GUI design guidelines

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These guidelines apply to the Lazarus IDE but may be used for other projects as well.


All dialogs and windows must not use fixed sizes. Keep in mind that font sizes and translated captions can vary. Use splitters and panels.

All forms and dialogs must work on a screen of 800x600 or higher resolution.

Dialogs (modal forms)

Dialogs are special forms that need the user to make / change some setting before lazarus can continue.

  • Close on Escape (if the key is not used otherwise)
  • Define default button and Return activates it (if the key is not used)
  • If it has scrollable content (e.g. contains a TMemo, TListBox, TTreeView) it should be resizable and size is stored

Dialog Settings

Settings that should be applied in general are:

  • BorderStyle :
    • bsSizeable - if the dialog is complex and resizing is really needed.
    • bsDialog - if dialog is simple and resizing is not needed (NOTE: all dialogs should remain resizable internally because of localization issues).
  • Position : poScreenCenter.
  • FormStyle : Do not use fsStayOnTop, as this can be pretty annoying under some window managers.
  • BorderIcons:
    • [biSystemMenu] - for modal shown dialogs
    • [biSystemMenu,biMinimize,biMaximize] - for non-modal shown dialogs

General layout

  • On the bottom of the form Button panel should be placed.
  • Close on Escape (if key not used otherwise).
  • Define default button and Return activates it (if key not used).
  • Avoid using long captions on buttons. Use Hint property to explain button action in details.
  • The size of resizable dialogs should be saved and restored next time the dialog will be opened.
  • All hints and captions used on a form should be as resourcestring, so localization can be applied.

Spacings and sizes

  • Dialogs must be designed to work independently of resolution and font height.
  • Spacing between elements: 6 pixels.
  • Do not set maximum constraints.
  • Do not set minimum height of regular buttons.
  • You can set a minimum width of 90 for buttons.
  • AutoSize property need to be set for buttons, labels, ... to properly display localized text if it is longer than expected.
  • All buttons in a group (including buttons that contain glyphs) must have the same width and height. Use a TPanel and set the Align and BorderSpacing properties.

Button panel

The button panel should consist at least of the following elements:

  • OK button.
  • Cancel button.
  • Next button (optional).
  • Previous button (optional).
  • Help button.


To make sure that a dialog after resizing will keep on showing the components in a good way, anchoring is being used. Each components has a property called Anchors. With this property you can determine the way a component is anchored to it's parent.

Hint: Use the anchor editor of the IDE.


Another way to organise components is using alignment. Each component has a property Align. By selecting the appropriate align position several components can be positioned properly.


Especially useful in combination with Align is the BorderSpacing property. (Also found on the Anchors dialog). A typical borderspacing of 6 pixels around a component is used.

See also