The first part of this series showed that it takes a little more than vector-based painting to make a look-and-feel resolution-independent. That part discussed two of the basic building blocks of high DPI support – alignment and baseline. This part is going to talk about borders.
Going back to my original post on high DPI support in look-and-feels, here is a screenshot of an internal frame under Vista configured with 144DPI (150% original setting):
While the visual elements appear properly scaled (fonts, check marks, title pane icons, scroll bars), the borders are not; all the borders in this screenshot are still 1 pixel wide. While it appears OK in this screenshot (since most of the monitors are still running on 100′ish DPI settings), the borders will almost disappear under a monitor that has 144DPI as the default setting. Here is a screenshot with correctly computed border widths:
As you can see, all the borders are properly scaled, including buttons, tabs, scroll bar, text field, combobox, combobox arrow button and checkmarks of checkboxes and radio buttons.
In addition to computing border widths under high DPI settings, there are two additional points to keep in mind. The first one is that the border insets must match the border width. You can no longer return Insets(1,1,1,1) from getBorderInsets() method when the border itself is painted with more than one pixel. The second one is that under larger widths, you need to change the painting bounds of the border itself. Here is a screenshot of a checkbox menu item with the checkbox border painted at (0,0):
As you can see, since the border width is three pixels, the outer border rims are clipped (since the border painting itself is clipped to the component bounds). In order to properly paint such a border, you need to offset it to half its width:
This offsetting also affects the border insets, which now should be at least border width and not half border width.
The next entry is going to talk about additional issues that are specific to the support of high DPI settings.