This was done because the backdrop as implemented was the only texture in the entire game that had to be deleted and recreated each frame.
However, with Vulkan this would have necessitated quite a bit of synchronization with the render pipeline which wasn't really feasible just for this one single texture.
Now the texture manager can assume that once a texture was created it will be immutable and never has to change.
Ultimately all this needs is a small data table describing the geometric properties of each mode and a single Present function that calls the mode specific variants.
Code size got reduced from 50kb to less than 20kb with proper separation of the generic parts from the OpenGL parts.
Added ability to switch emulator and it's accuracy level ("enabling of 'run at PCM rate' reduces accuracy, and also reduces CPU usage")
Added draft code for future external banks support (WOPL format for ADLMIDI and WOPN format for OPNMIDI)
ADLMIDI 1.3.3 2018-06-19
* Fixed an inability to load another custom bank without of library re-initialization
* Optimizing the MIDI banks management system for MultiBanks (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
* Fixed incorrect 4-op counter which is still catch 4-op instruments on 2-op banks
* Fixed an incorrect processing of auto-flags
* Fixed incorrect initial MIDI tempo when MIDI file doesn't includes the tempo event
* Channel and Note Aftertouch features are now supported correctly! Aftertouch is the tremolo / vibrato, NOT A VOLUME!
* Updated DosBox OPL3 emulator up to r4111 of official DosBox trunk (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
* The automatical choosing of 4 operator channels count has been improved (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
* Added optional HQ resampler for Nuked OPL3 emulators which does usage of Zita-Resampler library (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
ADLMIDI 1.3.2 2018-04-24
* Added ability to disable MUS and XMI converters
* Added ability to disable embedded MIDI sequencer to use library as RealTime synthesizer only or use any custom MIDI sequencer plugins.
* Fixed blank instruments fallback in multi-bank support. When using non-zero bank, if instrument is blank, then, instrument will be taken from a root (I.e. zero bank).
* Added support for real-time switching the emulator
* Added support for CC-120 - "All sound off" on the MIDI channel
* Changed logic of CC-74 Brightness to affect sound only between 0 and 64 like real XG synthesizers. Ability to turn on a full-ranged brightness (to use full 0...127 range) is kept.
* Added support for different output sample formats (PCM8, PCM8U, PCM16, PCM16U, PCM32, PCM32U, Float32, and Float64) (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
* Reworked MIDI channels management to avoid any memory reallocations while music processing for a hard real time. (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
OPNMIDI 1.3.0 2018-06-19
* Optimizing the MIDI banks management system for MultiBanks (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
* Fixed incorrect initial MIDI tempo when MIDI file doesn't includes the tempo event
* Fixed an incorrect processing of auto-flags
* MAME YM2612 now results a more accurate sound as internal using of native sample rate makes more correct sound generation
* Channel and Note Aftertouch features are now supported correctly! Aftertouch is the tremolo / vibrato, NOT A VOLUME!
* Added optional HQ resampler for Nuked OPL3 emulators which does usage of Zita-Resampler library (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
OPNMIDI 1.2.0 2018-04-24
* Added ability to disable MUS and XMI converters
* Added ability to disable embedded MIDI sequencer to use library as RealTime synthesizer only or use any custom MIDI sequencer plugins.
* Fixed blank instruments fallback in multi-bank support. When using non-zero bank, if instrument is blank, then, instrument will be taken from a root (I.e. zero bank).
* Added support for real-time switching the emulator
* Added support for MAME YM2612 Emulator
* Added support for CC-120 - "All sound off" on the MIDI channel
* Changed logic of CC-74 Brightness to affect sound only between 0 and 64 like real XG synthesizers. Ability to turn on a full-ranged brightness (to use full 0...127 range) is kept.
* Added support for different output sample formats (PCM8, PCM8U, PCM16, PCM16U, PCM32, PCM32U, Float32, and Float64) (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
* Reworked MIDI channels management to avoid any memory reallocations while music processing for a hard real time. (Thanks to [Jean Pierre Cimalando](https://github.com/jpcima) for a work!)
Like Linux and macOS this will only support borderless fullscreen in the active desktop resolution now, which is what modern systems need.
The list of discrete resolutions has been removed as it makes no sense anymore with a fixed video mode - all the other scaling options remain active, though.
These files are not part of the actual renderer but part of the system code.
This means, for separated modern and legacy GL renderers, there still will only be one set of this, unlike everything else.
(concatenated "UMSH" signature + datafile + anivfile)
This is pretty much 100% functional by now.
Hasn't been tested on platforms other than Linux yet, though.
Code definitely deserves some cleaning.
* split gl_shadowmap.cpp into a GL dependent and an API independent part.
* gl_drawinfo must be kept around for the HUD sprite because it connects the renderer with the hardware indpendent part of the engine.
