RFR: 8258754: Gracefully fallback to the OpenGL rendering pipeline if Metal rendering pipeline initialization fails [v5]

[Ajit Ghaisas]

On Fri, 8 Jan 2021 20:59:49 GMT, Phil Race <prr at openjdk.org> wrote:

> this implies that -Dsun.java2d.opengl=false on its own means the same as -Dsun.java2d.metal=true.
> 
> This is a bit grayer. It would imply that there is a designated fall back.
> 
> I take that back - it isn't grey. Because the default for metal is false, it means you've disabled both so rule 1 applies
> I'll add another rule up above to make it clearer.
> 
> But .. we have a sort of precedent on windows that d3d=false means fall back to gdi. So that contradicts the above :-(
> 
> So is metal a "fallback" or an "option" ? We don't fall back to optional pipelines. Meaning d3d=false would not cause opengl to be used on windows.

My thinking differs on this. When we will integrate Lanai JEP to the mainline, we will have 2 rendering pipelines on macOS - OpenGL and Metal - OpenGL being default.
If user specifically asks for -Dsun.java2d.opengl=false, then we should definitely try to use the other available pipeline - whether it is fallback or optional is immaterial. Otherwise, we would end up in a situation where no UI will be launched.

I suggest that we deliberate and decide on this outside of this PR.

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PR: https://git.openjdk.java.net/lanai/pull/147