A Chimera preferences file contains settings from the Preferences dialog and additional information such as recently accessed files and directories.

A particular preferences file can be specified with --preferences at startup. Otherwise, Chimera will look for a file named preferences first in the current directory, then in a .chimera subdirectory of the current directory, then in the .chimera subdirectory of the user's home directory. On Windows, the user's home directory depends on a user's profile, but is often C:\Documents and Settings\username\Application Data\. The file location is reported in the Preferences preferences. Preference changes and other information from the current session will be saved to this file unless it has been designated read-only.

This system allows a user to maintain a single set of preferences for all Chimera sessions, or different preferences specific to data in different directories, or a combination of these.

If no preferences file is found, Chimera will look for a writable location for a new preferences file in the following order: the user's home directory (a subdirectory .chimera with a preferences file within it will be created), a subdirectory .chimera of the current directory, the current directory. If none of these directories are writable, an error message will appear.

Choosing Favorites... Preferences from the menu opens the Preferences dialog. Options within are grouped by Category:

• Background
• General
• Image Credits
• Messages
• Midas
• Mouse
• New Molecules
• New Surfaces
• PDB
• POV-Ray Options
• Preferences
• Tools
• Web Access

Help opens this manual page in a browser window, and Close dismisses the Preferences dialog.

Default settings are indicated below in bold.

The Background section of the Preferences dialog includes:

• Background color (a color well, No Color by default) - when set to No Color, the background is black
• Label font (Sans Serif/Serif/Fixed) (Normal/Bold/Italic/Bold Italic) (6/8/9/10/11/12/16/18/24/30/36)
• Selection highlight method (outline/fill) - how a selection is highlighted in the graphics window
• Selection highlight color (a color well, green by default) - what color to use for highlighting a selection in the graphics window
• Draw lens borders (true/false) - whether to draw outlines of any lenses in the graphics window
• Lens border color (a color well, green by default) - what color to use for outlining any lenses in the graphics window

The General section of the Preferences dialog includes:

• Confirm exit (true/false) - whether to ask for confirmation before exiting Chimera when File... Quit has been chosen or the command stop has been entered (does not apply to occurrences of stop in command files)
• Show balloon help (true/false) - whether to show balloon help, explanatory text that pops up when the cursor is left in certain positions
• Show atomspec balloon (true/false) - whether to show information in a balloon when the cursor is left over an atom or bond in the graphics window. The number of decimal places shown for bond distances can be set with the Distances tool.
• Atomspec display style (simple/command-line specifier) - whether to describe atoms with a simple style that consists of residue name, residue specifier (number.chain), and atom name, or with an atom specification string that could be used in the Command Line (affects atomspec balloons and the Structure Measurements panels)
• File lists path style (file - leading path/full path) - how to list files and their locations in certain dialogs (such as Files to read at startup within the Midas preferences); a change will not be evident until after Chimera is restarted
• Fullscreen graphics (true/false) - whether the graphics window is in fullscreen mode (Windows only)
• Toolbar side (left/right/top/bottom) - position of the toolbar relative to the graphics window (the toolbar is only shown when it contains one or more icons, as specified in the Tools section)
• File browser confirms overwrite (true/false) - whether to ask for confirmation before overwriting a file with a save dialog
• Use short open/save browser (true/false) - whether open/save dialogs should show only the two lowest directory levels (more details)
• Open dialog starts in directory from last session (true/false) - whether the first open/save dialog invoked during a session should start in the directory where a file was last opened or saved in the previous session, or in the current working directory. The default is true on Windows systems, false on the others.

The Image Credits section of the Preferences dialog specifies information to be included in saved image files (TIFF, PNG). This information does not affect the image itself.

• Artist (user's login name by default) - optional, name of the image creator
• Copyright (blank by default) - optional, a copyright statement

The Messages section of the Preferences dialog controls the disposition of command, status, warning, and error messages.

• Show status line (true/false) - whether to show a line for status messages under the main Chimera window (otherwise, status messages are not visible); can also be set from the Accelerators dialog
• Clear status line after (5 seconds/10 seconds/20 seconds/30 seconds/1 minute/never) - how long a status message will be shown in the status line (when not overwritten by subsequent status messages); applies to status messages appearing in certain dialogs as well as the main Chimera status line
• Command (reply log only/dialog) - whether command messages should appear in the Reply Log only, or also generate a dialog box
• Warning (reply log only/dialog) - whether warnings should appear in the Reply Log only, or also generate a dialog box
• Error (reply log only/dialog) - whether error messages should appear in the Reply Log only, or also generate a dialog box

The Midas section of the Preferences dialog is only available after the Command Line (formerly known as the Midas Emulator) has been shown.

