embedded: Improve env var and input param docs

Task-number: QTBUG-56021
Change-Id: I565712cd7b5f81ccb9cffacba874f49bf596c198
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>

doc/src/platforms/emb-linux.qdoc

@@ -187,6 +187,23 @@
   application type. The special cursor implementations, such as the KMS/DRM
   backend's hardware cursor, may not support rotation.
 
+  \li \c {QT_QPA_EGLFS_FORCEVSYNC} - When set, \c eglfs requests
+  \c FBIO_WAITFORVSYNC on the framebuffer device after each call to
+  eglSwapBuffers(). This is only relevant for backends relying on the legacy
+  \c fbdev subsystem of Linux. Normally, with a default swap interval of 1, Qt
+  assumes that calling eglSwapBuffers() takes care of vsync; if it doesn't (for
+  example, due to driver bugs), try setting \c QT_QPA_EGLFS_FORCEVSYNC to a
+  non-zero value.
+
+  \li \c {QT_QPA_EGLFS_FORCE888} - When set, the red, green, and blue color
+  channel sizes are ignored whenever creating a new context, window or offscreen
+  surface. Instead, the plugin requests a configuration with 8 bits per
+  channel. This can be helpful on devices where configurations with less than 32
+  or 24 bits per pixel (for example, 5-6-5 or 4-4-4) are chosen by default but
+  are known not to be ideal, for example, due to banding effects. Instead of
+  changing application code, this variable provides an easier shortcut to force
+  24 or 32 bpp configurations.
+
   \endlist
 
   In addition, the following - less commonly used - variables are
@@ -219,18 +236,6 @@
   0 will disable blocking on swap, resulting in running as fast as possible
   without any synchronization.
 
-  \li \c {QT_QPA_EGLFS_FORCEVSYNC} - When set, \c eglfs requests
-  \c FBIO_WAITFORVSYNC on the framebuffer device.
-
-  \li \c {QT_QPA_EGLFS_FORCE888} - When set, the red, green, and blue color
-  channel sizes are ignored whenever creating a new context, window or offscreen
-  surface. Instead, the plugin requests a configuration with 8 bits per
-  channel. This can be helpful on devices where configurations with less than 32
-  or 24 bits per pixel are chosen by default but are known to be not suitable,
-  for example, due to banding effects. Instead of changing all the applications,
-  this variable provides an easier shortcut to force 24/32 bpp configurations
-  for a given device.
-
   \li \c {QT_QPA_EGLFS_DEBUG} - When set, some debugging information is printed
   on the debug output. For example, the input QSurfaceFormat and the properties
   of the chosen EGL configuration are printed while creating a new
@@ -354,11 +359,14 @@
 
   Parameters like the device node name can be set in the environment variables
   \c QT_QPA_EVDEV_MOUSE_PARAMETERS, \c QT_QPA_EVDEV_KEYBOARD_PARAMETERS and
-  \c QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS. Additionally, the built-in input handlers
-  can be disabled by setting \c QT_QPA_EGLFS_DISABLE_INPUT or
-  \c QT_QPA_FB_DISABLE_INPUT to \c 1. On some touch screens the coordinates must
-  be rotated, which is done by setting
-  \c QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS to \c {rotate=180}.
+  \c QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS. Separate the entries with colons.  These
+  parameters act as an alternative to passing the settings in the \c{-plugin}
+  command-line argument, and with some backends they are essential: eglfs and
+  linuxfb use built-in input handlers so there is no separate \c {-plugin}
+  argument in use.
+
+  Additionally, the built-in input handlers can be disabled by setting
+  \c QT_QPA_EGLFS_DISABLE_INPUT or \c QT_QPA_FB_DISABLE_INPUT to \c 1.
 
   \section2 Mouse
 
@@ -373,6 +381,29 @@
   configure time). This allows connecting or disconnecting an input device while
   the application is running.
 
+  The \e evdev mouse handler supports the following extra parameters:
+
+  \list
+
+  \li \c {/dev/input/...} - Specifies the name of the input device. When not
+  given, Qt looks for a suitable device either via \e libudev or by walking
+  through the available nodes.
+
+  \li \c nocompress - By default, input events that do not lead to changing the
+  position compared to the last Qt mouse event are compressed; a new Qt mouse
+  event is sent only after a change in the position or button state.  This can
+  be disabled by setting the \c nocompress parameter.
+
+  \li \c dejitter - Specifies a jitter limit. By default dejittering is disabled.
+
+  \li \c grab - When 1, Qt will grab the device for exclusive use.
+
+  \li \c abs - Some touchscreens report absolute coordinates and cannot be
+  differentiated from touchpads.  In this special situation pass \c abs to
+  indicate that the device is using absolute events.
+
+  \endlist
+
   \section2 Keyboard
 
   The \e evdev keyboard handler supports the following extra parameters:
@@ -468,6 +499,28 @@
   supports single touch only, as opposed to \c evdevtouch which generates true
   multi-touch QTouchEvent events too.
 
+  The \e evdev touch handler supports the following extra parameters:
+
+  \list
+
+  \li \c {/dev/input/...} - Specifies the name of the input device. When not
+  given, Qt looks for a suitable device either via \e libudev or by walking
+  through the available nodes.
+
+  \li \c rotate - On some touch screens the coordinates must be rotated, which
+  is done by setting \c rotate to 90, 180, or 270.
+
+  \li \c invertx and \c inverty - To invert the X or Y coordinates in the input
+  events, pass \c invertx or \c inverty.
+
+  \endlist
+
+  For example, doing \c{export
+  QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS=/dev/input/event5:rotate=180} before
+  launching applications results in an explicitly specified touch device and
+  flipping the coordinates - useful when the orientation of the actual
+  screen and the touch screen do not match.
+
   \section2 Pen-based tablets
 
   The \c evdevtablet plugin provides basic support for Wacom and similar,