SAOimage display of M-51

SAOimage Mouse Control

SAO/TDC Home Page
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.


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.