Introduction Mouse
A mouse is essential to select objects and to use GAMGI efficiently.

### Object selection

Pressing, with the left button, one of the object labels on the top menu area, pops up a menu with all the available tasks for that object, which can subsequentially be selected with the mouse or with the keyboard.

Pressing a label in the main menu (above the window drawing area), with the middle button, means that the user is about to select an object of that class. If this class has a visual representation (atom, bond, molecule, cell, etc.), subsequently pressing the mouse over the visual representation of an object of this class results in the selection of the object.

If the selected class has no visual representation (light, layer, window, gamgi), or the visual representation is ambiguous, when it belongs to more than one object of the selected class (possible in recursive objects such as text, group, cluster, assembly), then a menu pops up, listing the possible objects, and allowing the selection of one, with the mouse or the keyboard.

A convenient short-cut to select the current layer, the current window and the current gamgi (everything), is to press twice over Layer, Window and Gamgi respectively, on the main menu.

### Dragging and pressing

Dragging the mouse over the window drawing area changes the selected object when Axes is off and the layer referential when Axes is on: 1) pressing the left button rotates the object (referential) around its geometric center along the three X,Y,Z axes: dragging horizontally rotates along the vertical axis, dragging vertically rotates along the horizontal axis, and dragging along a circular arc far from the center rotates along the axis perpendicular to the screen; 2) pressing the center button moves the object (referential) in the dragging direction; 3) pressing the right button up and down scales the object (layer) up and down respectively.

This functionality is available even for objects without visual representation, as lights. Dragging and pressing the left button when a directional or spot light is selected, changes the light direction. Dragging and pressing the middle button for a positional light, changes the light position. Dragging and pressing the right button for a spot light, changes the light angle.

When a task window for a given object class is open (as Atom Create, Layer Modify or Bond Remove), GAMGI attempts to use any mouse pressing over the drawing area to recognize an object of the same class, using the criteria described above to select an object (with or without visual representation).

When an object is found, its information is usually transported to the task window (and in some cases automatically executed), but this object does not replace the current object, which always needs to be explicitly selected: the two picking modes are independent.

To select an atom, for example, when Molecule Measure is open, just press the middle button over the Atom label on the main menu and click the mouse over the atom visual representation. Clicking again over the same atom, this time GAMGI is not expecting an object selection, so the default picking mode is executed and the molecule owning the atom is measured.

### Ruler handling

Pressing on Rotate, Move, or Scale (below the window drawing area) activates the positional ruler. This ruler is algebraic, centered around 0: for positive (counter-colockwise) changes, click on the right side of the ruler and for larger changes, click farther away from the ruler center.

Pressing again on rotate, move, or scale disables the ruler and its position returns to zero. Everytime an action is active, its label in the tool bar is highlighted, showing the default color again when disabled.
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