Vladimir Prus wrote:
Joel de Guzman wrote:
Vladimir Prus wrote:
I'm trying to say that the choice of coordinate unit -- pixel, millimeter, inch, whatever, is only important if you need to write:
window.setWidth(10cm);
and in a proper GUI library you should never set width to absolute value like that. Instead, you should do:
window.setWidth(screen_width()*some_constant);
In that case "screen_width()" can return SomeVeryOpaqueType that you can multiply by float, but can't convert to pixel, or to to inch, or to anything else.
Hmmmm....
I'm not sure about this. Say for example that I am writing a WYSIWYG CAD application and I'd like to draw vertical and horizontal rulers. At 100% page view, I'd like the ruler to be a 1:1 with the actual screen at the designated resolution (say 72 DPI). How would I draw my ruler if the coordinates are abstracted in terms of percentage?
You mean the the rule has millimeters as the unit an at 1:1 zoom you want 1 millimeter of the ruler to be 1 millimeter on the screen? Then yes, you'll need some way to convert millimetres to units used on screen. Though I don't understand why you want such strict equality. You won't measure distances on the screen with a physical ruler anyway, right?
Why not ;-) ? Replace "screen" with "paper" and you'll want to have accurate 1:1 layouts. This is the very essence of device independence. If, say, I want to print a PCB (printed circuit board) on a 300DPI laser printer, I'd want absolute accuracy, otherwise, my components will not fit the holes. Device independence means that both "screen" and "paper" should behave identically. If I want 10cm on paper how can I create such a thing in an abstracted relative coordinate system? Bottom line: you'll want both absolute and relative dimensions. Cheers, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net