Slicer3:Human Interface and Style Guide for Developers

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Slicer Human Interface Design and Style Guidelines

Introduction

3D Slicer (or Slicer) is a large and continuously developing application. Its base is designed to offer substantial core functionality, and its modules extend that functionality to include specialized and cutting-edge research tools and interoperability with other open source softwares. The development effort seeks to simultaneously ensure that:

  • Slicer meets the needs of a broad user community,
  • developers can easily contribute to and extend the application,
  • the software remains easy to test and maintain, and
  • the appearance and behavior of Slicer's interface are easy to learn & use, and aesthetically pleasing.

These human interface design and style guidelines are a resource to help Slicer developers to create module interfaces that are easy to learn, understandable and usable, and that conform to Slicer’s general appearance and behavior conventions. The recommendations in this document are designed to be easy for developers to apply and their adoption is strongly encouraged. However, a developer’s interface design can depart from convention when these guidelines appear inappropriate for a particular application.

The guidelines are intended for software developers, interface designers, and graphic artists who will be creating core functionality or software modules for 3D Slicer. Included design recommendations are based broadly on cognitive science, human perception, human factors and HCI. Included is information on basic interface components, choosing and using them effectively and in a manner consistent with Slicer conventions.

Organization

This document is organized into the following two sections:

1. Slicer Design Principles

2. Slicer Widget and Interface Style Specifics

Within these sections, developers will find recommendations that promote usable and consistent Slicer module interfaces, and link to technical resources where appropriate.


Slicer Design Principles

Design for scientists and engineers

Remember that design is not just about appearance and style; it's about communicating ideas and solving problems.

Most users of the software you develop for Slicer will be from one (or more) of these communities:


  • Algorithm researchers (who work within Slicer's development environment and with associated toolkits)
  • Biomedical engineers (who rely on Slicer's interactive enironment and scripting capabilities)
  • Application scientists (who use Slicer as a desktop application and turnkey system)


In general, these categories of users will not want appearance and style to get in the way of the task they want to accomplish. Interfaces should have a well-organized, accessible, simple and clean design that:


  • exposes essential features,
  • provides access to essential information,
  • permits tasks to be accomplished efficiently and reliably,
  • provides adequate feedback, and
  • is forgiving of mistakes.


Accessibility & appropriateness

Currently, Slicer has neither an accessibility component in the design & engineering effort, nor a program to internationalize or localize its interface. However, because keeping Slicer usable and appropriate for a large and diverse user base is important, developers are encouraged to design interfaces that are appropriate for users with disabilities and for users from multicultural, multinational, or multilingual backgrounds.

In the absence of formal engineering infrastructure to support a principled approach, Slicer is not yet compatible with sensory assistive technologies. In addition, Slicer relies on the English-language keyboard character set, uses hard-coded strings and concatenated strings (which Tcl makes particularly easy), a left-to-right convention for reading/writing that manifests in layout, no number and date formatting, and so on. Until formal approaches to both accessibility and internationalization are implemented, the following informal design recommendations are offered:

  • Make sure your language (what you call things and how you phrase things) is appropriate,
  • Try to make sure your graphics aren't overloaded with meaning you don't intend,
  • Make sure all widgets (especially icons) have explanatory labels or pop-up balloon help text,
  • Provide keyboard access for important functionality in a manner consistent with Slicer's conventions,
  • Try not to override the font specification in Slicer's theme, which users can adjust (somewhat) to fit their preference,
  • Use the Application Settings infrastructure to save user preferences where it makes sense,
  • Minimize physical and mental stress of performing repetitive actions,
  • Provide prompting and feedback for all actions.

Following these general suggestions will improve the usability of your interface for all users.

Design for varying levels of expertise

Slicer users can be classified into three broad bins: novice, intermediate and expert users. Each type of users will desire a different user experience, and would like to use the interface to your module's functionality in a different way. Ideally, an interface will support the needs of all three types alike.

