Writing to the Framebuffer
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Writing to the Framebuffer
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Re: Writing to the Framebuffer
#2The reason why sudo wasn't working is that it runs the command with root privileges, but redirecting to a file with > is done through the shell, which is running under your normal user level privileges. If you want to redirect to a file that only root can write to, you can use the tee command. That command will write anything passed to it via stdin to the file given as an arg.
For example, echo "foo" | sudo tee /path/to/file
or any of the other ways listed here: https://stackoverflow.com/questions/82256/how-do-i-use-sudo-...
Re: Writing to the Framebuffer
#3The reason why sudo wasn't working is that it runs the command with root privileges, but redirecting to a file with > is done through the shell, which is running under your normal user level privileges. If you want to redirect to a file that only root can write to, you can use the tee command. That command will write anything passed to it via stdin to the file given as an arg. For example, echo "foo" | sudo tee /path…
tee also prints to standard output, so I'd suggest piping to /dev/null if you're going to produce a lot of output.
Re: Writing to the Framebuffer
#4The reason why sudo wasn't working is that it runs the command with root privileges, but redirecting to a file with > is done through the shell, which is running under your normal user level privileges. If you want to redirect to a file that only root can write to, you can use the tee command. That command will write anything passed to it via stdin to the file given as an arg. For example, echo "foo" | sudo tee /path…
Or you can add your user to the `video` group.
EDIT: it says so in TFA. Oops!
Re: Writing to the Framebuffer
#5There may be more than just one simultaneous framebuffer per display on the hardware level.
GPUs can actually scan to a display from multiple overlapping framebuffers in different resolutions and color formats in the same time. Alpha blending and rotations are often supported as well.
A bit like a very large mouse cursor. In a way, mouse cursors are also framebuffers. Or like hardware video layers in the nineties.
Re: Writing to the Framebuffer
#6Is /dev/fb writing directly to the framebuffer or is there translation going on kernel side? Is the card in VESA / BIOS mode when on a virtual console without X?
Re: Writing to the Framebuffer
#7> one horizontal line at a time, with one byte for Blue,Green,Red,Alpha(?) per pixel (seems like 24-bit true color).
You can (and should if you are writing software not only for yourself) ask the kernel about the framebuffer layout using FBIOGET_FSCREENINFO and FBIOGET_VSCREENINFO ioctls.
Re: Writing to the Framebuffer
#8There may be more than just one simultaneous framebuffer per display on the hardware level. GPUs can actually scan to a display from multiple overlapping framebuffers in different resolutions and color formats in the same time . Alpha blending and rotations are often supported as well. A bit like a very large mouse cursor. In a way, mouse cursors are also framebuffers. Or like hardware video layers in the nineties.
Eh, it's a handy abstraction. There's also no uniform memory space (multiple RAM chips, virtual memory, swap), CPUs absolutely are not the "run one opcode after another" thing that programmers pretend, and by the time you stream HTML from a server to client it's been sliced into a thousand pieces, compressed, encrypted, reordered...
We like abstractions.
Re: Writing to the Framebuffer
#9Is /dev/fb writing directly to the framebuffer or is there translation going on kernel side? Is the card in VESA / BIOS mode when on a virtual console without X?
I think the kernel docs[0] indicate that it's a kernel-managed abstraction?
[0] https://www.kernel.org/doc/Documentation/fb/framebuffer.txt
Re: Writing to the Framebuffer
#10I wonder if there's a way to take over another VT so you don't have the console text over your images.