On Tue, 19 Aug 2003, Alex Deucher wrote:
> How is DPI supposed to work if you have a virtual desktop larger than
> the current mode? the current code seems to produce the wrong DPI.
> xf86SetDpi() has the following code:
>
> if (pScrn->widthmm > 0) {
> pScrn->xDpi =
> (int)((double)pScrn->virtualX * MMPERINCH / pScrn->widthmm);
> }
> if (pScrn->heightmm > 0) {
> pScrn->yDpi =
> (int)((double)pScrn->virtualY * MMPERINCH / pScrn->heightmm);
> }
>
> if you have, for example,
> DisplaySize 300 230
> and a virtual resolution of say 2048x768 and a mode of 1024x768, the
> DPI would get set to 173, 84. which (I think) is wrong. it should be
> 86, 84 which is what you would get when your mode matches your virtual
> resolution. I'm having the same problem with Mergedfb since it uses a
> virtual resolution with two viewports looking into it. I could add the
> heightmm or widthmm of both heads to make the DPI "correct" for the
> virtual size with respect to the two heads. I'm not sure how xinerama
> deals with it. maybe the current behavior is right? I dunno.
PanoramiXCreateConnectionBlock() in xc/programs/Xserver/Xext/panoramiX.c
has:
/*
* OK, change some dimensions so it looks as if it were one big screen
*/
old_width = root->pixWidth;
old_height = root->pixHeight;
root->pixWidth = PanoramiXPixWidth;
root->pixHeight = PanoramiXPixHeight;
width_mult = (1.0 * root->pixWidth) / old_width;
height_mult = (1.0 * root->pixHeight) / old_height;
root->mmWidth *= width_mult;
root->mmHeight *= height_mult;
which adjusts mmWidth and mmHeight in the manner you are proposing.
mmWidth becomes pScrn->widthmm inside xf86SetDpi().
--
Andrew C Aitchison
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