Move to NanoVG for SDL's 2D graphics

[z0w0]

Use the NanoVG haskell bindings to get rid of the Cairo/Pango/Glib dependencies and move towards easier cross platform support

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[nikita-leonov]

It seems that Cairo etc for Haskell is actively supported with a last commit 6 days ago, meanwhile NanoVG last commit is 9 month ago. Do we really want to move to it, or there are more reliable options?

[z0w0]

It's a tricky situation. Cairo is well-maintained but we pull in glib and gtk which is a heavy dependency just for a game engine. Nanovg may be undermaintained but it's extremely lightweight in comparison. If there was a middleground, i.e. using Cairo without the glib/gtk dependency, I think that'd work..

[nikita-leonov]

Interesting. Do you know how gtk is used by Cairo? What I see from various documentation that GTK uses Cairo, but not vice versa. It seems that GTK manages window & surface to draw on, as well as high-level components that are drawn by Cairo, meanwhile Cairo handles low-level drawing logic. It should be easily replaceable by SDL as we already have window & surface as SDL can act as backend for Cairo in the same way as GTK. I am not sure why it depends on GTK, need to dig more.

[z0w0]

OK to clarify we don't depend on GTK directly, however:

• Cairo is part of the Haskell GTK binding project
• The Cairo bindings require installing the gtk-buildtools Haskell package or whatever it is, which makes it awkward since it's no longer as simple as just adding helm as a Cabal dependency to get up and running
• On Windows and some environments, the Cairo shared libraries are bundled with Gtk tools