Java / Swing how to deal with different screen DPI and density settings?

Question

Hi everyone I've recently come across the problem that now days some monitors have different DPI settings, some monitors are much more dense such as, for example, Apple's Retina displays.

How would one compensate for the different DPI settings and densities on various monitors with Java? Is it possible to scale the controls to be the same size on any monitor. I know when programming for Android all measurements are in "DP" and you can specify different images for three different display densities.

Is there a way I could choose different images using Java / Swing for different display densities so my application doesn't look blurry on higher density monitors? Or is this not that important or possible? I know Chrome currently doesn't take into account DPI but Internet Explorer and other apps do.

Thank you for your help, I'm a long time Java developer I've just never thought about DPI before and was wondering how I might go about it :)

Answer 1

First, trust the platform's Look & Feel designers to choose sensible default sizes for text and controls. Then, avoid the temptation to frustrate those defaults. Here are some heuristics:

• Use layouts; when contemplating absolute positioning, consider a custom layout.

• Respect the preferred size of components.

• Avoid non-resizable components.

• In animation, scale graphics to the size of the enclosing Window.

• Test across a range of platforms, using emulation as required.

Answer 2

First thanks trashgod for the useful links you provided for they were very helpful.

Below I have listed some specifics on how to deal with issues concerning DPI changes that I have run into.

Font Issues:

If the font is not fitting in the component then look at Component Sizing Issues below for often the component is not sizing to what is inside. Otherwise in a JLabel you can apply HTML tags to automatically line wrap the text (there are other solutions but this works for me).

If the component's text is naturally the default font, size, and style (Tahoma 11 plain) then everything is automatically done for you. Know that user574171 gave pictures showing different font and layout managers issues and strengths in his link to http://kynosarges.org/GuiDpiScaling.html in his answer to How to set the DPI of Java Swing apps on Windows/Linux?. This question here is asking about the "Swing" issues but his link is useful in also comparing WPF, JavaFX, and Swing layouts with a basic components and different fonts. You can see there the "Swing a" font is the best, that is Tahoma 11 Plain. However it only works if the component is naturally the default font, size, and style (Tahoma 11 Plain). This means bolding, underlining, sizing, and a different font for the text will throw off the auto sizing for different DPI.

If the text is the default font (Tahoma) but bolded, underlined, or a different size then the text does not scale for different DPI's. To fix the scaling for different DPI's then check the box labeled "Derive the font from the default font." The "Relative" option will take the default DPI scaling font and apply your relative changes such as bigger or smaller, bold, and underlined. Also know that if the component is a JLabel then DPI scaling is automatic using HTML tags despite how you format the text (line wraps too).

If the component is not naturally the default font, style, and size (Tahoma 11 plain) or you want a different font (ie not Tahoma) then you need to associate the changes in another component that is naturally the default like a JLabel. Therefore if 125 DPI increases the font by 3 then you increase your desired font by the same.

Component Sizing Issues:

All components have a preferred, minimum, and maximum size properties but I have found that they do not play well with DPI changes. The "Respect the preferred size of components" bullet in trashgod's answer tells you all about it. To summarize let the default size of the component take care of itself for it will try to size to whatever is inside.

If the component can use the default sizes then DPI handling can be done for you. Just as trashgod's said "First, trust the platform's Look & Feel designers to choose sensible default sizes for text and controls. Then, avoid the temptation to frustrate those defaults." Again, the component of the default size usually sizes to what is inside (or acts re-sizable). From my own experience when I set re-sizable components I do it via "Horizontal Resizable" or "Vertical Resizable" for I have found it works very well with DPI changes as well as window resizing.

If the default size does of the component does not work then first try looking below at some specific issues I found. Alternatively try scaling the component according to changes in a component that does get scaled right. IE, apply ratio of what you expected the scaling component to be at 100% DPI and the change to the new DPI. Examples of components that need to be scaled to other component changes would be one that it's text is filled by code or it is an image.

As a last resort use a JScrollPane to allow the user to scroll to see the whole thing. If the window/dialog is fairly large then a JScrollPane is a great idea because if the DPI is higher for the user's eyesight then the window often is bigger than the screen.

Note: I have found that encapsulating groups of components in a JPanel helps swing handle DPI changes a lot better.

JTextField Size Issues:

Set the columns property and nothing else but the text if you wish. The columns property is the number of letters or numbers you want to show. Typically used when allowing the user to enter a number. Know that the columns property works great for multiple platforms.

JSpinner Size Issues:

Set the model to be accurate, valid, and default values. Therefore the auto-sizing of the component is done for the max value and works great for DPI changes and other platforms.

Table Row Height Issue:

Table row height does not change with higher DPI. I encountered this issue and it seems to be due to me trying to be compatible with older versions of Java. To fix multiply the change in font size ratio or change in JLabel height ratio due to the DPI change.