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ATI Catalyst + Projector = unreadable small fonts

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  • ATI Catalyst + Projector = unreadable small fonts

    I have the problem with fglrx driver and my projector for years (so it happend with various Suse and fglrx versions).

    When I boot my pc with the projector connected (DVI), the fonts in KDE are too small to be read (I guess 3 pixels high). Even if the projetor is switched off, my 19" TFT (also DVI connection) shows the small fonts. Plugging TFT and projector to the other DVI connector of the ATI card doesn't change anything.
    It only seems to help when I insert the line "DisplaySize 376 301" to my xorg.conf. (my 19" TFT is 376mm wide and 301mm high)
    So it seems to me, the fglrx driver thinks my screen is 4 meters wide and adjusts the font size accordingly. Why does the driver change the fonts at all? Is this a wanted behaviour? I would call it a bug.


    Intel Quadcore, OpenSuse 11.1 64Bit
    ATI 3850, Catalyst 9.2
    NEC 1980FXi 19" TFT
    Sanyo Z3 LCD projector

  • #2
    Can you pastebin your xorg log so we can see what display size the projector is providing via EDID ?

    I'm not 100% sure how X handles having different DPI on the displays but my recollection is that the randr model assumes the same DPI for both displays, so whatever screen comes up first probably sets the DPI for both.
    Last edited by bridgman; 03-08-2009, 06:06 PM.


    • #3
      Sorry for the messed up xorg.conf file. I didn't clean it up yet.


      • #4
        I got a similar problem with the Catalyst Control Center using XFCE with Ubuntu 8.10, font are unreadable on 1980x1080 42" tv. I increased font size of others programs / XFCE really better now... except CCC that I cannot change.


        • #5
          Yeah, connecting the projector is pure horror. CCC is not usable with this small font and I cannot navigate through it blindly.

          But hopefully someone from ATI reports back to tell whats going on there.


          • #6
            Still waiting for your log file.


            • #7
              Originally posted by bridgman View Post
              Still waiting for your log file.
              Sorry for that. Thought you want my xorg.conf.
              Will post it in 12h when I'm at home again.


              • #8
                I had to add a line to my Section "Monitor". That is how it looks now:
                Section "Monitor"
                        DisplaySize 517   325   # mm
                        Identifier  "Monitor0"
                        VendorName  "DEL"
                        ModelName   "DELL 2405FPW"
                        HorizSync   30.0 - 81.0
                        VertRefresh 56.0 - 76.0
                        Option  "DPMS"
                With this I get some nice looking fonts on my 1920x1200 screen. You most likely can use the exact same values for your 42" TV, too. That is I had to add the "DisplaySize" line when I also plugged in my 40" LCD TV since it somehow overrides the settings without such a line. with it, everything is perfect here.


                • #9
                  This is my /var/log/Xorg.0.log without the projector connected.

                  And now the log file after connecting the (always switched off) projector and rebooting Suse 11.1

                  Ok, the EDID of the projector says it's 160cm wide and 90cm high. But who calculates the tiny font size out of these numbers? Is it the fglrx driver or Xorg?
                  Last edited by mibo; 03-10-2009, 05:26 PM.


                  • #10
                    This is xorg. I have the same problem with open drivers, too.


                    • #11
                      So I have to complain in the xorg forum and not in the ATI forum? bridgman?


                      • #12
                        What's missing from the current EDID info (or any other input to xorg) is any concept of viewing distance. Even a heuristic to maintain a minimum point size (character size in pixels, roughly) probably wouldn't do what you want since that would put a floor at minimum readability and you probably want "nice" readability.

                        So yeah, xorg would be the group to talk to, although "complain" is a bit strong since the server is doing the calculations correctly based on the info provided by the monitor (which is also reasonably correct). You will be asking for some kind of over-ride to say "pretend my projector didn't just tell you about the big screen".

                        Leaving a DisplaySize line in your Monitor section seems like a decent solution for now, so you might want to word your question "if xorg.conf is going away how will this be handled in the future, huh ? huh ?".


                        • #13
                          Hmm, I see your point.
                          But, lets see it from a "stupid user's" (my) perspective.
                          When I connect the projector to my PC running Windows XP - the font size stays the same and is readable ;-)

                          But maybe I'll ask the xorg guys about the font size...

                          Thanks for your help!


                          • #14
                            Yeah, but if you wanted Windows behaviour everywhere you would probably be using Windows

                            AFAIK Windows does not consider DPI when converting character sizes from points to pixels. This avoids the problem you are experiencing, but brings a number of *different* problems (eg fonts becoming unreadable on a laptop with a small, high resolution LCD).

                            Be aware that this issue is still being hotly debated on xorg lists, and that there are a number of conflicting views on what "correct" behaviour really is.

                            It seems to me that none of the current approaches deliver what a user really expects when they get a new, high res monitor, which IMO is a combination of "seeing more" and "clearer text". This implies that neither ignoring DPI (Windows) or calculating based on DPI (X) is correct and that the ideal behaviour would be some kind of pro-rated calculation where doubling the DPI might result in fonts which are maybe 1.5 times as big when measured in pixels -- smaller than before but still readable.