  • Novice users: Novice users will likely rely heavily on the GUI widgets, their pop-up balloon help (which should include any available keyboard hot-keys), and external sources of information like tutorials or documentation. Novice users may work at a relatively slow pace, since they are both exploring the scope of functionality provided, and learning how to use it.
  • Intermediate users:
  • Expert users:

Keep it simple

Use clarifying layouts

Keep it stable

Keep users informed

Allow users to correct mistakes

Respect users' wishes (application settings)

Maintain consistency with Slicer's appearance and behavior

Make principled design decisions

Follow Slicer's User-Centered Design Practice

Slicer's light-weight User-Centered Design Practice document is a resource to help developers take a human-centered approach in an open source development effort (in which interface & information designers and usability experts are not often part of the team.) Using this design approach offers the following benefits:


  • Users will learn to use your module faster, because its interface will be understandable and interface elements will look and behave in an expected manner.
  • Users will be able to accomplish their tasks by following an appropriate and satisfying workflow, or a curiosity-driven exploration, at an appropriate pace.
  • Your module will be accessible to users at all levels of expertise (novice, intermediate and advanced).
  • Your module will have a nice look & feel that fits within the 3D Slicer environment.


Modules that hit these marks should maximize the reach of a developer’s research, design, and programming effort, offer contributing agencies, institutions, and individuals the maximum impact for their investment, and provide the user community with cutting-edge functionality that they find satisfying to use. The Slicer community ultimately leaves the choice about design and implementation process to contributing developers, and the recommendations in this document are not enforced. Since we believe that incorporating user-centered design will improve Slicer overall, developers are strongly encouraged to adopt this light-weight and flexible practice, and adapt it to fit their environment and project timeline.

Slicer Interface Design & Style Information

Overall Look and Feel

GUI Style: Try not to add style elements (like foreground and background color, font, relief, etc.) to the interface you create; let the options database (as set up by the vtkSlicerTheme class) specify the style for the widgets in your module so that all modules appear consistent within the Slicer3 application.

Module style

Collapsing frame style

Tabbed notebook style

Application windows

Types of windows

Window appearance

Message windows & dialogs

Other pop-up windows

Menu bar and its menus

What goes in the File Menu

What goes in the Edit Menu

What goes in the View Menu

What goes in the Help Menu

Application settings

Confirm on delete

Check vtkSlicerApplication::ConfirmDelete setting; if a user has requested to be presented with a confirm on delete, then give them that option.

Adding your own application setting options

Mouse modes

Mouse modes are currently in transition in Slicer3 Beta. Mode-free design is ideal. Modes are required to disambiguate what a mouse click means in Slicer's 3D Viewer and Slice Viewers.

Basic mouse modes

Adding new mouse modes

Mouse cursors

Basic mouse cursors

Defining your own mouse cursors

Keyboard shortcuts

Keyboard shortcut paradigm

Basic keyboard shortcuts

Defining your own keyboard shortcuts

Event Bindings

With respect to the specification of keyboard accelerators, please follow these three recommendations;

  • Before assigning "hot-keys" to functionality, either in the main Slicer application or in a new module, please consult the Slicer3 event bindings table (and design plan) to make sure the key is not already assigned.
  • Across Slicer modules, try to use similar "hot-key" assignments for similar functionality; this consistency makes Slicer easier to learn.
  • Once you assign "hot-keys" in your module, please add those mappings to the Slicer3 event binings table for others to reference.

Application Font

Verdana is the font chosen for the 3DSlicer brand.

Maintaining consistency of type is an important component of maintaining a coherent look and feel for 3DSlicer and any related or derived visual communications. Verdana was designed specifically to be read on a digital display; it is recommended that we use Verdana (or Geneva) wherever possible in 3DSlicer's web presence and online tutorial materials, and wherever reasonable and appropriate in formal printed materials.

Within the software, since it can't be guaranteed that these fonts will be widely available on all platforms, Helvetica or Arial should be used as a substitute. Slicer's theme sets the application font to be Helvetica 8 normal. Please avoid typefaces with serifs.

