X server display buffer

solov · 2014-12-19 07:43:30

hello, i am not sure how x is working, but could it be possible to get the X display buffer (doubleBuffer?) memory pointer??? i want to pass the display buffer to some custom hw that will render it...
i can do it with my hw on some picture i put in memory and it is working , but i want to do it on the X display.
thanks a log!!!

drcouzelis · 2014-12-21 01:01:46

I don't understand. Your question seems pretty vague.

Is this a programming question? What is the custom hardware? Can you please post your code?

Last edited by drcouzelis (2014-12-21 01:02:09)

solov · 2014-12-21 06:03:34

sorry,will try to expain better.
i have some hwBoard powered by linux. it have an fpga hw that can fetch buffers from the ram and display them on hdmi output (no video card is presents - only the fpga can render). Can i have the x server buffer/pointer to buffer/ on the ram so i can pass it to the display. The format of the data will be my consern , i just need to have the X server display data at hand... thanks a lot!

Trilby · 2014-12-21 12:42:19

I'm not sure that there is any full screen buffer in regular ram prior to the gpu (unless you use vesa or fbdev). So the actual memory address will be hardware specific.

Even if you get a pointer to the memory location by researching the hardware, you will have no way of knowing when a frame is complete and/or when it is safe to read.

Essentially what you are trying to do is probably harder than writing a graphics driver: you have to write the equivalent of a graphics driver that will communicate and cooperate with every other graphics card and driver out there.

What you may be able to do is get a copy of the current screen from X, then display this somewhere else. But this would be exceedingly slow and resource-demanding - it likely could not run in real time.

Based on the little you have told us about the goal, your best bet would likely be in configuring or hacking fbdev to write to a memory location of your chosing.

EDIT: after rereading the question, my last sentence is probably the only one that applies. If you are not using a video driver then there is no display buffer. X communicates with a video driver and the driver may be the only thing that ever creates a buffer of what is actually on screen. You probably don't want to have one driver render to memory then try to copy and translate that buffer to your device - this would be very slow and you'd run into issues of knowing when a frame could be copied. You just need a driver to write the completed frames to your device. So you need to create a video driver for your device - again looking at fbdev code would likely be the way to go.

Last edited by Trilby (2014-12-21 13:10:45)

solov · 2014-12-21 19:02:33

thanks a lot...will try this.will report with progress/success...

ewaller · 2014-12-21 19:17:54

Sounds like a project I was involved with a few years ago based on a DaVinci processor http://www.ti.com/lsds/ti/dsp/video_pro … rview.page

... Which leads me to ask... Is this an Arch question, or is an Arch Arm question? If it is an Arm system, you might get a better answer on the Arch Arm forums.

solov · 2014-12-21 19:24:20

it is arm/x/linux/i need some starting point issue...
if u will see http://wiki.analog.com/_detail/resource … %3Aadv7511
this is the embedded board i play with; and is somehow transfer x display to some hw and display;
i am trying to play with this hw and the fpga to add more real time display on top of the x display; i can do this by rendering data from the ram (which is common to the linux and the fpga) so i need somehow to add the x buffer to this ram...

Arch Linux

#1 2014-12-19 07:43:30

X server display buffer

#2 2014-12-21 01:01:46

Re: X server display buffer

#3 2014-12-21 06:03:34

Re: X server display buffer

#4 2014-12-21 12:42:19

Re: X server display buffer

#5 2014-12-21 19:02:33

Re: X server display buffer

#6 2014-12-21 19:17:54

Re: X server display buffer

#7 2014-12-21 19:24:20

Re: X server display buffer

Board footer