Tips for Multi-Resolution Delphi Applications

What to Keep in Mind When Scaling Delphi Apps on Different Screen Resolutions

When designing forms in Delphi, it's often useful to write the code so that your application (forms and all objects) looks essentially the same regardless of what the screen resolution is.

The first thing you want to remember early on in the form design stage is whether you're going to allow the form to be scaled or not. The advantage of not scaling is that nothing changes at runtime. The disadvantage of not scaling is that nothing changes at runtime (your form may be far too small or too large to read on some systems if it is not scaled).

If you're not going to scale the form, set Scaled to False. Otherwise, set the property to True. Also, set AutoScroll to False: the opposite would mean not changing the form's frame size at runtime, which doesn't look good when the form's contents do change size.

Other Things to Remember

Here are some other important things to remember about runtime resolution and system font size (small/large fonts):

  • Set the form's font to a scaleable TrueType font, like Arial. Only Arial will give you a font within a pixel of the desired height.
    Note: If the font used in an application is not installed on the target computer, then Windows will select an alternative font within the same font family to use instead.
  • Set the form's Position property to something other than poDesigned, which leaves the form where you left it at design time. This usually ends up way off to the left on a 1280x1024 screen—and completely off the 640x480 screen.
  • Don't crowd controls on the form—leave at least 4 pixels between controls so that a one pixel change in border locations (due to scaling) won't show up as overlapping controls.
  • For single line labels that are alLeft or alRight aligned, set AutoSize to True. Otherwise, set AutoSize to False.
  • Make sure there is enough blank space in a label component to allow for font width changes - a blank space that is 25% of the length of the current string display length is a little too much, but safe.
    Tip: You'll need at least 30% expansion space for string labels if you plan to translate your app into other languages. If AutoSize is False, make sure you actually set the label width appropriately. If AutoSize is True, make sure there is enough room for the label to grow on its own.
  • In multi-line, word-wrapped labels, leave at least one line of blank space at the bottom. You'll need this to catch the overflow when the text wraps differently when the font width changes with scaling. Don't assume that because you're using large fonts, you don't have to allow for text overflow—somebody else's large fonts may be larger than yours!
  • Be careful about opening a project in the IDE at different resolutions. The form's PixelsPerInch property will be modified as soon as the form is opened, and will be saved to the DFM if you save the project. It's best to test the app by running it standalone, and edit the form at only one resolution. Editing at varying resolutions and font sizes invites component drift and sizing problems. Make sure that you set your PixelsPerInch for all your forms to 120. It defaults to 96, which causes scaling problems at a lower resolution.
  • Speaking of component drift, don't rescale a form multiple times, at design time or a runtime. Each rescaling introduces round off errors which accumulate very quickly since coordinates are strictly integral. As fractional amounts are truncated off the control's origins and sizes with each successive rescaling, the controls will appear to creep northwest and get smaller. If you want to allow your users to rescale the form any number of times, start with a freshly loaded/created form before each scaling, so that scaling errors do not accumulate.
  • In general, it is not necessary to design forms at any particular resolution, but it is crucial that you review their appearance at 640x480 with large and small fonts, and at a high-resolution with small and large fonts, before releasing your app. This should be part of your regular system compatibility testing checklist.
  • Pay close attention to any components that are essentially single-line TMemos—things like TDBLookupCombo. The Windows multi-line edit control always shows only whole lines of text—if the control is too short for its font, a TMemo will show nothing at all (a TEdit will show clipped text). For such components, it's better to make them a few pixels too large than to be one pixel too small and not show any text at all.
  • Keep in mind that all scaling is proportional to the difference in the font height between runtime and design time, not the pixel resolution or screen size. Remember also that the origins of your controls will be changed when the form is scaled—you can't very well make components bigger without also moving them over a bit.

    Read on to find about properties like Align or [Anchors] that help you design the GUI.

    Anchors, Alignment and Constraints: Third party VCL

    Once you know what issues to bear in mind when scaling Delphi forms on different screen resolutions, you are ready for some coding.

    When working with Delphi version 4 or higher, several properties are designed to help us maintain the look and layout of controls on a form.

    Use Align to align a control to the top, bottom, left, or right of a form or panel and have it remain there even if the size of the form, panel, or component that contains the control, changes. When the parent is resized, an aligned control also resizes so that it continues to span the top, bottom, left, or right edge of the parent.

    Use Constraints to specify the minimum and maximum width and height of the control. When Constraints contains maximum or minimum values, the control can’t be resized to violate those constraints.

    Use Anchors to ensure that a control maintains its current position relative to an edge of its parent, even if the parent is resized. When its parent is resized, the control holds its position relative to the edges to which it is anchored. If a control is anchored to opposite edges of its parent, the control stretches when its parent is resized.

    procedure ScaleForm
        (F: TForm; ScreenWidth, ScreenHeight: LongInt) ;
    begin
       F.Scaled := True;
       F.AutoScroll := False;
       F.Position := poScreenCenter;
       F.Font.Name := 'Arial';
       if (Screen.Width <> ScreenWidth) then begin
         F.Height :=
             LongInt(F.Height) * LongInt(Screen.Height)
             div ScreenHeight;
         F.Width :=
             LongInt(F.Width) * LongInt(Screen.Width)
             div ScreenWidth;
         F.ScaleBy(Screen.Width,ScreenWidth) ;
       end;
    end;