On your Embedded Linux device, when there's no windowing system present, the mouse, keyboard, and touch input are read directly via
evdev
or using helper libraries such as
libinput
or
tslib
. However, this behavior requires that device nodes
/dev/input/event*
are readable by the user.
eglfs
and
linuxfb
have all the input handling code compiled-in.
libinput
is a library to handle input devices that offers an alternative to the Qt's own
evdev
input support. To enable using
libinput
, when you configure and build Qt, make sure that the development files for
libudev
and
libinput
are available. If you require keyboard support, then
xkbcommon
is also necessary. With
eglfs
and
linuxfb
, no further actions are necessary as these plugins use
libinput
by default. If
libinput
support is not available or the
QT_QPA_EGLFS_NO_LIBINPUT
environment variable is set, then Qt's own
evdev
handlers are used instead.
Parameters like the device node name can be set in the
QT_QPA_EVDEV_MOUSE_PARAMETERS
,
QT_QPA_EVDEV_KEYBOARD_PARAMETERS
and
QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS
environment variables; separate your entries with colons. These parameters are an alternative to passing the settings in the
-plugin
command-line argument, and with some backends they are essential. But
eglfs
and
linuxfb
use built-in input handlers so there's no separate
-plugin
argument in use.
Additionally, the built-in input handlers can be disabled by setting
QT_QPA_EGLFS_DISABLE_INPUT
(对于
eglfs
) 或
QT_QPA_FB_DISABLE_INPUT
(对于
linuxfb
) 到
1
.
The mouse cursor shows up whenever
QT_QPA_EGLFS_HIDECURSOR
(对于
eglfs
) 或
QT_QPA_FB_HIDECURSOR
(对于
linuxfb
) isn't set and Qt's libudev-based device discovery reports that at least one mouse is available. When
libudev
support is not present, the mouse cursor is always displayed; unless it's explicitly disabled via the environment variable.
If Qt was configured with
libudev
support, connecting or disconnecting an input device while the application is running (hot plugging) is supported. Then
libudev
development headers are present in the sysroot at configure time.
The
evdev
mouse handler supports the following extra parameters:
The
evdev
keyboard handler supports the following extra parameters:
| 参数 | 描述 |
|---|---|
/dev/input/...
|
Specifies the name of the input device. If unspecified, Qt looks for a suitable device either via
libudev
or by traversing the available nodes.
|
grab
|
Enables grabbing the input device. |
keymap
|
Specifies the name of a custom keyboard map file. |
enable-compose
|
Enables compositing. |
repeat-delay
|
Sets a custom key repeat delay. |
repeat-rate
|
Sets a custom key repeat rate. |
On Embedded Linux systems that don't have their terminal sessions disabled, the behavior on a key press can be confusing, as the input event is processed by the Qt application and the tty. To overcome this, the following options are available:
EGLFS
and
LinuxFB
attempt to disable the terminal keyboard by setting the tty's keyboard mode to
K_OFF
. This prevents keystrokes from being sent to the terminal. If the standard behavior is required, set the
QT_QPA_ENABLE_TERMINAL_KEYBOARD
环境变量到
1
. Note that this works only when the application is launched from a remote console, via
ssh
for example, and the terminal keyboard input remains enabled.
evdev
keyboard handler's
grab
parameter by passing
grab=1
in
QT_QPA_EVDEV_KEYBOARD_PARAMETERS
. This results in trying to get a grab on the input device. If the
grab
is successful, no other components in the system receive events from it, as long as the Qt application is running. This approach is more suitable for applications that start remotely as it doesn't need access to the tty device.
SYSVINIT_ENABLED_GETTYS
results in having no
getty
process running. This means, there's no input on any of the virtual terminals.
If the default built-in keymap is not sufficient, you can specify a different one either via the
keymap
parameter or via the eglfs-specific
loadKeymap()
function. The latter allows for switching the keymap at runtime. However, this behavior requires using eglfs' built-in keyboard handler; it is not supported when the keyboard handler is loaded via the
-plugin
命令行参数。
注意： Special system key combinations, such as console switching ( Ctrl+Alt+Fx ) or zap ( Ctrl+Alt+Backspace ) are not currently supported and are ignored.
