2. HIG (Human Interface Guidelines)
In order for all graphical user interface elements to appear consistent and to all the user to instinctively use dialogs, it is important that the following guidelines are followed in layout and design of GUIs.
Group related elements using group boxes: Try to identify elements that can be grouped together and then use group boxes with a label to identify the topic of that group. Avoid using group boxes with only a single widget / item inside.
Capitalise first letter only in labels, tool tips, descriptive text, and other non-heading or title text: These should be written as a phrase with leading capital letter, and all remaining words written with lower case first letters, unless they are nouns
Capitalize all words in Titles (group box, tab, list view columns, and so on), Functions (menu items, buttons), and other selectable items (combobox items, listbox items, tree list items, and so on): Capitalize all words, except prepositions that are shorter than five letters (for example, 'with' but 'Without'), conjunctions (for example, and, or, but), and articles (a, an, the). However, always capitalize the first and last word.
Do not end labels for widgets or group boxes with a colon: Adding a colon causes visual noise and does not impart additional meaning, so don't use them. An exception to this rule is when you have two labels next to each other e.g.: Label1 Plugin (Path:) Label2 [/path/to/plugins]
Keep harmful actions away from harmless ones: If you have actions for 'delete', 'remove' etc, try to impose adequate space between the harmful action and innocuous actions so that the users is less likely to inadvertently click on the harmful action.
Always use a QButtonBox for 'OK', 'Cancel' etc buttons: Using a button box will ensure that the order of 'OK' and 'Cancel' etc, buttons is consistent with the operating system / locale / desktop environment that the user is using.
Tabs should not be nested. If you use tabs, follow the style of the tabs used in QgsVectorLayerProperties / QgsProjectProperties etc. i.e. tabs at top with icons at 22x22.
Widget stacks should be avoided if at all possible. They cause problems with layouts and inexplicable (to the user) resizing of dialogs to accommodate widgets that are not visible.
Try to avoid technical terms and rather use a laymans equivalent e.g. use the word 'Opacity' rather than 'Alpha Channel' (contrived example), 'Text' instead of 'String' and so on.
Use consistent iconography. If you need an icon or icon elements, please contact Robert Szczepanek on the mailing list for assistance.
Place long lists of widgets into scroll boxes. No dialog should exceed 580 pixels in height and 1000 pixels in width.
Separate advanced options from basic ones. Novice users should be able to quickly access the items needed for basic activities without needing to concern themselves with complexity of advanced features. Advanced features should either be located below a dividing line, or placed onto a separate tab.
Don't add options for the sake of having lots of options. Strive to keep the user interface minimalistic and use sensible defaults.
If clicking a button will spawn a new dialog, an ellipsis char (…) should be suffixed to the button text. Note, make sure to use the U+2026 Horizontal Ellipsis char instead of three periods.