RFR: 8287912: GTK L&F : Background of tree icons are red

[Prasanta Sadhukhan]

On Thu, 1 Sep 2022 06:27:17 GMT, Abhishek Kumar <duke at openjdk.org> wrote:

> The background of tree icons are not red in GTK LAF when setOpaque is set to false for tree component.
> It has been observed that while painting tree cell background in GTK LAF, a rectangular area is also painted with background color (white). 
> 
> Proposed solution is to check the opacity of tree component before drawing tree cell background. If the opacity is set to "false" then the background shouldn't be painted.
> 
> An automated test case has been added and checked in CI, link is added in JBS.

test/jdk/javax/swing/JTree/TestTreeBackgroundColor.java line 1:

> 1: 

remove this empty line

test/jdk/javax/swing/JTree/TestTreeBackgroundColor.java line 81:

> 79:                     if (c.equals(Color.RED)) {
> 80:                         passed = true;
> 81:                     }

better to check at midpoint tree.width/2, tree.height/2 and also break if it's RED, no need to check all pixels.

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PR: https://git.openjdk.org/jdk/pull/10112