To generate a custom keymap, use the
kmap2qmap
utility, that can be found in the
qttools
module. The source files have to be in standard Linux
kmap
format, which is understood by the kernel's
loadkeys
命令。
qmap
files can be generated in one of the following ways:
kmap
format with the
ckbcomp
utility.
kmap
files are plain-text files, they can also be hand crafted.
kmap2qmap
is a command line program, that needs at least 2 files as parameters. The last parameter is the generated
.qmap
file, while all the others are parsed as input
.kmap
files. For example:
kmap2qmap i386/qwertz/de-latin1-nodeadkeys.kmap include/compose.latin1.inc de-latin1-nodeadkeys.qmap
注意：
kmap2qmap
doesn't support all the (pseudo) symbols that the Linux kernel supports. Consequently, when you convert a standard keymap, there'll be a number of warnings regarding
Show_Registers
,
Hex_A
, and so on; these messages can be ignored.
While it's not necessary for modern touch screens, some resistive, single-touch touch screens may require that you fallback to using
tslib
instead of relying on the Linux multi-touch protocol and the event devices.
要启用
tslib
support, set the
QT_QPA_EGLFS_TSLIB
(对于
eglfs
) 或
QT_QPA_FB_TSLIB
(对于
linuxfb
) environment variable to 1. To change the device, set the
TSLIB_TSDEVICE
environment variable or pass the device name on the command-line. Note that the
tslib
input handler generates mouse events and supports single touch only, as opposed to
evdevtouch
which generates true multi-touch
QTouchEvent
events too.
The
evdev
touch handler supports the following extra parameters:
| 参数 | 描述 |
|---|---|
/dev/input/...
|
Specifies the name of the input device. If unspecified, Qt looks for a suitable device either via
libudev
or by traversing the available nodes.
|
rotate
|
On some touch screens the coordinates must be rotated by setting
rotate
to 90, 180, or 270.
|
invertx
and
inverty
|
Specifies the parameters to invert the X or Y coordinates in the input events. |
For example, if you pass the following values to
QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS
before launching applications, you'd have an explicitly specified touch device with the coordinates flipped. This is useful when the orientation of the actual screen and the touch screen don't match.
export QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS=/dev/input/event5:rotate=180
The
evdevtablet
plugin provides basic support for Wacom and similar pen-based tablets. It generates
QTabletEvent
events only. To enable it, pass
QT_QPA_GENERIC_PLUGINS=evdevtablet
in the environment or, alternatively, pass the
-plugin evdevtablet
argument on the command-line.
The plugin can take a device node parameter, such as
QT_QPA_GENERIC_PLUGINS=evdevtablet:/dev/event1
, if Qt's automatic device discovery (based either on
libudev
or traversing
/dev/input/event*
) isn't functional or is misbehaving.
It's possible to print some information to the debug output by enabling the
qt.qpa.input
logging rule, for example by setting the
QT_LOGGING_RULES
环境变量到
qt.qpa.input=true
. This is useful for detecting which device is being used, or for troubleshooting device discovery issues.
eglfs
comes with its own set of 32x32-sized mouse cursor images. If these are insufficient, you can provide a custom cursor atlas by setting the
QT_QPA_EGLFS_CURSOR
environment variable to the name of a JSON file. This file can also be embedded into the application via
Qt 资源系统
.
For example, an embedded cursor atlas with 8 cursor images per row can be specified as follows:
{
"image": ":/cursor-atlas.png",
"cursorsPerRow": 8,
"hotSpots": [
[7, 2],
[12, 3],
[12, 12],
...
]
}
Note that the images are expected to be tightly packed in the atlas; the width and height of the cursors are determined based on the total image size and the
cursorsPerRow
setting. Atlases must also provide an image for all of the supported cursors.