
mouse control in SAOimage

As with most interactive workstation programs, SAOimage uses the mouse
and its buttons for many of its interactions.  To take full advantage of
SAOimage's features, the user must understand how to use the mouse.
There are three basic types of mouse interactions: moving, clicking, and
dragging.  Moving means moving the mouse while keeping it flat on its
mouse pad or desk surface.  Clicking means pressing one of the buttons
on the mouse and then releasing it.  Dragging means holding one or more
of the mouse's buttons down while moving the mouse.  Rotating the mouse
is not a meaningful action.

The mouse is represented on the screen by an "icon", a simple symbol
about a half centimeter on a side, which moves on the screen as you move
the mouse on your table.  The box with buttons which you hold in your
hand and the icon on the screen are interchangeably (or in concert)
referred to as the mouse.  In X11 literature, the mouse is commonly
referred to as the "pointer."  The mouse "occupies" a window or object
when its icon on the screen is within the borders of that window or
object.  The mouse interaction (as well as the keyboard interaction)
is governed by the window or object which the mouse occupies.

The mouse icon has a point (called the "hot spot") which is used to
determine its screen coordinates.  This point is usually in the center of
the icon or at a corner.  The shape of the icon should make it easy to
guess where the hot-spot is.  The mouse location (or "where the mouse
is pointing") refers to the hot-spot.  Often dragging is initiated by
pointing the mouse at a particular object (i.e. the vertex of a graph or
polygon) as the appropriate mouse button is pressed, and then "dragging"
that object while continuing to hold the mouse button down.

Some interactions may be performed while dragging with more than one
mouse button down at the same time.  In the color graph, for example,
each mouse button corresponds to one of the three display colors (red,
green, blue).  One can make a change in gray level, by dragging with
all three buttons held down while moving the graph vertex.

Some actions perform a completion action only after the last mouse
button is released.  For example, consider the pan window interaction.
In the pan window, you may manipulate both the magnification and the
center of the main display window (zoom and pan).  The main display
window is not actually redrawn until all mouse buttons are released.
The area that would appear in the main display window, if the mouse
buttons were released at that point, is represented by a box drawn in
the pan window.  You may switch directly from adjusting the zoom to
adjusting the pan (or visa-versa) by pressing the other mouse button
down while still holding the former button down.

tracking

Some interactions actually "track" the mouse.  By this we mean that that
which is being controlled is repeatedly updated as the mouse is moved,
giving the impression of smooth, continuous change.  An example of this
is moving a cursor with the mouse.  As you move the mouse, the displayed
cursor moves across the screen.  Another example is the magnifier window.
As you move the mouse, the view in the magnifier shifts (or pans), as if
watching moving scenery.

While tracking is generally desirable, your workstation processor may
not be fast enough to make many repeated updates for the illusion of
smooth continuous change.  This is especially a problem for complicated
processes (e.g. redrawing the main display window or drawing several
elliptical annuli) or when many things are all tracking at the same time
(e.g. changing the colors while also updating the graph which represents
the color map).  When this happens, the effect of moving the mouse may
lag annoyingly behind the actual movement of the mouse.

Recognizing that some processors are slower than others, SAOimage allows
some tracking actions to be enabled or disabled.  The magnifier window
can track the mouse as it moves across the main display or pan windows.
The color table graph can track changes to the color map as they are
controlled either in the main display window or directly on the graph
(see the Color section).  Both of these tracking functions are enabled
or disabled by the "track" button in the "etc" button submenu.  The
"track" selection can be overridden (reversed) temporarily by pressing
the "Shift" key or more long term by toggling the "Caps lock" key.  The
running text display of the mouse coordinates and the corresponding pixel
value can be enabled or disabled by the "coord" button in the "etc"
button submenu.  This is also overridden by the "Shift" and "Caps" keys. 

fine movement

SAOimage uses the user's default mouse movement velocity settings.  To
move the mouse one pixel at a time in any direction, use the keyboard
arrow keys (see the Keyboard section).  The arrow keys can be used at any
time in place of physically moving the mouse.  Thus to perform a fine
movement while dragging, hold the mouse steady with the mouse button (or
buttons) depressed with one hand, while pressing the appropriate arrow
keys with the other hand.  If you are not already tracking, you may wish
to hold the shift key down as you do so, to better see the effect of the
fine movements.
