GCompris in sugar ?

Adam Jackson ajackson at redhat.com
Wed Jan 31 18:22:01 EST 2007

On Wed, 2007-01-31 at 23:42 +0100, Yves Combe wrote:
> Hello,
> I am part of the GCompris developper team, we looked at the technical
> issues involved to provide an OLPC version.
> Indeed, i don't know what exactly is the OLPC specification.
> We use an 800x600 display. I know OLPC is 1900x1200 in B&W mode, how
> much is it in colors ? it will need some work to check GCompris can
> display correctly in B&W (easy but long), and  to change it's size if
> needed (easy with zooming in gnomecanvas).

1200x900.  And since you brought it up, I'd like to dispel a myth.

It's not like your pixels suddenly get larger in gray mode, the dots
stay the same size.  You just lose chromaticity, so you need to make
sure your colors are still discernable even when just looking at
luminance.  (And yes, it's pretty much the NTSC luminance formula.)

Likewise, there's really no point in adjusting font sizes when changing
from one mode to the other.  There's a minimum size for legibility, and
it's about the same on the XO screen regardless of whether they're
colored or gray pixels.  This minimum size may be slightly smaller on
the XO screen than compared to a normal 100dpi LCD, but not by much, at
least when measured in points.

And of course, don't size your fonts in pixels, because that's Bad And

If you like you can even do the math.  OLPC use for a child will be
about 200dpi at 18"; one degree of arc would be about 0.314" of screen,
or 62.8 dots (18 inch * tan(1 deg) * 200 dots per inch).  Typical 100dpi
use for an adult is about 24" to 30", which is 41.9 to 52.4 dots per
degree.  So your fonts need to be anywhere between 20% and 50% bigger,
in points, to be the same perceptual size in arc sweep.  And since most
text is high-contrast, you can aim for the low end of that range, since
you'll be gaining in dots per unit arc.  But by this same principle,
you're not going to see much effective resolution change for text when
going from color to grayscale, so there's no real need to change font
size when that occurs.

And a good thing too, since I don't believe that event goes out on dbus.

This goes for the rest of the UI too, though there's some nonlinearity
involved due to the color sampling at small sizes.  16 pixel square
icons won't work, but 64^2 might still look reasonable.  The big thing
if you want grayscale mode to work is to pick colors with different

- ajax

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