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122 lines
6.1 KiB
122 lines
6.1 KiB
14 years ago
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/accel.doc:36 -->
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<title>Adding an accelerated graphics driver to Qt/Embedded</title>
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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>Adding an accelerated graphics driver to Qt/Embedded</h1>
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<p> Qt/Embedded has the capacity to make use of hardware accelerators.
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To use a hardware accelerator for a PCI or AGP driver, you must
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perform the following steps:
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<p> <ol type=1>
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<li>
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Define an accelerated descendant of QLinuxFbScreen.
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<p> This should implement <tt>QVoodooScreen::connect()</tt> to map its
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registers. Use <tt>qt_probe_bus</tt> to get a pointer to the PCI config
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space. This is where you should check that you're being pointed to the
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right device (using the PCI device/manufacturer ID information). Then
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use PCI config space to locate your device's accelerator registers in
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physical memory and mmap the appropriate region from <tt>/dev/mem</tt>.
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There is no need to map the framebuffer, <tt>QLinuxFbScreen</tt> will do
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this for you. Return <tt>FALSE</tt> if a problem occurs at any point. <tt>QVoodooScreen::initDevice()</tt> will be called only by the QWS server and
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is guaranteed to be called before any drawing is done (and so is a
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good place to set registers to known states). <tt>connect()</tt> will be called
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by every connecting client.
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<p> <li>
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Define an accelerated descendant of QGfxRaster.
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<p> This is where the actual drawing code goes. Anything not implemented
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in hardware can be passed back to <tt>QGfxRaster</tt> to do in software. Use
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the optype variable to make sure that accelerated and unaccelerated
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operations are synchronised (if you start drawing via software into an
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area where the hardware accelerator is still drawing then your drawing
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operations will appear to be in the wrong order). optype is stored in
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shared memory and is set to 0 by unaccelerated operations; accelerated
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operations should set it to 1. When a software graphics operation is
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requested and optype is 1, <tt>QGfxRaster::sync()</tt> is called; you should
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provide your own implementation of this that waits for the graphics
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engine to go idle. lastop is also available for optimisation and is
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stored in the shared space: this will not be set by the software-only
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<tt>QGfx</tt> and can be used to store the type of your last operation (e.g.
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drawing a rectangle) so that part of the setup for the next operation
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can be avoided when many of the same operations are performed in
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sequence.
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<p> All drawing operations should be protected via a <tt>QWSDisplay::grab()</tt>
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before any registers, lastop or optype are accessed, and <tt>ungrabbed()</tt> at the end. This prevents two applications trying to
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access the accelerator at once and possibly locking up the machine.
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It's possible that your source data is not on the graphics card so you
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should check in such cases and fall back to software if necessary.
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Note that <tt>QGfxRaster</tt> supports some features not directly supported
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by <a href="qpainter.html">QPainter</a> (for instance, alpha channels in 32-bit data and
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stretchBlt's). These features are used by Qt; stretchBlt speeds up <a href="qpixmap.html#xForm">QPixmap::xForm</a>() and <tt>drawPixmap()</tt> into a transformed <a href="qpainter.html">QPainter</a>,
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alpha channel acceleration is supported for 32-bit pixmaps.
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<p> <li>
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If you wish, define an accelerated descendant of <tt>QScreenCursor</tt>. <tt>restoreUnder()</tt>, <tt>saveUnder()</tt>, <tt>drawCursor()</tt> and <tt>draw()</tt> should
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be defined as null operations. Implement <tt>set()</tt>, <tt>move()</tt>, <tt>show()</tt> and <tt>hide()</tt>. 4KB is left for your cursor at the end of the
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visible part of the framebuffer (i.e. at (width*height*depth)/8 )
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<p> <li>
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Implement <tt>initCursor()</tt> and <tt>createGfx()</tt> in your <a href="qscreen.html">QScreen</a>
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descendant. Implement <tt>useOffscreen()</tt> and return <tt>TRUE</tt> if you can
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make use of offscreen graphics memory.
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<p> <li>
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Implement a small function <tt>qt_get_screen_mychip()</tt>, which simply
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returns a new <tt>QMychipScreen</tt>
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<p> <li>
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Add your driver to the DriverTable table in <tt>qgfxraster_qws.cpp</tt>,
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e.g.
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<pre>
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{ "MyChip", qt_get_screen_mychip,1 },
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</pre>
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<p> The first parameter is the name used with QWS_DISPLAY to request your
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accelerated driver.
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<p> <li>
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To run with your new driver,
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<pre>
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export QWS_DISPLAY=MyChip
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</pre>
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(optionally MyChip:/dev/fb<n> to request a different Linux
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framebuffer than <tt>/dev/fb0</tt>), then run the program
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<p> </ol>
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<p> If your driver is not PCI or AGP you'll need to inherit <a href="qscreen.html">QScreen</a>
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instead of <tt>QLinuxFbScreen</tt> and implement similar functionality to <tt>QLinuxFbScreen</tt>, but otherwise the process should be similar. The most
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complete example driver is <tt>qgfxmach64_qws.cpp</tt>; <tt>qgfxvoodoo_qws.cpp</tt> may provide a smaller and easier-to-understand
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driver.
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<p>
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<!-- eof -->
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<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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