Icons

Icons can be a powerful way to represent complicated information within a small footprint on the GUI panel. They associate a visual image with data, state, or a particular operation.

  • They should be easy to parse, convey a strong metaphor, and not require significant time for a user to interpret.
  • They should be memorable so that a user can recognize them quickly in future sessions with your module.
  • If an icon already exists within 3DSlicer to represent the data, state or operation you want to indicate, then re-use that icon (indicate visibility with the open/shutting eye, for example.)
  • Note: if the concept is too difficult to represent with a picture, then a text label can always be used instead!

When designing icons, do bear in mind that it's possible to offend users with images that have cultural or polictal connotations. Even colors can have connotations for users in different parts of the world that may be surprising and unintended for the designer and developer. Generally speaking, it's useful to avoid images that contain:

  • icons that depict only hands or feet
  • images of animals
  • maps containing disputed boundaries or region names.
  • lists of countries that are not in alphabetical order.
  • pictures of flags
  • pictures of money

Slicer icon conventions

These icon blanks are provided for download and use:

  • Enabled or Enabled+Selected: conventional Slicer icon
  • Disabled or Enabled+Deselected: "deselected" Slicer icon
  • Enabled Menubutton: conventional Slicer menubutton icon
  • Disabled Menubutton: "disabled" Slicer menubutton icon
Icons as Buttons & MenuButtons
Icons inside Menus

3DSlicer icons should all be of dimension 21x21 pixels.

Enabled or Enabled + Selected icons should have:

  • a white background (r=255, g=255, b=255, or #FF FF FF)
  • a black hairline along the perimeter (r=0,g=0,b=0, or #00 00 00).

Disabled or Enabled + Deselected icons should have:

  • a grey background, value (r=230, g=230, b=230, or hex value #E6 E6 E6)
  • a grey hairline perimeter of value (r=178, g=178, b=178, hex value #B2 B2 B2).

Icons currently used in Slicer's Base

Below is a figure of icons currently in use in 3DSlicer. If the icon you need is already used in Slicer, we encourage its re-use in your own module (the visibility icon is a good example). However, if an icon is re-used, make sure you are using it to convey the same meaning/function -- icons shouldn't have different meanings in different places. Finally, make sure any new icons designed for a module don't duplicate ones already in use elsewhere in Slicer.

Slicer icons


Widget-specific conventions

Buttons & Pop-up Buttons

PushButtons
PushButtons with icons
Representing state with toggling icons
ChangeColorButtons & Color Selector Widgets
HelpButtons

Widgets for Selecting things

Using selection widgets effectively
MenuButtons
MenuButtons with icons
Menus & menu behavior
Menuitems
Cascades
Context menus
Checkbuttons and Radiobuttons
Checkbuttons and Radiobuttons with icons
Entry Widgets
Listboxes
Multi-column Lists
SpinBoxes and SpinButtons

Widgets for Adjusting things

Choosing the best widget for the task
Sliders
Range Widgets

Widgets for Displaying things

Choosing the widgets for the task
Labels
Tree Widgets
Text Widgets
Toolbars & Toolbar Sets
Progress Feedback

Widgets for Editing things

When to use an editor widget
Color Transfer Function Editor
Parameter Value Function Editor
Piecewise Function Editor
Text Property Editor

Widgets for Containing things

Organizing your GUI panel
Frames and SplitFrames
Pop-up Frames
Notebooks
FileBrowsers and FileBrowserDialogs
Canvas Widgets

Groups of Widgets

Slicer Widgets

Available Slicer widgets

Designing your own widgets

Layout Examples

Providing Help

Language

Credit and Logos

Progress Feedback

Colors: application palettes

Currently being modified... The Slicer3 color palettes are shown below. Developers of code, web content and training materials are encouraged to make color choices for GUI components according to this palette, bearing in mind that some of the colors are linked with special meaning, such as error (errorRed), warning (warningYellow), and system (systemBlue) messages.


