This unifies the ImGui processing for both 2D and 3D engine.
This also make sure we don't destroy ImGui if init failed (like on older
OpenGL).
The destroy callback is also called whenever we destroy the context.
We now link with OpenGL dynamically so symbols are provided by GLAD.
If it's not supported pointer will be null.
OGLES2 should support these functions so they must be removed
This is an initial version of the emscripten build/dist target.
Many things are still missing, see dists/emscripten/README.md for
a detailed summary of what this provides and still misses
==3124361== Invalid write of size 8
==3124361== at 0x483F803: memmove (vg_replace_strmem.c:1270)
==3124361== by 0x4DBF61: SurfaceSdlGraphicsManager::grabOverlay(void*, int) const (surfacesdl-graphics.cpp:1753)
==3124361== by 0x482051: ModularGraphicsBackend::grabOverlay(void*, int) (modular-backend.cpp:215)
==3124361== by 0x434EE1: GUI::ThemeEngine::clearAll() (ThemeEngine.cpp:376)
==3124361== by 0x40128E: GUI::EventRecorder::preDrawOverlayGui() (EventRecorder.cpp:558)
==3124361== by 0x481DB2: ModularGraphicsBackend::updateScreen() (modular-backend.cpp:173)
==3124361== by 0x559967: Graphics::Screen::updateScreen() (screen.cpp:62)
==3124361== by 0x55991C: Graphics::Screen::update() (screen.cpp:56)
==3124361== by 0x38AFC7: TwinE::TwineScreen::update() (twine.cpp:126)
==3124361== by 0x3B8759: TwinE::Screens::adjustPalette(unsigned char, unsigned char, unsigned char, unsigned int const*, int) (screens.cpp:150)
==3124361== by 0x3B8A89: TwinE::Screens::fadeToPal(unsigned int const*) (screens.cpp:207)
==3124361== by 0x3B8403: TwinE::Screens::loadImage(int, int, bool) (screens.cpp:80)
==3124361== Address 0x31453050 is 16 bytes after a block of size 512,000 alloc'd
==3124361== at 0x483AB65: calloc (vg_replace_malloc.c:760)
==3124361== by 0x55B38C: Graphics::Surface::create(unsigned short, unsigned short, Graphics::PixelFormat const&) (surface.cpp:75)
==3124361== by 0x551111: Graphics::ManagedSurface::create(unsigned short, unsigned short, Graphics::PixelFormat const&) (managed_surface.cpp:153)
==3124361== by 0x4352D5: GUI::ThemeEngine::setGraphicsMode(GUI::ThemeEngine::GraphicsMode) (ThemeEngine.cpp:453)
==3124361== by 0x434A52: GUI::ThemeEngine::init() (ThemeEngine.cpp:324)
==3124361== by 0x43501B: GUI::ThemeEngine::refresh() (ThemeEngine.cpp:394)
==3124361== by 0x405780: GUI::GuiManager::screenChange() (gui-manager.cpp:603)
==3124361== by 0x405C6B: GUI::GuiManager::processEvent(Common::Event const&, GUI::Dialog*) (gui-manager.cpp:677)
==3124361== by 0x404EBA: GUI::GuiManager::runLoop() (gui-manager.cpp:429)
==3124361== by 0x3FD847: GUI::Dialog::runModal() (dialog.cpp:77)
==3124361== by 0x36D747: launcherDialog() (main.cpp:106)
==3124361== by 0x36FF92: scummvm_main (main.cpp:552)
It looks like the _videoMode.overlayHeight in SurfaceSdlGraphicsManager::grabOverlay and ThemeEngine::_backBuffer::h are somehow out of sync after
starting the game in a different resolution as the gui was started with. So the overlayHeight is updated - but the backbuffer (Surface) is not resized.
This is with event recorder being active - right after starting the game and switching the resolution.
