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This commit squashes multiple commits by illwieckz and slipher.

See #478

Co-authored-by: Thomas “illwieckz” Debesse <[email protected]>
Co-authored-by: slipher <[email protected]>

== Squashed commits by illwieckz

:: sdl_glimp: rewrite the original GL selection code

- Detect best configuration possible.
- Try custom configuration if exists.
- If no custom configuration or if it fails,
  load the recommended configuration if
  possible (OpenGL 3.2 core) or the best
  one available.
- Reuse window and context when possible.
- Display meaningful popup telling user
  OpenGL version is too low or required
  extensions are missing when that happens.
- Rely on more return codes for GLimp_SetMode().
- Test for negative SDL_Init return value,
  not just -1.

:: sdl_glimp,tr_init: do not test all OpenGL versions unless r_glExtendedValidation is set

When r_glExtendedValidation is enabled, the engine
tests if OpenGL versions higher than 3.2 core
are supported for logging and diagnostic purpose,
but still requestes 3.2 core anyway. Some drivers
may provide more than 3.2 when requesting 3.2, this
is not our fault.

:: sdl_glimp,tr_init: rewrite logging, improve gfxinfo

- Move GL query for logging purpose from tr_init to sdl_glimp.
- Do not split MODE log message.
- Unify some log.
- Add more debug log when building GL extension list.
- Also increase the extensions_string length to not
  truncate the string, 4096 is not enough, there can
  be more than 6000 characters on an OpenGL 4.6 driver.
- Also log missing extensions to make gfxinfo more useful.
- Rewrite gfxinfo in more useful way.
- List enabled and missing GL extensions.

:: sdl_glimp: silence the GL error when querying if context
is core on non-core implementation

- Silence the error that may happen when querying if the
  OpenGL context uses core profile when core profile is not
  supported by the OpenGL implementation to begin with.

For example this may happen on implementations not supporting
higher than OpenGL 2.1, while forcing OpenGL 2.1 on
implementations supporting higher versions including
core profiles may not raise an error.

:: sdl_glimp: make GLimp_StartDriverAndSetMode only return true on RSERR_OK

- Only return true on OK, don't return true on unknown errors.

:: sdl_glimp: catch errors from GLimp_DetectAvailableModes to prevent further segfault

It may be possible to create a valid context that is unusable.

For example the 3840×2160 resolution is too large for the
Radeon 9700 and the Mesa r300 driver may print this error
when the requested resolution is higher than what is supported
by hardware:

> r300: Implementation error: Render targets are too big in r300_set_framebuffer_state, refusing to bind framebuffer state!

It will unfortunately return a valid but unusable context that will
make the engine segfault when calling GL_SetDefaultState().

:: sdl_glimp: flag fullscreen window as borderless when borderless is enabled

Flag fullscreen window as borderless when borderless is enabled
otherwise the window will be bordered when leaving fullscreen
while the borderless option would be enabled.

:: sdl_glimp,tr_init: remove unused depthBits

:: sdl_glimp: remove SDL_INIT_NOPARACHUTE

In GLimp_StartDriverAndSetMod() the SDL_INIT_NOPARACHUTE flag was
removed from SDL_Init( SDL_INIT_VIDEO ) as this flag is now
ignored, see https://wiki.libsdl.org/SDL_Init

== Squashed commits by slipher

:: Better type safety in GL detection code

:: Simplify GL_ValidateBestContext duplicate loop

:: GLimp_SetMode - simplify error handling

:: Rework GL initialization

Have GLimp_ValidateBestContext() validate both the highest-numbered
available context (if r_glExtendedValidation is enabled), and the
highest context that we actually want to use (at most 3.2). This means
most of the code in GLimp_ApplyPreferredOptions can be removed because
it was duplicating the knowledge about version preferences and the code
for instantiating them in GLimp_ValidateBestContext.

:: Also cut down on other code duplication.

:: Remove dead cvar r_stencilBits

:: Fix glConfig.colorBits logging

- show actual not requested
- don't log it twice at notice level

This may not be enough to make the game run on such
hardware anyway.

The Mesa i915 driver for GMA Gen 3 disabled GL 2.1 on such
hardware to force Google Chrome to use its CPU fallback
that was faster but we don't implement such fallback.
See https://gitlab.freedesktop.org/mesa/mesa/-/commit/a1891da7c865c80d95c450abfc0d2bc49db5f678

Only Mesa i915 on Linux supports GL 2.1 for GMA Gen 3,
so there is no similar tweak being required for Windows
and macOS.

Enabling those options would at least make the engine
properly report missing extension instead of missing
GL version, for example the Intel GMA 3100 G33 (Gen 3)
will report missing GL_ARB_half_float_vertex extension
instead of missing OpenGL 2.1 version.

The GMA 3150 is known to have wider OpenGL support than
GMA 3100, for example it has OpenGL version similar to
GMA 4 on Windows while being a GMA 3 so the list of
available GL extensions may be larger.

Thanks papap and its LanPower association for the kind
report and availability for testing.
http://asso.lanpower.free.fr