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< td align = "right" valign = "center" > < img src = "logo32.png" align = "right" width = "64" height = "32" border = "0" > < / td > < / tr > < / table > < h1 align = center > Qt/Embedded Virtual Framebuffer< / h1 >
< p > The virtual framebuffer allows Qt/Embedded programs to be developed on
a desktop machine, without switching between consoles and X11.
< p > The virtual framebuffer is located in < tt > $QTDIR/tools/qvfb< / tt > .
< p > < h2 > Using the Virtual Framebuffer
< / h2 >
< a name = "1" > < / a > < p > < ol type = 1 >
< li > Configure Qt/Embedded with the < tt > -qvfb< / tt > argument and compile the library:
< pre >
./configure -qvfb
make
< / pre >
< li > Compile < tt > qvfb< / tt > as a normal Qt/X11 application and run it. Do < em > not< / em >
compile it as a Qt/Embedded application.
< li > Start a Qt/Embedded master application (i.e., construct
< a href = "qapplication.html" > QApplication< / a > with the QApplication::GuiServer flag or use the < tt > -qws< / tt > command line parameter). You can specify to the server that
you wish to use the virtual framebuffer driver, e.g.:
< pre >
masterapp -qws -display QVFb:0
< / pre >
< li > Qt/Embedded will autodetect qvfb, so you can omit the < tt > -display< / tt >
command line parameter if you know that qvfb is running, and that
the Qt/Embedded library supports qvfb. (If this is not the case,
Qt/Embedded will write to the real framebuffer, and your X11
display will be corrupted.)
< p > < / ol >
< p > < tt > qvfb< / tt > supports the following command line options:
< p > < center > < table cellpadding = "4" cellspacing = "2" border = "0" >
< tr bgcolor = "#a2c511" > < th valign = "top" > Option < th valign = "top" > Meaning
< tr bgcolor = "#f0f0f0" >
< td valign = "top" > < tt > -width< / tt > < em > width< / em >
< td valign = "top" > the width of the virtual framebuffer (default: 240).
< tr bgcolor = "#d0d0d0" >
< td valign = "top" > < tt > -height< / tt > < em > height< / em >
< td valign = "top" > the height of the virtual framebuffer (default: 320).
< tr bgcolor = "#f0f0f0" >
< td valign = "top" > < tt > -depth< / tt > < em > depth< / em >
< td valign = "top" > the depth of the virtual framebuffer (1, 8 or 32; default: 8).
< tr bgcolor = "#d0d0d0" >
< td valign = "top" > < tt > -nocursor< / tt >
< td valign = "top" > do not display the X11 cursor in the framebuffer window.
< tr bgcolor = "#f0f0f0" >
< td valign = "top" > < tt > -qwsdisplay< / tt > < em > :id< / em >
< td valign = "top" > the Qt/Embedded display id to provide (default: :0).
< / table > < / center >
< p > < h2 > Virtual Framebuffer Design
< / h2 >
< a name = "2" > < / a > < p > The virtual framebuffer emulates a framebuffer using a shared memory region
(the virtual frame buffer) and a utility to display the framebuffer in a
window (< tt > qvfb< / tt > ). The regions of the display that have changed are updated
periodically, so you will see discrete snapshots of the framebuffer rather
than each individual drawing operation. For this reason drawing problems
such as flickering may not be apparent until the program is run using a real
framebuffer.
< p > The target refresh rate can be set via the < b > View|Refresh Rate< / b >
menu item. This will cause < tt > qvfb< / tt > to check for updated regions more
frequently. The rate is a target only. If little drawing is being
done, the framebuffer will not show any updates between drawing
events. If an application is displaying an animation the updates will
be frequent, then the application and < tt > qvfb< / tt > will compete for
processor time.
< p > Mouse and keyboard events are passed to the Qt/Embedded master process via
named pipes.
< p > The virtual framebuffer is a development tool only. No security issues have
been considered in the virtual framebuffer design. It should be avoided
in a production environment; do not configure production libraries with < tt > -qvfb< / tt > .
< p >
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