Re: [osg-users] preDrawCallback?

Mon, 04 May 2009 11:46:22 -0700

I'm confused about the code that does the resize in GraphicsContext.cpp (part is pasted below).
In my case, my background camera is a slave camera with an absolute reference frame.
So, it isn't going to be caught in the if statement on line 7 and will fall through to the else. In this block, it is going to test the resize policy of the main camera rather than my slave (line 18). In my app, the main camera has a HORIZONTAL resize policy.

Is it incorrect to have a slave with an absolute frame that differs from the main camera's?


 1: // if aspect ratio adjusted change the project matrix to suit.
 2: if (aspectRatioChange != 1.0)
 3: {
 4:   osg::View* view = camera->getView();
 5:   osg::View::Slave* slave = view ? view->findSlaveForCamera(camera) : 0;
 6:  
 7:   if (slave && camera->getReferenceFrame()==osg::Transform::RELATIVE_RF)
 8:   {
 9:     switch(view->getCamera()->getProjectionResizePolicy())
10:     {
11:       case(osg::Camera::HORIZONTAL): slave->_projectionOffset *= osg::Matrix::scale(1.0/aspectRatioChange,1.0,1.0); break;
12:       case(osg::Camera::VERTICAL): slave->_projectionOffset *= osg::Matrix::scale(1.0, aspectRatioChange,1.0); break;
13:       default: break;
14:     }
15:   }
16:   else
17:   {
18:     Camera::ProjectionResizePolicy policy = view ? view->getCamera()->getProjectionResizePolicy() : camera->getProjectionResizePolicy();
19:     switch(policy)
20:     {
21:       case(osg::Camera::HORIZONTAL): camera->getProjectionMatrix() *= osg::Matrix::scale(1.0/aspectRatioChange,1.0,1.0); break;
22:       case(osg::Camera::VERTICAL): camera->getProjectionMatrix() *= osg::Matrix::scale(1.0, aspectRatioChange,1.0); break;
23:       default: break;
24:     }
25:   }
26: }  

Cory


Robert Osfield wrote: 
On Mon, May 4, 2009 at 3:08 PM, Cory Riddell <[email protected]> wrote:
  
Thanks Robert and Paul. I just assumed that a direct GDI call would be
faster, but when I think about it, that can't be true (assuming a decent
OpenGL driver).

I did as you suggested and it works very well. Mostly.

If I resize the window and make it wide and short, my background gradient
maintains it's aspect ratio and blue bars on the sides are soon revealed. Do
I need to add code to my event handler to recompute the background scene
during resize events?
    

You attach Camera's directly to the GraphicsWindow, and if you do this
then the GraphicsWindow will do the resize of the viewport and
(optionally) the projection matrix as well.  The on screen stats uses
a Camera in this fashion so have a look at the implementation in
src/osgViewer/StatsHandler.cpp.

If the GraphicsWindow doesn't know about your Camera they you'll need
to manage the resize yourself.

Robert.
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