1) Do not increment the frame rate returned by SDL by 1. Incrementing
is unnessecary, more or less up to date versions on Nvidias, AMDs
and Intels GPU driver on relevant platform return an value that's
either correct or rounded up to next integer. And SDL itself also
rounds up to the next integer. At least in current versions. In fact,
incrementing the value by one is harmfull, it messes our internal
timing up and leads to subtile miss predictions. Working around that
in frame.c would add another bunch of fragile magic... So just do
it correctly. If someone still has broken GPU drivers or SDL versions
that are rounding down the could set vid_displayrefreshrate.
2) The calculation of the 5% security margin to pfps in frame.c was
wrong. It didn't take into account that rfps can be slightly wrong
in the first place, e.g. 60 on an 59.95hz display. Correct it by
comparing against rfps including the margin and not the plain value.
After some pondering I realised that the changes was stupid. It
introduces some new subtile bugs, for example in some cases SDL
still rounds 59.95hz down to 59hz...
In the old world GLimp_GetRefreshRate() was called once at renderer
startup. Now in the new world with SDL 2.0 only it's called every frame
and thus the target framerate git increased by one every frame... That
lead to subtile timin problem in case that the vsync is enabled.
While here remove the hack added for some Windows GPU drivers by AMD.
Older versions returned 59 on 59.95hz displays, leading to small timing
problems. This is fixed in newer version so we don't need to work around
it. Removing the hack gives us somewhat more overall timing precision.
If someone really needs the hack vid_displayrefresh can be set to 60 to
get the old behaviour.
Make sure that the window is destroyed at gl renderer shutdown and
recreated by the soft renderer. Don't deinitialize SDL in the
softrenderer, that's done by vid.c. And make sure that we start the soft
renderer with a clean GL state.
I've chosen the minimal invasive way for this:
* Import miniz and remove -lz linker flags.
* Create a short header minizconf.h roviding everything we need
originally defined by zconf.h and not provided by miniz.
* Replace zlib.h with miniz.h and minizconf.h.
