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45 \title The Virtual Framebuffer
46 \ingroup qt-embedded-linux
48 \l{Qt for Embedded Linux} applications write directly to the
49 framebuffer, eliminating the need for the X Window System and
50 saving memory. For development and debugging purposes, a virtual
51 framebuffer can be used, allowing \l{Qt for Embedded Linux}
52 programs to be developed on a desktop machine, without switching
53 between consoles and X11.
55 QVFb is an X11 application supplied with Qt for X11 that provides
56 a virtual framebuffer for Qt for Embedded Linux to use. To use it,
57 you need to \l{Installing Qt on X11 Platforms}{configure and
58 install Qt on X11 platforms} appropriately. Further requirements
59 can be found in the \l{Qt for Embedded Linux Requirements}
62 \image qt-embedded-virtualframebuffer.png
64 The virtual framebuffer emulates a framebuffer using a shared
65 memory region and the \c qvfb tool to display the framebuffer in a
66 window. The \c qvfb tool also supports a feature known as a skin
67 which can be used to change the look and feel of the display. The
68 tool is located in Qt's \c tools/qvfb directory, and provides
69 several additional features accessible through its \gui File and
72 Please note that the virtual framebuffer is a development tool
73 only. No security issues have been considered in the virtual
74 framebuffer design. It should be avoided in a production
75 environment; i.e. do not configure production libraries with the
80 \section1 Displaying the Virtual Framebuffer
82 To run the \c qvfb tool displaying the virtual framebuffer, the
83 \l{Qt for Embedded Linux} library must be configured and compiled
84 with the \c -qvfb option:
86 \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 0
88 Ensure that you have all the
89 \l{Qt for Embedded Linux Requirements#Additional X11 Libraries for QVFb}
90 {necessary libraries} needed to build the tool, then compile and run the
91 \c qvfb tool as a normal Qt for X11 application (i.e., do \e not compile
92 it as a \l{Qt for Embedded Linux} application):
94 \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 1
96 The \c qvfb application supports the following command line
100 \header \o Option \o Description
102 \o \c {-width <value>}
103 \o The width of the virtual framebuffer (default: 240).
105 \o \c {-height <value>}
106 \o The height of the virtual framebuffer (default: 320).
108 \o \c {-depth <value>}
109 \o The depth of the virtual framebuffer (1, 8 or 32; default: 8).
112 \o Do not display the X11 cursor in the framebuffer window.
114 \o \c {-qwsdisplay <:id>}
115 \o The \l{Qt for Embedded Linux} display ID (default: 0).
117 \o \c {-skin <name>.skin}
118 \o The preferred skin. Note that the skin must be located in Qt's
119 \c /tools/qvfb/ directory.
121 \o \c {-zoom <factor>}
122 \o Scales the application view with the given factor.
128 A skin is a set of XML and pixmap files that tells the vitual
129 framebuffer what it should look like and how it should behave; a
130 skin can change the unrealistic default display into a display
131 that is similar to the target device. To access the \c qvfb tool's
132 menus when a skin is activated, right-click over the display.
134 Note that a skin can have buttons which (when clicked) send
135 signals to the Qt Extended application running inside the virtual
136 framebuffer, just as would happen on a real device.
141 \bold {Target Device Environment}
143 The \c qvfb tool provides various skins by default, allowing
144 the user to view their application in an environment similar
145 to their target device. The provided skins are:
