Open CASCADE notes

With recently released CAD Exchanger 2.1 Beta, which adds some GUI improvements, I thought to share some experience about that.
Default OCC viewer suggests some conventions based on using the Ctrl button and mouse buttons:
- Ctrl + MB1 (left button) – zoom;
- Ctrl + MB2 (middle button) – pan;
- Ctrl + MB3 (right button) – rotate.
This seems to be not only inconsistent with typical conventions in CAD systems but also challenging for user experience. For instance, MB3 is normally expected to open a context menu.
So following CAD Exchanger users’ feedback, I had to implement different navigation based on Solidworks and other conventions. They are based on using MB2:
- MB2 – rotate
- Shift + MB2 – zoom
- Ctrl + MB2 – pan.


In addition, support for mouse wheel (to zoom in/out), which is a commonly used convention, has been added. For Qt-based viewer it appeared to be quite easy:

void QOOcc_View3d::wheelEvent (QWheelEvent* theEvent)
{
if (theEvent->orientation() == Qt::Vertical) {
int numDegrees = theEvent->delta() / 8; //number of degrees the wheel rotated by
//let 100 degrees be approximately 2x zoom (see V3d_View::Zoom())
int numSteps = numDegrees;

myView->Zoom (0, 0, numSteps, 0);
theEvent->accept();
}
}

Apparently, QtOCC project by Peter Dolby already implemented that (though I did not notice). But Peter used V3d_View::SetScale(). Either should work anyway.

Perhaps, wheel support could be added into default OCC viewers and default OCC conventions could be revisited to better align with industrial ones.