main palette

name show me R G B hex use in slicer
Black 0 0 0 #000000 official text on enabled widgets
White 255 255 255 #ffffff official GUI background
LightestGrey 229 229 255 #e5e5ff theme uses this for mock 'drop shadow' around GUI panels
LighterGrey 223 221 226 #dfdde2 module collapsing frame title background
LightGrey 174 174 174 #aeaeae slices controller & slice viewer icon background; outlines around deselected Slicer checkbuttons and radiobuttons (and indicators)
MediumGrey 153 153 153 #999999 widget groove color, disabled widget text color
DarkGrey 82 82 82 #525252 low value grey for use in icons
DarkOchre 181 100 21 #b56415
MediumOchre 228 166 32 #e4a620
BrightOchre 243 172 34 #f3ac22
SliceYellow 237 213 76 #edd54c" yellow slice viewer color-code
LightOchre 244 233 127 #f4e97f
DarkOrange 194 74 24 #c24a18
MediumOrange 225 112 18 #e17012
BrightOrange 244 130 20 #f48214
LightOrange 243 184 70 #f3b846
LightestOrange 239 213 128 #efd580
DarkBrown 131 102 72 #836648
MediumBrown 193 115 79 #c1734f
Brown 190 148 98 #be9462
LightBrown 224 194 158 #e0c29e
LightestBrown 241 224 208 #f1e0d0
DarkRed 195 46 16 #c32e10
MediumRed 217 37 18 #d92512 fiducial symbol color in icons
SliceRed 243 74 51 #f34a33 red slice viewer color-code
LightRed 228 106 68 #e46a44
LightestRed 230 132 100 #e68464
DarkGreyGreen 70 84 48 #465430
MediumGreyGreen 103 142 63 #678e3f
SliceGreen 110 176 75 #6eb04b green slice viewer color-code
LightGreyGreen 138 165 112 #8aa570
LightestGreyGreen 202 230 181 #cae6b5
DarkGreen 37 86 57 #255639
MediumGreen 0 127 9 #007f09
Green 47 164 47 #2fa42f
LightGreen 89 198 122 #59c67a
LightestGreen 206 238 216 #ceeed8
DarkGreyBlue 72 64 101 #484065
MediumGreyBlue 99 92 133 #635c85
GreyBlue 116 143 173 #748fad
SlicerBlue 179 179 231 #b3b387 classic slicer 3D viewer background
LightGreyBlue 208 208 241 #d0d0f1 3D viewer icon background
DarkBlue 38 59 139 #263b8b
MediumBlue 56 95 177 #385fb1 mouse mode icon arrow color
Blue 42 113 187 #2a71bb
LightBlue 122 157 194 #7a9dc2
LightestBlue 152 212 213 #98d4d5


message palette:

name show me R G B hex use in slicer
ErrorRed 255 0 0 #ff0000 error message/dialog accent
SystemBlue 15 102 192 #0f66c0 message/dialog accent
WarningYellow 255 226 30 #ffe21e warning message/dialog accent


accent palette:

name show me R G B hex use in slicer
Magenta 255 0 255 #ff00ff 3D viewer cube & icon accent
Purple 191 73 190 #bf49be icon accent
DarkPurple 139 39 133 #8b2785 icon accent
LogoGreyBlue 113 127 152 #717f98 logo color & icon accent
IGTGrey 68 69 91 #44455b logo color & icon accent
LogoDarkGrey 48 56 60 #30383c logo color & icon accent
LogoLightYellow 240 217 138 #f0d98a logo color & icon accent
LogoMediumYellow 248 191 37 #f8bf25 logo color & icon accent
LogoOrange 240 108 46 #f06c2e logo color & icon accent
LogoRed 247 45 30 #f72d1e logo color & icon accent
NAMICBlue 0 99 181 #0063b5 logo color & icon accent
SPLGreen 0 153 102 #009966 logo color & icon accent

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