Get all OpenGL functions using SDL_GL_GetProcAddress(). This makes it
easier to cross-arch compile on Linux and add support for OpenGL ES
in the future.
Users still have to supply their own libSDL2 for cross-arch compiling
on Linux. But now the user does not have to re-install libgl1-mesa-dev
package for i386 or amd64 on Debian when switching between compiling
ioquake3 for x86 and x86_64.
Disable SDL relative mouse mode when in_nograb is enabled. Relative
mouse mode hides the cursor and it cannot exit the window regardless
of the window's grab state.
This wasn't always the case. SDL before 2.0.4 on GNU/Linux released
the mouse cursor in relative mode. However, SDL 2.0.3/4 on Windows
does not. (I did not test other Windows versions.) So I think SDL
2.0.4 made GNU/Linux X11 behavior consistent with other platforms.
This fixes mouse input being unusable when debuging client crashes
in gdb.
SDL doesn't provide exact the exact time that input events happen
so use the earliest possible time that an event could happen.
This make sub-frame input actions such as walking take affect
immediately instead of in the next frame.
Based on patch by Alexander "wareya" Nadeau.
Only send mouse events if both values are non-zero.
Hopefully this helps with the event overflow spam that can sometimes
happen on loads or laggy situations.
When starting the game in windowed mode, the window buffer used whatever
was on the screen before running the game. Kind of like you could see
through the window, but it doesn't update what happens behind it.
It makes it look like something is broken or non-responsive.
So clear the window opengl buffer to black.
Credit to theinvsblman for the code.
SDL1.2 branch disables key repeat when key catcher is 0.
Presumably to prevent binds from executing multiple times.
SDL2 replaced being able to disabled key repeat using SDL_EnableKeyRepeat
with a non-zero repeat value in the key event.