152 \o Qt ExtendedPhone-Advanced
153 \o Qt ExtendedPhone-Simple
156 \o SmartPhoneWithButtons
159 \o Trolltech-Touchscreen
162 In addition, it is possible to create custom skins.
164 \o \image qt-embedded-phone.png
165 \o \image qt-embedded-pda.png
168 \bold {Creating Custom Skins}
170 The XML and pixmap files specifying a custom skin must be located
171 in subdirectory of the Qt's \c /tools/qvfb directory, called \c
172 /customskin.skin. See the ClamshellPhone skin for an example of the
175 \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 2
177 The \c /ClamshellPhone.skin directory contains the following files:
180 \o \c ClamshellPhone.skin
181 \o \c ClamshellPhone1-5.png
182 \o \c ClamshellPhone1-5-pressed.png
183 \o \c ClamshellPhone1-5-closed.png
184 \o \c defaultbuttons.conf (only necessary for \l Qt Extended)
187 Note that the \c defaultbuttons.conf file is only necessary if the
188 skin is supposed to be used with \l Qt Extended (The file customizes
189 the launch screen applications, orders the soft keys and provides
190 input method hints). See the \l Qt Extended documentation for more
195 \o {3,1} The ClamshellPhone Skin
199 \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 3
201 The \c ClamShellPhone.skin file quoted above, specifies three
202 pixmaps: One for the normal skin (\c Up), one for the activated
203 skin (\c Down) and one for the closed skin (\c Closed). In
204 addition, it is possible to specify a pixmap for the cursor (using
205 a \c Cursor variable).
207 The file also specifies the screen size (\c Screen) and the number
208 of available buttons (\c Areas). Then it describes the buttons
209 themselves; each button is specified by its name, keycode and
212 The coordinates are a list of at least 2 points in clockwise order
213 that define a shape for the button; a click inside this shape will
214 be treated as a click on that button. While pressed, the pixels
215 for the button are redrawn from the activated skin.
220 \image qt-embedded-clamshellphone-closed.png The ClamshellPhone Skin (closed)
222 \image qt-embedded-clamshellphone.png The ClamshellPhone Skin
224 \image qt-embedded-clamshellphone-pressed.png The ClamshellPhone Skin (pressed)
226 \o \c ClamshellPhone1-5-closed.png
227 \o \c ClamshellPhone1-5.png
228 \o \c ClamshellPhone1-5-pressed.png
231 \section2 The File Menu
233 \image qt-embedded-qvfbfilemenu.png
235 The \gui File menu allows the user to configure the virtual
236 framebuffer display (\gui File|Configure...), save a snapshot of
237 the framebuffer contents (\gui {File|Save Image...}) and record
238 the movements in the framebuffer (\gui File|Animation...).
240 When choosing the \gui File|Configure menu item, the \c qvfb tool
241 provides a configuration dialog allowing the user to customize the
242 display of the virtual framebuffer. The user can modify the size
243 and depth as well as the Gamma values, and also select the
244 preferred skin (i.e. making the virtual framebuffer simulate the
245 target device environment). In addition, it is possible to emulate
246 a touch screen and a LCD screen.
248 Note that when configuring (except when changing the Gamma values
249 only), any applications using the virtual framebuffer will be
252 \section2 The View Menu
254 \image qt-embedded-qvfbviewmenu.png
256 The \gui View menu allows the user to modify the target's refresh
257 rate (\gui {View|Refresh Rate...}), making \c qvfb check for
258 updated regions more or less frequently.
260 The regions of the display that have changed are updated
261 periodically, i.e. the virtual framebuffer is displaying discrete
262 snapshots of the framebuffer rather than each individual drawing
263 operation. For this reason drawing problems such as flickering may
264 not be apparent until the program is run using a real framebuffer.
265 If little drawing is being done, the framebuffer will not show any
266 updates between drawing events. If an application is displaying an
267 animation, the updates will be frequent, and the application and
268 \c qvfb will compete for processor time.
270 The \gui View menu also allows the user to zoom the view of the
271 application (\gui {View|Zoom *}).
273 \section1 Running Applications Using the Virtual Framebuffer
275 Once the virtual framebuffer (the \c qvfb application) is running,
276 it is ready for use: Start a server application (i.e. construct a
277 QApplication object with the QApplication::GuiServer flag or use
278 the \c -qws command line parameter. See the
279 \l {Running Qt for Embedded Linux Applications}{running applications}
280 documentation for details). For example:
282 \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 4
284 Note that as long as the virtual framebuffer is running and the
285 current \l{Qt for Embedded Linux} configuration supports \c qvfb,
286 \l{Qt for Embedded Linux} will automatically detect it and use it by
287 default. Alternatively, the \c -display option can be used to
288 specify the virtual framebuffer driver. For example:
290 \snippet doc/src/snippets/code/doc_src_emb-qvfb.qdoc 5
292 \warning If \c qvfb is not running (or the current
293 \l{Qt for Embedded Linux} configuration doesn't support it) and the
294 driver is not explicitly specified, \l{Qt for Embedded Linux} will
295 write to the real framebuffer and the X11 display will be corrupted.