[Qtwebengine] Different ways of forcing software rendering

[Alexandru Croitor]

Hi,

--disable-gpu will disable GPU rendering on the Chromium side, and instead will use software rendering via the Skia library that is part of chromium.
Skia will write to bitmap images, and those will still be composited to the final widget / quick item using the Qt Quick Scene Graph,  which by default uses OpenGL. The option is enabled by default on Windows when ANGLE is used.

Afaik QT_QUICK_BACKEND = software will enable the use of a custom Qt software renderer for anything that uses the Qt Quick Scene Graph (instead of using GL).

I'm not sure about the other ones, but I guess they might force the usage of a software implementation of GL (Mesa e.g.).

> On 27. Jan 2018, at 12:29, Florian Bruhin <me at the-compiler.org> wrote:
> 
> Hey,
> 
> as far as I'm aware, there are various ways to force software rendering
> in QtWebEngine, and I was wondering what the difference between them is:
> 
> - Setting LIBGL_ALWAYS_SOFTWARE=1, which I think also affects
>  subprocesses spawned from Qt.
> 
> - Setting QT_XCB_FORCE_SOFTWARE_OPENGL=1, which AFAIK is equivalent but
>  doesn't affect subprocesses.
> 
> - Starting with --disable-gpu - is that the same?
> 
> - Setting QT_QUICK_BACKEND="software" - I think I read somewhere that
>  this does even more stuff via software rendering?
> 
> Would be great to have a quick overview there. I know some people with
> graphic (usually driver) issues where QT_XCB_FORCE_SOFTWARE_OPENGL=1
> doesn't seem to help, so I wonder if any of the other ways would maybe.
> 
> Thanks!
> 
> Florian
> 
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