
SAOimage pan and zoom

The loaded image may be panned and/or zoomed for its display in the
central display window.  Panning and zooming are interactively
controlled by clicking or dragging the mouse in the pan window.
This is the small image window at the top of the desktop, next to
the magnifier.

The pan window shows the entire area of the loaded image.  (By
default the image in the pan window was reduced by taking the
maximum value in each block of the original image, but averaging,
summing, or subsampling may be used instead - see the cmdline
section).  A box cursor in the pan window shows the area of the
image currently being displayed in the main display window.  This
box can be moved and sized just like the regular box cursor (but
without angular rotation control).

The left mouse button controls the location of the center of the
box (the display image).  The middle button controls the edge of
the box, for the given center, thus determining its size.  The
size of the box is restricted to integer zoom factor.  (The
actual algorithm choses the smallest zoom that still includes the
mouse pointer's position.)  One can switch from one type of
control to the other, by holding the first button down, until
after the second button has been pressed.  The interaction
can be cancelled by dragging the pointer outside of the pan
window's borders.  Only after the last button is released is
the main display redrawn, with the indicated pan and zoom.

When the mouse is in the pan window, the area under the mouse
pointer can be magnified in the magnifier by pressing or holding
the shift key on the keyboard.  The "T" key table also works
with the pointer in the pan window (see the keyboard section).
As anywhere else, the arrow keys can be used for fine
positioning.

In pan mode, the same types of interactions as those used in
the pan window can be performed in the main display window.
Clicking or dragging with the left button controls the center
of the display.  Clicking or dragging with the middle button
determines the zoom factor.  The box cursor in the pan window
tracks these manipulations as the mouse is dragged in the
display window, just as it does when it is being directly
manipulated in the pan window.

The "pan" submenu allows a more basic method of changing the
zoom (e.g. x4 or x1/2).  The center button centers the display
on the image and the zoom 1 sets it to one display pixel per
image pixel.
