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+# Environment variables in VCL
+
+## General
+
+These are the general environment variables used in the VCL:
+
+* `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_USE_SYSTEM_LOOP` - calls std::abort on nested event loop calls. Currently just for Qt with many crashes. WIP.
+
+* `SAL_NO_FONT_LOOKUP` - disable font search and fallback and always use a hard-coded font name (for some unit tests)
+* `SAL_NON_APPLICATION_FONT_USE` - control use of non-bundled fonts, values are `deny` or `abort`;
+  for now only works on platforms using fontconfig (i.e., on Linux, but neither on macOS nor on
+  Windows); also see gb_CppunitTest_set_non_application_font_use for using it in unit tests
+* `SAL_ALLOW_DEFAULT_HINTING` - use default font hinting for the platform. Enables medium/full hinting 
+  style which is otherwise reverted to (s)light.
+
+* `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
+
+* `SAL_DISABLE_WATCHDOG` - don't start the thread that watches for broken GL/Vulkan/OpenCL drivers
+
+* `SAL_NO_MOUSEGRABS` - for debugging - stop blocking UI if a breakpoint is hit
+
+## 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_DISABLEGL` - disable OpenGL use
+* `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.
+
+## 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|metal` - select Skia's drawing method, by default Vulkan or Metal are used if available
+* `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_QT_USE_QFONT` - use `QFont` for text layout and rendering (default is to use cairo)
+
+## Mac
+
+* `SAL_FORCE_HIDPI_SCALING` - set to 2 to fake HiDPI drawing (useful for unittests, windows may draw only top-left 1/4 of the content scaled)