xrandr reports screen dimensions as 0mm x 0mm

[totaam]

Issue migrated from trac ticket # 728

component: server | priority: critical | resolution: wontfix | keywords: dummy randr x11

2014-11-04 07:46:52: totaam created the issue

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$ xrandr 
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 320 x 175, current 2560 x 1600, maximum 8192 x 4096
default connected 2560x1600+0+0 0mm x 0mm

[totaam]

2014-11-05 03:11:13: totaam changed status from new to assigned

[totaam]

2014-11-05 03:11:13: totaam changed owner from antoine to totaam

[totaam]

2014-11-05 03:11:13: totaam commented

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The code that prints this is is in xrandr.c

if (cur_mode)
{
    printf (" %dmm x %dmm",
	(int)output_info->mm_width, (int)output_info->mm_height);
}

With:

get_screen (current);
get_crtcs ();
get_outputs ();
(..)
for (output # all_outputs; output; outputoutput->next)
{
    XRROutputInfo   *output_info = output->output_info;
(..)

And we have in get_outputs() the core of it, which populates the all_outputs global, a linked list (see all_outputs_tail) of all outputs:

for (o = 0; o < res->noutput; o++)
{
    XRROutputInfo   *output_info = XRRGetOutputInfo (dpy, res, res->outputs[o]);

noutput is set in crtc_add_output:

crtc_add_output (crtc_t *crtc, output_t *output)

Which is called from set_crtcs:

for (output # all_outputs; output; outputoutput->next)
{
    if (!output->mode_info) continue;
    crtc_add_output (output->crtc_info, output);
}

So, it looks like we need to ensure XRROutputInfo is populated correctly. Here it is:

typedef struct _XRROutputInfo {
    Time	    timestamp;
    RRCrtc	    crtc;
    char	    *name;
    int		    nameLen;
    unsigned long   mm_width;
    unsigned long   mm_height;
    Connection	    connection;
    SubpixelOrder   subpixel_order;
    int		    ncrtc;
    RRCrtc	    *crtcs;
    int		    nclone;
    RROutput	    *clones;
    int		    nmode;
    int		    npreferred;
    RRMode	    *modes;
} XRROutputInfo;

It is interesting to see subpixel_order is in there too. Maybe we should add another window property to allow us to change this on the fly (see #559) as there is bound to be software out there that does not use the standard way of figuring out the pixel order and will use hardware calls instead.

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We may also want to deal with the gamma warning, which comes from:

size = XRRGetCrtcGammaSize(dpy, output->crtc_info->crtc.xid);
if (!size) {
    warning("Failed to get size of gamma for output %s\n", output->output.string);
    return;
}

This should be simple enough:

typedef struct _XRRCrtcGamma {
    int		    size;
    unsigned short  *red;
    unsigned short  *green;
    unsigned short  *blue;
} XRRCrtcGamma;

Which is returned by:

XRRCrtcGamma *
XRRGetCrtcGamma (Display *dpy, RRCrtc crtc);

I don't think we want to do any gamma correction on the server. The client will do it already when rendering the output.
Would be easy to add if we need it.

[totaam]

2014-11-05 07:55:51: totaam uploaded file dummy_driver.c (24.3 KiB)

modified dummy driver which dumps a lot more information about internal data structures

[totaam]

2014-11-06 06:47:41: totaam commented

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Following the work on #349, down the rabbit hole we go..

XRRGetOutputInfo is from libXRandR, it gets the mm dimensions from the xRRGetOutputInfoReply response to a RRGetOutputInfo X11 server call (subpixelOrder is in there too).

The server populates xRRGetOutputInfoReply from the RROutputPtr it gets using the VERIFY_RR_OUTPUT macro..
RROutputPtr is a pointer to RROutputRec (aka _rrOutput) which has more or less the same data in it, including mm and subpixel order.
The only place the server creates RROutputRec is in RROutputCreate.
But when I dump the outputs in the dummy driver, there aren't any! And if I add one using:

output = RROutputCreate(pScrn->pScreen, "default", 7, NULL);
output->mmWidth = pScrn->pScreen->mmWidth;
output->mmHeight = pScrn->pScreen->mmHeight;

It shows the output (and more warnings about missing modes for the output):

dummy connected 2560x1600+0+0 (0x55) normal (normal) 677mm x 423mm

but the mm stays at 0...

In the end, I think the "default" output we see is a virtual one. Created where?

I give up. For now.

[totaam]

2014-11-06 07:30:17: totaam uploaded file dummy_driver.2.c (28.2 KiB)

hacked driver with lots of unsuccessful changes to try to figure out what we need to do

[totaam]

2015-01-26 08:54:34: totaam commented

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Re-scheduling, see #56#comment:9

[totaam]

2015-10-23 07:10:25: antoine commented

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No movement on this upstream, re-scheduling.

[totaam]

2016-07-12 17:51:51: antoine commented

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Milestone renamed

[totaam]

2016-08-21 10:55:50: antoine commented

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Milestone renamed

[totaam]

2017-02-16 04:38:22: antoine changed status from assigned to closed

[totaam]

2017-02-16 04:38:22: antoine set resolution to wontfix

[totaam]

2017-02-16 04:38:22: antoine commented

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Best to deal with this in #56