Re: Coordinate system

[Alexander Malmberg]

Stefan Urbanek wrote:
> 
> Hi,
> 
> I am confused. What is the coordinate system for drawing
> in gnustep? Is it pixels or points? Or is it pixels on screen
> and points on PostScript output?

Points, always. ((Well, the default matrix is such that one unit in user
space is one point; you can change this so one unit is one mm, or one
meter, or anything else that you can get as a multiple of a point. There
is no way to get at device pixels through the dps interface.))

All(?) current backends assume that the display is 72dpi, so that 1
pixel==1 point, but this is an implementation limitation. back-art has
no problems rendering at other resolutions, but we'd still need to fix
back/Source/x11/* to convert sizes and coordinates of events and windows
between points and pixels.

[snip]
> Another problem should be drawing between pixels, but this can
> be solved by rounding to integer values in backend.

Handling this is up to the backend. back-art can do (and, currently,
always does) subpixel rendering. When clarity is more important than
accurate rendering, you use strokeadjust (not implemented in back-art)
and screen fonts (implemented in back-art).

- Alexander Malmberg