scalable layouts : Java Glossary

PostScript

Problem Areas

• Fonts. Sizes are specified in non-scaling points/pixels.
• Images. *.png, *.gif images are specified in non-scaling pixels. *.jpg will scale.
• The sizes of Frames, Panels etc. are specified in non-scaling pixels.
• setSize, setLocation etc. are specified in non-scaling pixels.
• Layouts are in general not smart enough to do things like remove optional fields, remove labelling or shorten fields when the real-estate gets tight.
• There is no general way to query the user’s visual acuity to know the smallest point size the user can tolerate.
• There is nothing like the Microsoft dialog unit for the API to use that generates auto-scaling displays.
• Knowing the width of the physical screen in pixels and the width of the application window in pixels still gives only an approximation to the best point size/dialog unit to use.

Solutions

There are some techniques you can work with:

• Component-level scaling: use a Look & Feel like Substance or JGoodies Looks Plastic Look & Feel family or JGoodies Looks Windows Look & Feel that let you be very precise for the most popular resolutions between 80dpi and 140dpi.
• Since the dialog font scales with the resolution and the desktop font setting, if any, you may want to look for a Swing Look & Feel that honors these two settings, e.g. Substance, Plastic and the JGoodies Windows.
• JLabel, JTextField and JTextArea will scale correctly because they are defined by the number of characters displayed.
• JComboBox and JList have prototype values that are used to determine the width and height and thus will automatically scale too.
• MigLayout and JGoodies FormLayout provide conversions from scalable units to pixels, so you can define sizes, gaps, and borders in a resolution-independent way. You can avoid using physical pixel units for screen positions, widths and heights.
• Microsoft Windows uses Dialog Units (DLU) for precise resolution-independence. On Windows, a button should have a minimum width of 50 dlu. And the width of a JTree in a JScrollPane should be defined by its content or in a resolution-independent way, often in dlu.

Tools

import java.awt.Dimension;
import java.awt.Toolkit;

...

// Get screen size in pixels, width by height.
Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();

// Get screen resolution in dots per inch.
// The Americans who develop Java have not noticed the world has gone metric.
int dpi = Toolkit.getDefaultToolkit().getScreenResolution();

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