Keyboard Shortcuts

The Keyboard Shortcuts extension allows simple keyboard shortcuts (accelerators) to be used for many operations in Chimera. See also: general keyboard shortcuts

Use of these shortcuts is disabled by default, but can be turned on:

• with the command ac
• by starting Keyboard Shortcuts (for example, with Tools... General Controls... Keyboard Shortcuts) and turning on Enable keyboard shortcuts in the dialog

• with the accelerator af
• with the accelerator cl (also shows the Command Line)
• by turning off Enable keyboard shortcuts in the dialog

Many accelerators are included with Chimera, and more can be added. They usually consist of two characters, but any number of characters is possible. Uppercase letters are sometimes used and are distinct from lowercase. Several provide capabilities not accessible through the graphical interface. Keyboard shortcuts are not entered in the Command Line except via the command ac.

There are several ways to start Keyboard Shortcuts, a tool in the General Controls category. The resulting dialog lists the known accelerators along with brief descriptions. Clicking on an entry in the list shows a more detailed description (if available) at the bottom of the dialog.

• Filter list limits the entries to those containing the entered text.
• Enable keyboard shortcuts controls whether accelerators are enabled.
• Show main window status line controls whether a status line is shown under the Chimera window. Keystrokes interpreted as accelerators and messages reporting their effects appear in the status line.
• Load shortcuts file reads accelerator definitions from the Python file whose pathname is shown in the field below. New keyboard shortcuts can be added by putting their definitions in a Python file and then using Load.
• Key press time-out (seconds) (default 2) controls how long keystrokes that form part of an accelerator are remembered.

Keystrokes may be interpreted as accelerators, as commands, or as information intended for other dialogs. Sometimes it is necessary to click in the graphics window or Side View to take back focus from some other dialog so that accelerator or command keystrokes will register.

An accelerator takes effect as soon as it is typed; there is no need to press return (Enter). A command takes effect after return is pressed. How these forms of input are distinguished:

• If accelerators are on and the Command Line has not been shown, keystrokes are interpreted as accelerators when the mouse focus is in the graphics window.
  
  
• To allow both types of input, accelerators should be turned on after the Command Line has been shown. If the Command Line is started after accelerators, it will receive all of the keystrokes, even if subsequently hidden or quit. In this situation, to enable both types of input:
  • turn or toggle accelerators on again
  • use the command ac
  
  
• When both types of input are enabled as described above, one must click in the graphics window to indicate that keystrokes should be interpreted as accelerators and click in the command-line area to indicate that keystrokes should be interpreted as commands.

Keystrokes being interpreted as accelerators are shown in the status line; the time-out setting controls how long a partial accelerator entry is retained. If the wrong key has been pressed, simply waiting for the time-out period to elapse allows a fresh start. Alternatively, pressing the escape key clears the partial accelerator from memory. Finally, if no accelerator starts with the key that has been pressed, an “unknown accelerator” status message results and the keystroke is not retained. Completed accelerator operations are reported in the status line and Reply Log.

The standard Chimera keyboard shortcuts are defined in

share/Accelerators/standard_accelerators.py

Example file:

def register_accelerators():

  from Accelerators import standard_accelerators
  standard_accelerators.register_accelerators()

  from Accelerators import add_accelerator
  add_accelerator('ry', 'Rotate models about y axis', rotate_y)
  add_accelerator('rs', 'Stop model rotation', stop_rotation)

def rotate_y():
  'Spins models about the y axis'
  import Midas
  Midas.roll(axis = 'y')

def stop_rotation():
  'Stops spinning models'
  import Midas
  Midas.freeze()

The register_accelerators() function is called by the Accelerators extension. The first two lines load the standard accelerators. The next three lines define accelerators ry and rs to spin the models about the Y axis and to stop the spinning. The routines that spin and stop the spinning use the Chimera Midas module. The comment strings in the add_accelerator lines are the short descriptions that appear in the top part of the Keyboard Shortcuts dialog and, when the accelerator operation is performed, in the status line; the comment string within each function is the explanation shown at the bottom of the Keyboard Shortcuts dialog when the accelerator list entry is clicked.

Since accelerators take effect immediately (without return), a new accelerator cannot start with an existing accelerator. For example, if ab is a known accelerator, accelerators of the form abx, where x is any character, cannot be used.

A click in the graphics window or Side View may be required.
Sometimes it is necessary to click in the graphics window or Side View to take back focus from some other dialog so that accelerator or command keystrokes will register.

“Off by one” situations can occur.
Suppose sv (open the Side View) is intended, but “xv” is typed accidentally. If there is no accelerator starting with “x,” an “unknown accelerator” status message results and only the “v” is retained in memory. If sv is then typed before the time-out period has elapsed, the keystrokes will be interpreted as the accelerator vs (show volume) and another “v” is retained in memory until the time-out period has again elapsed (or the escape key is pressed).

Accelerators are not shown on menu entries, nor are they available for all menu functions.
Potential improvements include showing accelerators on the corresponding menu entries to make them easier to learn, and defining accelerators for more menu functions.