer's Camera so that it has a smaller viewport and adjust projection matrix to just render the area of interest. This approach would also have to render to the front buffer rather than the back buffer, and with it would have a small flicker when the region is redrawn. To get around the flicker you could draw the full screen twice and then draw the updated region on each new frame. You'll need to update the region between the objects position two frames ago and the current position rather than the just the region covered by the two adjacent frames. As you'll gather all this is doable, but rather convoluted, just rendering the whole frame when needed will certainly lead to an easier life and lower application complexity. Robert. On Tue, Feb 22, 2011 at 1:47 PM, Gianluca Natale <[email protected]> wrote: > Hi there, > I hope someone of you can help me on this issue. > I have a very complicated scene graph, that takes a very long time to be > completely redrawn (>200 ms). > > But the most frequent use case I have is to redraw only a very small part of > the model at a time > (suppose for example that I would need to redraw only the object under the > mouse). > > So, I could increase performances a lot by simply redrawing that object in > the front buffer without clearing the depth buffer, > in order to keep it in the right position WRT the other object of the model. > And without swapping front and > back buffers at the end of drawing. > > Is this possible? > > > > If I’m not wrong, sometimes ago I received an email from you saying that the > drawing traversal of OSG > > always clean the depth and back buffers, redraws the complete scene graph > and then swap the buffers. > This works pretty well when the scene changes dynamically, but in my case > where there is a static drawing for > > a long time, I would need a way to tell the drawing traversal to draw in the > front buffer, and not to perform the swapping > of buffers at the end. > > Is there a way to do that? > > > > Thanks in advance > > Gianluca Natale > > > > _______________________________________________ > osg-users mailing list > [email protected] > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
