On Mon, Feb 6, 2017 at 1:52 PM, William Hermans <yyrk...@gmail.com> wrote: >> >> Something I noticed is that if I pipe /dev/urandom to /dev/fb0, I get all the random colors, even in the left blank area when the image is shifted. Then I started our app and the top left 10 or so pixels remained the random colors. If I then using dd fill /dev/fb0 with zero from /dev/null, everything becomes black, including the top left row. I am not sure what all this means yet... > > > /dev/fb0 is most likely a direct access frame buffer for the video device. In the case, the SGX video chip. I honestly do not know about the Linux frame buffer in great detail. But if it works similar to how old VGA frame buffers work. Essentially it's a two dimensional array. Similar to how you plot a coordinate in geometry. So think 1024( up / down ) rows, of 768( left to right ) columns. > > Absolute top left is considered coordinate 0,0, where absolute opposite would be 1023, 767. How a frame buffer works, is that once you go over the maximum value in width(767), you wrap back to 0(most left ), and drop down a row. If that row is your maximum height, then there are a couple this can be implemented. Wrap back to 0 height, or continue on to the next "page" Which is how sometimes frame buffering is done. Again, I do not know the Linux frame buffer specification at all, so this part I'm not sure how this is dealt with. > > Anyway, this makes it really simple, and fast to "blast" or blit changed to screen. As the whole screen is seen at one large file, with x amount of bytes. Each byte representing a pixel on screen. While each byte value represents the actual color of that pixel. So when you dd random values into this file. you're actually dding those value to your screen. By the same logic, if you blast nothing but NULL to this file. Well, your screen will be black ;)
And, of course I think I answered the wrong question,. e.g. one you did not ask. So if I now understand your statement correctly there. It would seem like someone's math is wrong. Perhaps in the frame buffer driver for this hardware. -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CALHSORqqp_-X33deSWd1mpzt74KjrwOgpsgQPHM1jzpKYkD48Q%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
