Environment variables in VCL:

General
-------
SAL_USE_VCLPLUGIN - use a VCL plugin
SAL_RTL_ENABLED - Enable RTL UI
SAL_NO_NWF - disable native widgets
SAL_FORCEDPI - force a specific DPI (gtk3 & qt5/kf5 plugins only)
SAL_FORCE_HC - force high-contrast mode

SAL_NO_FONT_LOOKUP - disable font search and fallback and always use a hard-coded font name (for some unit tests)

LO_COLLECT_UIINFO - enable the uitesting logging, value is expected to be a relative file name that
will be used to write the log under instdir/uitest/.

VCL_DOUBLEBUFFERING_AVOID_PAINT - don't paint the buffer, useful to see where we do direct painting
VCL_DOUBLEBUFFERING_FORCE_ENABLE - enable double buffered painting
VCL_DOUBLEBUFFERING_ENABLE - enable a safe subset of double buffered painting (currently in Writer, not in any other applications)

VCL_DEBUG_DISABLE_PDFCOMPRESSION - disable compression in the PDF writer

Gtk+
----
VCL_GTK3_PAINTDEBUG - in debug builds, if set to 1 then holding down shift+0 forces a redraw event, shift+1 repaints everything, and
shift+2 dumps cairo frames to pngs as /tmp/frame<n>.png
GDK_SCALE=2 - for HiDPI scaling (just supports integers)

Bitmap
------
VCL_NO_THREAD_SCALE - disable threaded bitmap scale
VCL_NO_THREAD_IMPORT - disable threaded bitmap import
EMF_PLUS_DISABLE - use EMF rendering and ignore EMF+ specifics

OpenGL
------
SAL_FORCEGL - force enable OpenGL
SAL_GL_NO_SWAP - disable buffer swapping if set (should show nothing)
SAL_GL_SLEEP_ON_SWAP - sleep for half a second on each swap-buffers.
SAL_DISABLE_WATCHDOG - don't start the thread that watches for broken GL/Vulkan/OpenCL drivers
SAL_DISABLE_GLYPH_CACHING - don't render glyphs through OpenGL textures or Skia surfaces

Skia
----
SAL_DISABLESKIA=1 - force disabled Skia
SAL_ENABLESKIA=1 - enable Skia, unless denylisted (and if the VCL backend supports Skia)
SAL_FORCESKIA=1 - force using Skia, even if denylisted
SAL_SKIA=raster|vulkan - select Skia's drawing method, by default Vulkan is used
SAL_DISABLE_SKIA_CACHE=1 - disable caching of complex images
SAL_SKIA_KEEP_BITMAP_BUFFER=1 - SkiaSalBitmap will keep its bitmap buffer even after storing in SkImage

OpenGL,Skia
-----------
SAL_WITHOUT_WIDGET_CACHE - disable LRU caching of native widget textures

Qt
-----
QT_SCALE_FACTOR=2 - for HiDPI testing (also supports float)
SAL_VCL_QT5_NO_FONTCONFIG - ignore fontconfig provided font substitutions
SAL_VCL_QT5_NO_NATIVE - disable QStyle'd controls
SAL_VCL_QT5_USE_CAIRO - use cairo for text rendering and fonts (default for kf5, but not qt5)
