<AWT Dev> RFR: 8266079: Lanai: AlphaComposite shows differences on Metal compared to OpenGL

[Alexey Ushakov]

On Wed, 26 May 2021 13:49:24 GMT, Alexey Ushakov <avu at openjdk.org> wrote:

> Set black color for underlying window background to perform correct blending operations in metal with window surface destination

Looks like the second option won't work because the result of blending will still be mixed with the NSWindow background color. Also, I tried several more approaches (Use only rgb blending, make the layer opaque). They helped to resolve the test issues but caused regressions in other areas (SwingSet2 tree for example). So, now I think that the only working solution is presented here (to set the background color of the window) 

> Yes, looks like we have the flashing problem back. It seems more serious than this particular bug.
> We have two options here:
> 
> 1. accept this behavior for metal (It would be not a problem if we implement  JDK-8265445)
> 2. reimplement all the composing operations via shaders instead of using metal blending rules

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PR: https://git.openjdk.java.net/jdk/pull/4206