Panning and zooming a component, Computer Graphics

Panning and zooming Components (such as your Polybounce or Animation) is simply a matter of reFrameing the world window. To pan right or left horizontally, one shifts it in the positive or negative x direction, respectively. To pan up or down vertically one shifts it in the positive or negative y direction. If factor is the fraction of the world window that you want to pan, these can be implemented as:

// Horiz. pan --- Pan left moves world window left void Polybounce::panH(double factor)
{
reFrame(world()+Point2(w_width()*factor,0));
}
// Vert. pan --- Pan up moves world window down
void Polybounce::panV(double factor)
{
reFrame(world()+Point2(0,w_height()*factor));
}

To zoom in or out, one needs to resize the world window either smaller or larger, respectively, without changing the center of the window. You can do this by ?rst translating the center of the window to the origin, then scaling the window (using scalar multiplication of RealRects), then translating it back to its original center.

This still only takes a few lines of code. If scale is the scaling factor:

// Zoom
void Polybounce::zoom(double scale)
{
Point2 center( (world().left()+world().right())/2,
(world().bottom()+world().top())/2 );
// translate to origin
reFrame(world()-center);
// scale by getZoom
reFrame(world()*Point2(scale,scale));
// translate back
reFrame(world()+center);
}

To add panning and zooming to your Polybounce without pan and zoom sliders,you can simply add keyboard events for these which just pan by a ?xed fragment,1/4 of the window, say, and zoom by ?xed scaling factors, perhaps 1/2 for zoom in and 2 for zoom out. These could be added to the Polybounce class, but they will need to be passed from the Display class anyway, so there is no reason to not just call the pan and zoom functions directly from Display's keyboard event handler.

Posted Date: 3/14/2013 1:18:16 AM | Location : United States







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