Files to read at startup refers to what command files, if any, should be executed when the Command Line is started. There are two defaults:

• $HOME/.chimera/midasrc (in a directory named .chimera in the user's home directory; on Windows, this depends on a user's profile but is often C:\Documents and Settings\username\Application Data\)
• .chmidasrc in the current directory

The midasrc mechanism is similar to that in MidasPlus, where a file named .midasrc in the user's home directory was automatically executed upon program startup. In general, the same file can be used in Chimera after minor adjustments. The differences in atom specification mainly reflect additions, but note that in Chimera, chain IDs are specified differently and mainchain is not accepted as a specifier. A few Midas/MidasPlus commands are unsupported by Chimera.

Mouse button functions including the manipulation of models can be reassigned using the Mouse section of the Preferences dialog. Functions may be assigned to the left, middle, and right mouse buttons alone and and in combination with the Ctrl key. There can be no more than one function checked per row (per button or Ctrl-button). Mice with fewer than three buttons can be accommodated.

icon	meaning	default assignment		icon	meaning	default assignment
	rotation	1 (left button)			picking (selection from screen)	Ctrl-1
	XY-translation	2 (middle button)			Z-translation	Ctrl-2
	scaling	3 (right button)			lens control	Ctrl-3
	pop-up Chimera menu	(none) see alternatives

Continue rotation after mousing (true/false) indicates whether rotation should continue when the corresponding mouse button is released while the cursor is in motion.

The New Molecules section of the Preferences dialog controls how newly opened molecules will initially appear. See also: molecule model attributes, presets

• use new color for each model (true/false) - set the model-level color (see coloring hierarchy) differently for each new molecule model; submodels with the same main model number will be assigned the same model-level color. This preference can also be controlled with set/~set autocolor.
• otherwise, use color (a color well, by default showing a light gray color) - color at the model level, see coloring hierarchy
• ribbon display (off/on) - whether to show ribbon; ribbons are only drawn for proteins and nucleic acids. Protein helix and strand assignments are taken from the input structure file or generated with ksdssp.
• ribbon cross section (edged/flat/rounded/any additional styles created and named with the Ribbon Style Editor) - ribbon style (see also ribrepr)
• ribbon scaling (Chimera default/licorice/any additional scalings created and named with the Ribbon Style Editor) - ribbon scaling (see also ribscale)
• ribbon hides backbone atoms (true/false) - whether showing ribbon for residues within the model hides backbone atoms for those residues (see the command ribbackbone for details)
• line width (1.0 by default) - pixel width of lines depicting bonds (when in the wire draw mode)
• atom style (dot/ball/endcap/sphere) - atom draw mode (excluding monatomic ions)
• bond style (wire/stick) - bond draw mode
• monatomic ion style (dot/ball/endcap/sphere) - draw mode to use for monatomic ions
• stick scale (1.0 by default) - scale factor for bonds in the stick draw mode. The stick scale is multiplied by individual bond radii (default 0.2 angstroms) to generate stick radii in angstroms. Changing stick scale is preferable to changing all of the bond radii in a model, because the former will also scale singleton atoms in the endcap draw mode appropriately. Either way, the other endcap atoms (those participating in bonds) will be scaled to match the thickest of the attached bonds.
• ball scale (0.25 by default) - scale factor for atoms in the ball draw mode. The ball scale is multiplied by individual atom VDW radii to generate ball radii in angstroms.
• per-atom coloring (none/by element/by heteroatom) - whether to leave atom colors unassigned (none; atoms will inherit model colors) or to assign element colors to all atoms (by element) or only the non-carbon atoms (by heteroatom)
• auto-chaining (off/on) - whether to connect atoms that precede and follow undisplayed segments (whether to draw pseudobonds between them)
• metal complex line width (2.5 by default) - pixel width of pseudobonds depicting metal coordination (when in the wire draw mode)
• metal complex color (a color well, medium purple by default) - color to use for pseudobonds depicting metal coordination
• dash metal complex lines (true/false) - whether the pseudobonds depicting metal coordination should be shown as dashed (rather than solid) lines when in the wire draw mode

The New Surfaces section of the Preferences dialog sets parameters for newly created molecular surfaces. See also: molecular surface attributes, presets

• representation (solid/mesh/dots) - display type
• probe radius (1.4) - radius in Å of the probe sphere used to compute the surface. A larger probe decreases surface bumpiness because it fits into fewer crevices. A radius of 1.4 Å is commonly used to approximate a water molecule.
• vertex density (2.0) - vertices per Ų. Greater density results in a smoother surface but increases computational demands for calculating and moving the surface.
• line width (1.0) - pixel width of lines used in the mesh surface representation
• dot size (1.0) - pixel size of dots used in the dot surface representation
• show disjoint surfaces (true/false) - whether to check for multiple disjoint surfaces rather than assuming there is only one (increases calculation time)

The PDB section of the Preferences dialog includes:

• Fetch from web as necessary (true/false) - whether to retrieve a PDB file specified by PDB ID from the Protein Data Bank web site when it is not found in a local installation (see the Web Access preferences for proxy settings, if needed)
• Personal PDB directories - additional directories to look in for PDB files; a user may Add a directory to the list of places to look, or choose a previously added directory from the list and then Delete it from the list

The POV-Ray Options section of the Preferences dialog sets specifications for raytracing with POV-Ray.

