focusWidth isn't being properly taken into account for component size or painting

[gtimbo]

I'm loving FlatLaf, having only recently discovered it, but I'm having some painting issues when using the IntelliJ theme, which has a focusWidth of 2.0.

When I place various components (JButtons, JSpinners, etc) into a panel with no insets (using MigLayout("ins 0")), the outer border of the components is not being fully drawn. For example:

I'm on Windows 10, AdoptOpenJDK 11, using FlatLaf 1.1.2.

Here's an SSCCE that shows the issue:

import javax.swing.*;
import com.formdev.flatlaf.FlatIntelliJLaf;
import net.miginfocom.swing.MigLayout;
import static javax.swing.WindowConstants.EXIT_ON_CLOSE;

public class FocusWidthTest
{
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            try {
                UIManager.setLookAndFeel(new FlatIntelliJLaf());

                JFrame frame = new JFrame("Focus Width Test");
                frame.setLayout(new MigLayout("ins 0"));
                frame.add(new JButton("Test Button"));
                frame.pack();
                frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
                frame.setVisible(true);
            } catch (Exception x) {
            }
        });
    }
}

I haven't looked into the code too much, sorry, hence I'm not sure if it's a problem with the preferred size being incorrect, or with the painting not being offset correctly.

[DevCharly]

This is normal behavior. It is a feature of MigLayout called "visual padding".

FlatLaf tells MigLayout (via client property) the insets of the "invisible" space around a component (e.g. the focus border in IntelliJ/Darcula themes) and MigLayout then ignores the invisible space while computing its grid layout.

Following screenshot shows "FlatLaf IntelliJ" theme on left side (with focusWidth = 2)
and "FlatLaf Light" theme on right side (with focusWidth = 0).
Red rectangles indicate component sizes, green lines indicate grid rows.
Although buttons in IntelliJ theme are larger than in Light theme (because of the focus border),
the layout is the same and the (visual) gap between the (unfocused) buttons is the same.

With the help of MigLayout "visual paddings", the layout in the FlatLaf Demo stays stable when you switch from IntelliJ to Light theme:

Generally this is a great feature, but it has the problem that MigLayout places the component partly outside of its container if the container does not have insets.

IMHO MigLayout should take this into account and avoid placing components partly outside of container.
I consider creating a PR to improve this in MigLayout.

To fix this either use insets for the container:

frame.setLayout(new MigLayout("insets 2"));

or disable visual padding for the container:

frame.setLayout(new MigLayout(" novisualpadding, insets 0"));

See: https://www.formdev.com/jformdesigner/doc/layouts/miglayout-whitepaper/#layout_cons_novisualpadding

[gtimbo]

Thanks very much Karl, especially for going to so much effort in your reply! I've never had to deal with visual padding before in MigLayout, but that makes sense.

It does surprise me that MigLayout is able to essentially place components outside of their container -- although I do see how it makes the layout stable between LnF changes. A PR to improve MigLayout would probably help to ease confusion for other users.

I'll just use insets for now.