Re: [boost] GUI coordinate units (Was: GUI foundations)

From: Stefan Seefeld (seefeld_at_[hidden])
Date: 2005-10-05 09:51:23

Vladimir Prus wrote:
> Stefan Seefeld wrote:
> 
> 
>>>Then I don't understand what you said before. You said you expect that
>>>printing of portion of screen should preserve dimenstions. Do you mean
>>>dimensions in millmeters or in what unit? And why do you expect for them
>>>to be preserved on paper?
>>
>>Yes, I'm talking about physical dimensions (millimeters, whatever). Why
>>should I *not* expect it to preserve its size ?
> 
> 
> Whenever I print a web page, the width of paper is different from the
> browser window width.

Indeed, which makes designing web sites particularly challenging. However,
web sites typically contain a lot of text, which can be reflown to fit on
different media, so here, too, the solution is to use layout, not scale.

>>Let me rephrase that a bit: the application asks the display server
>>for a region of suitable size, such that all it wants to draw will fit in.
>>This size requirement will be a fuction of the size of the graphical
>>elements they lay inside (and, I reiterate, which generally should have
>>physical dimensions).
> 
> 
> Say, scrollbar is 5mm on my screen. Will that be good on a handheld
> computer? I doubt that. And how do you determine preferred physical size of
> scrollbar? Should it be 10cm or 5mm? You can't answer this question without
> knows the size of the drawing surface, so maybe scrollbar width should
> drawing_surface_width*some_fraction

You raise interesting questions. I think it is an error to try to solve
the challenge to design a GUI for different output media (devices) in terms
of scale. It is not because you scale your widgets down that you make a
graphical application usable on a PDA. Rather, the GUI 'style' should be
adapted to the output device in that case.
This is another argument for applications not to rely on a particular
GUI style, at least not if they are meant to be portable across devices.
High-resolution devices could use a GUI with much more detail than low-resolution
devices. I'd even go further and try to abstract away much of the widgetry
into high-level 'tasklets' that can be implemented specifically for particular
output- (and input-, i.e. mouse, pen, keyboard, glove, etc.) devices.
If a user's GUI can be described semantically in terms of 'tasks', its GUI
can be much more flexibly replaced to adjust to particular hardware.
But that gets us into quite a different discussion.

> Yes, but what does that prove? The preferred size of text is set by the
> user, who certainly cares only about physical size, but on a specific
> monitor. If he buys a different monitor with different size and resolution,
> it's not at all clear he'll want to retain the same physical size of the
> text. He might want to make it large, or smaller, depending on preferences. 

Quite right. Yet, it is the user, and he would rather think about size,
not resolution. :-)

> Going back to scrollbar -- I think it's width should also be customisable by
> the user vis some config tool. And if user hasn't specified anything,
> percentage of screen width looks better to me than any "natural" 5mm. Any
> constant you'll hardcode will be just that -- hardcoded constant.

Well, it's a constant in the context of a GUI style. You can still
a) replace / modify the style
b) scale a graphic to zoom in / out

Regards,
                Stefan