Fixed bug 3786 - building against a Mac OS X SDK < 10.11 fails since the vulkan merge

Ozkan Sezer

Since the Vulkan merge, building against a Mac OS X SDM older than
10.11 fails in SDL_cocoametalview.m because Metal.framework is not
present. There is no conditional compiling in SDL_cocoametalview.m
either, so --disable-video-vulkan doesn't help with anything. (The
configury doesn't check darwin for x86_64 either, but it's another
story.)

I cross-build against 10.8 SDK on linux using clang-3.4.2 and this
is a problem for me. Will this be fixed?

Fixed bug 3662 - Error message when using the audio conversion setup without an initialized audio subsystem is a bit vague

Simon Hug

This issue actually raises the question if this API change (requirement of initialized audio subsystem) is breaking backwards compatibility. I don't see the documentation saying it is needed in 2.0.5.

audio: A whole bunch of improvements to audio conversion (thanks, Solra!).

"Major changes, roughly in order of appearance:

- Use float math everywhere, instead of promoting to double and casting back
all the time.
- Conserve sound energy when downmixing any channel into two other channels.
- Add a QuadToStereo filter. (The previous technique of reusing StereoToMono
never worked, since it assumed an incorrect channel layout for 4.0.)
- Add a 71to51 filter. This removes just under half of the cases the previous
code would silently break in.
- Add a QuadTo51 filter. More silent breakage fixed.
- Add a 51to71 filter, removing another almost-half of the silently broken
cases.
- Add 8 to the list of values SDL_SupportedChannelCount will accept.
- Change SDL_BuildAudioCVT's channel-related logic to handle every case, and
to actually fail if it fails instead of silently corrupting sound data and/or
crashing down the road."

(Note that SDL doesn't otherwise support 7.1 audio yet, but hopefully it will
soon and the 7.1 converters are an important piece of that. --ryan.)

Fixes Bugzilla #3727.

stdlib: An implementation of SDL_scalbn using ldexp() (thanks, Ozkan!).

Fixes Bugzilla #3767.

audio: Converting audio samples from int to float was using wrong equation.

Fixes Bugzilla #3775.

Fixed building with an older Mac OS X SDK

Vulkan support on Mac OS X introduces a link time dependency (CAMetalLayer) on 10.11 and newer

We don't need the VULKAN_SDK to build SDL with Vulkan support anymore

Added missing Visual Studio 2010 project for testvulkan

Fixed compile warning