Why EDID is not trustworthy for DPI

Matthew Garrett mjg59 at srcf.ucam.org
Wed Oct 5 21:35:58 UTC 2011

On Wed, Oct 05, 2011 at 11:11:38PM +0200, Benny Amorsen wrote:
> Matthew Garrett <mjg59 at srcf.ucam.org> writes:
> > We have no technological solution for dealing with the fact that 
> > applications may move from one DPI to another at runtime, and may even 
> > be displaying on both displays at once.
> >From a technology viewpoint, that is actually theoretically easy to
> handle on modern hardware: Render everything as 3D objects and let the
> graphics hardware scale as appropriate.

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.

Matthew Garrett | mjg59 at srcf.ucam.org

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