Webgl: Support allowTransparency option

[Tyriar]

Webgl addon added in #1790

I'm not sure what the state of this is currently.

[Eugeny]

Any updates on this one? This and character joiner support are the only things keeping me from using the WebGL renderer as default in Terminus.

[Tyriar]

No updates, needs someone to look into it until I get time to invest into bringing it to vscode.

[Tyriar]

Transparency seems to mostly work in from ef05a6a in #2560:

(term.setOption('theme', { background: '#ff000050' }))
The scrollbar seems a bit off though and haven't tested very thoroughly.

[Tyriar]

I tried to not draw a background rectangle at all as some colors ended up being off. There are two options for whoever wants too look into this in the future:

• Explore not using a background color for the viewport (would be inconsistent with other renderers)
• Explore not using a completely transparent background for webgl renderer (little worried about regressions here)

[Eugeny]

Works perfectly for me, including the scrollbar!

[Tyriar]

@Eugeny oh? The screenshot above of the demo is showing that the alpha color isn't correct as it's drawn twice (once in .xterm-viewport, once in canvas).

[Eugeny]

@Tyriar my primary concern was being able to have a completely transparent background - even in the current state transparent being drawn twice results in a usable transparent webgl xterm :)

[Tyriar]

@Eugeny ah ok, good 😃 I'll keep this open until the background color is correct though.

[Tyriar]

I believe the background color problem is fixed, notice how the right of the row is the same color:

There have also been several fixes that have gone in for v5. Let's close this off and track individual issues as they come up as this one's a little ambiguous what's left to do.