• POV-Ray executable [ location ] - the location of the POV-Ray executable. This is filled in automatically for the executable included with Chimera, but another location could be specified.
• Show preview (true/false) - whether to show a preview; regardless of this setting, however, a preview will not be shown during movie recording or when Chimera is in nogui mode.
• Quality (default 9, range 0-11) - output image quality, adjusted by omitting calculations that are normally performed. For example, values < 4 yield images without shadows [quality details at the POV-Ray site].
• Antialias (true/false) - whether multiple samples should be averaged to produce a single output pixel; otherwise, POV-Ray will simply trace one ray per pixel. Analogous to (but independent of) Chimera image supersampling, this supersampling in POV-Ray smooths edges in output images [antialias details at the POV-Ray site].
• Antialias method (fixed/recursive) - how pixels should be supersampled when antialiasing is used. In the fixed method, POV-Ray initially traces one ray per pixel. Each pixel is compared to its neighbors to the left and above. If the colors of two pixels differ by more than the antialias threshold, each of the pixels will be subsampled according to the antialias depth (if the depth is 3, a grid of 3*3=9 samples will be taken per output pixel). In the recursive method, POV-Ray initially traces 4 rays at the corners of each pixel. Where the colors of adjacent samples differ by more than the threshold, subsamples will be taken and compared. This process is repeated until adjacent colors agree within the threshold, or the maximum number of subdivision cycles (the specified antialias depth) has been performed.
• Antialias depth (default 3, range 1-9) - meaning depends on which antialias method is used
• Antialias threshold (default 0.3, range 0.0-3.0) - two colors are compared by summing the absolute differences in their red, green, and blue components; differences greater than the threshold trigger further sampling when antialiasing is used. Lower threshold values increase the number of samples and the calculation time, whereas a threshold of 3.0 will suppress further sampling.
• Jitter (true/false) - whether to introduce noise by randomly wiggling the supersample locations when antialiasing is used [jitter details at the POV-Ray site]
• Jitter amount (default 1.0) - values are specified relative to 1.0, which is the most jitter that can be performed while retaining supersamples within the original pixel
• Output alpha channel (true/false) - whether to include transparency information for output pixels; including alpha makes areas of the image transparent where the background shows through [output alpha details at the POV-Ray site].
• Wait for POV-Ray to finish (true/false) - whether to prevent further commands from executing until POV-Ray has finished generating the image. During movie recording, the behavior will always be as if this were set to true.
• Keep POV-Ray input files (true/false) - in addition to an image, raytracing generates files for POV-Ray containing the scene (*.pov) and the raytracing options (*.ini); this setting indicates whether to keep or remove such files after image generation. During movie recording, the files will always be cleared.

The Preferences section of the Preferences dialog includes:

• Preferences file - the location of the preferences file for the current session
• Read-only - whether the preferences file for the current session should be treated as read-only. The initial setting reflects the file permissions at Chimera startup. When Read-only is false, Chimera may update the file with changes in preference settings and other information; switching to true prevents subsequent changes in the file. When Read-only is true, Chimera will not update the file; switching to false (if the file is already writable, or is owned by the user) will enable its modification by Chimera.
• All categories:
  • Restore to saved settings - replace the current settings in all categories with those previously saved in the preferences file
  • Reset to factory defaults - replace the current settings in all categories with the original defaults
  • Save - save the current settings in all categories to the preferences file

The Tools section of the Preferences dialog allows control over the following Settings for each entry in the Tools menu:

• Auto Start - whether to launch the tool automatically upon Chimera startup
• On Toolbar - whether to show the tool's icon in the toolbar
• In Favorites - whether to include the tool in the Favorites menu
• Confirm on Start - whether to ask for confirmation before starting the tool

The Web Access section of the Preferences dialog includes:

• Confirm open of commands or code (once per session/each time/never) - whether/how often to ask for confirmation before opening certain types of data linked to web pages.
• Accept web data (true/false) - whether the running instance of Chimera can be used as a helper application for data linked to web pages (and can receive files specified with chimera --send). On Mac OS X, this preference is not shown, but is effectively true unless Chimera was started from the terminal command line. A browser must be configured to send the files to Chimera. If there is no running instance of Chimera enabled to accept web data, another instance of Chimera will be started and used to open the data. If there are multiple running instances of Chimera set to accept web data, the file will be sent to the instance that most recently had focus (was most recently clicked into).
• Use HTTP proxy (true/false) - whether to use a proxy to connect to the internet through a firewall (for example, to fetch a PDB file from the Protein Data Bank web site); the server and port number settings (below) should generally be the same as those used for web browsers
• Proxy server - the hostname or IP address of the proxy server
• Proxy port - proxy port number to use