RFR: JDK-8297449: Update JInternalFrame Metal Border code

[Alexey Ivanov]

On Wed, 23 Nov 2022 00:46:57 GMT, Harshitha Onkar <honkar at openjdk.org> wrote:

> Updated Metal Border code for JInternalFrame. 
> 
> - Added instanceof check before casting Graphics to G2D.
> - Replaced roundHalfDown with Region.clipRound()

Changes requested by aivanov (Reviewer).

src/java.desktop/share/classes/javax/swing/plaf/metal/MetalBorders.java line 253:

> 251:         public void paintBorder(Component c, Graphics g, int x, int y,
> 252:                                 int w, int h) {
> 253:             if (g instanceof Graphics2D) {

I think it's not the right approach. You should separate the parts of code into those which require `Graphics2D` (resetting transform, stroke width) and those which don't, so that the border is still painted even when `g` is not an instance of `Graphics2D`.

Take a look at how @alisenchung handled it for `EtchedBorder`:
https://github.com/openjdk/jdk/blob/b42c1ad1086a5c3f579e27380d23f67f8cebb437/src/java.desktop/share/classes/javax/swing/border/EtchedBorder.java#L159-L171

The border is still rendered even if the passed in `Graphics` is not `Graphics2D`.

-------------

PR: https://git.openjdk.org/jdk/pull/11305