Why EDID is not trustworthy for DPI

Matthew Garrett mjg59 at srcf.ucam.org
Thu Oct 6 13:37:43 UTC 2011

On Thu, Oct 06, 2011 at 01:13:21PM +0200, Nicolas Mailhot wrote:
> Le Mer 5 octobre 2011 23:35, Matthew Garrett a écrit :
> > This... works badly. Really. Open gimp and add some text. Now double the
> > size of the font. Save the image and open it in image viewer, and zoom
> > out so the text is half the size. It doesn't look the same as your
> > original text.
> >
> > Rendering fonts (and even SVGs) well requires you to know the scale that
> > you're rendering to. More pixels mean you can add more detail. If you
> > shrink that then the additional detail is still there, getting in the
> > way of the actually important information. Doing this properly requires
> > that the original object renderer be part of the scaling process, and
> > doing that on the fly with reasonable performance just isn't part of our
> > rendering stack at the moment.
> Which is exactly why forcing 96dpi on displays which have very different pixel
> densities *today* is not a good idea at all.

Knowing the number of pixels available means that the output will be 
legible, even if you'd prefer it to be a different size. Rescaling after 
rendering means that the output will be illegible, even if it's the 
correct size. Given that we don't have the ability to dynamically 
re-render everything the moment an application is moved between screens, 
what's your proposed solution?

Matthew Garrett | mjg59 at srcf.ucam.org

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