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| 32 | <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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| 33 |
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| 34 |
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| 35 |
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| 36 | <p> Qt/Embedded has the capacity to make use of hardware accelerators.
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| 37 | To use a hardware accelerator for a PCI or AGP driver, you must
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| 38 | perform the following steps:
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| 39 | <p> <ol type=1>
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| 40 | <li>
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| 41 | Define an accelerated descendant of QLinuxFbScreen.
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| 42 | <p> This should implement <tt>QVoodooScreen::connect()</tt> to map its
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| 43 | registers. Use <tt>qt_probe_bus</tt> to get a pointer to the PCI config
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| 44 | space. This is where you should check that you're being pointed to the
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| 45 | right device (using the PCI device/manufacturer ID information). Then
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| 46 | use PCI config space to locate your device's accelerator registers in
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| 47 | physical memory and mmap the appropriate region from <tt>/dev/mem</tt>.
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| 48 | There is no need to map the framebuffer, <tt>QLinuxFbScreen</tt> will do
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| 49 | 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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| 50 | is guaranteed to be called before any drawing is done (and so is a
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| 51 | good place to set registers to known states). <tt>connect()</tt> will be called
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| 52 | by every connecting client.
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| 53 | <p> <li>
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| 54 | Define an accelerated descendant of QGfxRaster.
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| 55 | <p> This is where the actual drawing code goes. Anything not implemented
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| 56 | in hardware can be passed back to <tt>QGfxRaster</tt> to do in software. Use
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| 57 | the optype variable to make sure that accelerated and unaccelerated
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| 58 | operations are synchronised (if you start drawing via software into an
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| 59 | area where the hardware accelerator is still drawing then your drawing
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| 60 | operations will appear to be in the wrong order). optype is stored in
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| 61 | shared memory and is set to 0 by unaccelerated operations; accelerated
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| 62 | operations should set it to 1. When a software graphics operation is
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| 63 | requested and optype is 1, <tt>QGfxRaster::sync()</tt> is called; you should
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| 64 | provide your own implementation of this that waits for the graphics
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| 65 | engine to go idle. lastop is also available for optimisation and is
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| 66 | stored in the shared space: this will not be set by the software-only
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| 67 | <tt>QGfx</tt> and can be used to store the type of your last operation (e.g.
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| 68 | drawing a rectangle) so that part of the setup for the next operation
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| 69 | can be avoided when many of the same operations are performed in
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| 70 | sequence.
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| 71 | <p> All drawing operations should be protected via a <tt>QWSDisplay::grab()</tt>
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| 72 | 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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| 73 | access the accelerator at once and possibly locking up the machine.
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| 74 | It's possible that your source data is not on the graphics card so you
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| 75 | should check in such cases and fall back to software if necessary.
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| 76 | Note that <tt>QGfxRaster</tt> supports some features not directly supported
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| 77 | by <a href="qpainter.html">QPainter</a> (for instance, alpha channels in 32-bit data and
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| 78 | 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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| 79 | alpha channel acceleration is supported for 32-bit pixmaps.
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| 80 | <p> <li>
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| 81 | 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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| 82 | 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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| 83 | visible part of the framebuffer (i.e. at (width*height*depth)/8 )
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| 84 | <p> <li>
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| 85 | Implement <tt>initCursor()</tt> and <tt>createGfx()</tt> in your <a href="qscreen.html">QScreen</a>
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| 86 | descendant. Implement <tt>useOffscreen()</tt> and return <tt>TRUE</tt> if you can
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| 87 | make use of offscreen graphics memory.
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| 88 | <p> <li>
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| 89 | Implement a small function <tt>qt_get_screen_mychip()</tt>, which simply
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| 90 | returns a new <tt>QMychipScreen</tt>
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| 91 | <p> <li>
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| 92 | Add your driver to the DriverTable table in <tt>qgfxraster_qws.cpp</tt>,
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| 93 | e.g.
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| 94 | <pre>
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| 95 | { "MyChip", qt_get_screen_mychip,1 },
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| 96 | </pre>
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| 97 |
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| 98 | <p> The first parameter is the name used with QWS_DISPLAY to request your
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| 99 | accelerated driver.
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| 100 | <p> <li>
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| 101 | To run with your new driver,
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| 102 | <pre>
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| 103 | export QWS_DISPLAY=MyChip
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| 104 | </pre>
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| 105 |
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| 106 | (optionally MyChip:/dev/fb<n> to request a different Linux
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| 107 | framebuffer than <tt>/dev/fb0</tt>), then run the program
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| 108 | <p> </ol>
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| 109 | <p> If your driver is not PCI or AGP you'll need to inherit <a href="qscreen.html">QScreen</a>
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| 110 | 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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| 111 | 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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| 112 | driver.
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| 113 | <p>
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| 114 | <!-- eof -->
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| 115 | <p><address><hr><div align=center>
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| 117 | <td>Copyright © 2007
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| 118 | <a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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| 119 | <td align=right><div align=right>Qt 3.3.8</div>
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| 120 | </table></div></address></body>
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