Question

Qt/Embedded has the capacity to make use of hardware accelerators.
To use a hardware accelerator for a PCI or AGP driver, you need to
perform the following steps:

1. Define an accelerated descendant of QLinuxFbScreen.

   This should implement QVoodooScreen::connect() to map its
   registers. Use qt_probe_bus to get a pointer to the PCI config
   space. This is where you should check that you're being pointed to the
   right device (using the PCI device/manufacturer ID information). Then
   use PCI config space to locate your device's accelerator registers in
   physical memory and mmap the appropriate region from /dev/mem.
   There is no need to map the framebuffer, QLinuxFbScreen will do
   this for you. Return FALSE if a problem occurs at any point. QVoodooScreen::initDevice() will be called only by the QWS server and
   is guaranteed to be called before any drawing is done (and so is a
   good place to set registers to known states). connect() will be called
   by every connecting client.

2. Define an accelerated descendant of QGfxRaster.

   This is where the actual drawing code goes. Anything not implemented
   in hardware can be passed back to QGfxRaster to do in software. Use
   the optype variable to make sure that accelerated and unaccelerated
   operations are synchronised (if you start drawing via software into an
   area where the hardware accelerator is still drawing then your drawing
   operations will appear to be in the wrong order). optype is stored in
   shared memory and is set to 0 by unaccelerated operations; accelerated
   operations should set it to 1. When a software graphics operation is
   requested and optype is 1, QGfxRaster::sync() is called; you should
   provide your own implementation of this that waits for the graphics
   engine to go idle. lastop is also available for optimisation and is
   stored in the shared space - this will not be set by the software-only
   QGfx and can be used to store the type of your last operation (e.g.
   drawing a rectangle) so that part of the setup for the next operation
   can be avoided when many of the same operations are performed in
   sequence.

   All drawing operations should be protected via a QWSDisplay::grab()
   before any registers, lastop or optype are accessed, and ungrabbed() at the end. This prevents two applications trying to
   access the accelerator at once and possibly locking up the machine.
   It's possible that your source data is not on the graphics card so you
   should check in such cases and fall back to software if necessary.
   Note that QGfxRaster supports some features not directly supported
   by QPainter (for instance, alpha channels in 32-bit data and
   stretchBlt's). These features are used by Qt; stretchBlt speeds up QPixmap::xForm() and drawPixmap() into a transformed QPainter,
   alpha channel acceleration is supported for 32-bit pixmaps.

3. If you wish, define an accelerated descendant of QScreenCursor. restoreUnder(), saveUnder(), drawCursor() and draw() should
   be defined as null operations. Implement set(), move(), show() and hide(). 4k is left for your cursor at the end of the
   visible part of the framebuffer (i.e. at (width*height*depth)/8 )

4. Implement initCursor() and createGfx() in your QScreen
   descendant. Implement useOffscreen() and return TRUE if you can
   make use of offscreen graphics memory.

5. Implement a small function qt_get_screen_mychip(), which simply
   returns a new QMychipScreen

6. Add your driver to the DriverTable table in qgfxraster_qws.cpp,
   e.g.

   { "MyChip", qt_get_screen_mychip,1 },
   

   The first parameter is the name used with QWS_DISPLAY to request your
   accelerated driver.

7. To run with your new driver,

   export QWS_DISPLAY=MyChip 
   

   (optionally MyChip:/dev/fb<n> to request a different Linux
   framebuffer than /dev/fb0), then run the program

If your driver is not PCI or AGP you'll need to inherit QScreen
instead of QLinuxFbScreen and implement similar functionality to QLinuxFbScreen, but otherwise the process should be similar. The most
complete example driver is qgfxmach64_qws.cpp; qgfxvoodoo_qws.cpp may provide a smaller and easier-to-understand
driver.