Re: Geometry problem

[Richard Frith-Macdonald]

On Tuesday, June 24, 2003, at 04:17  am, Kazunobu Kuriyama wrote:

> Hi, all.
>
> I have a question about the GNUstep's geometry.
> The question is as follows:
>
>
>        X
>    |-------|    Object A
> -- +---------------------------------------------------
>  | |(0,0)
> Y | |
>  | |            Object B
> -- |       +----------------------------------------
>    |       |(X,Y)
>    |       |
>    |       |
>    |       |
>
>
> Here, you have two GUI objects Object A and Object B.  Object A
> is the main window of an GNUstep application, and Object B is an
> instance of either the NSView class or its subclass.  The coordinates
> system is taken as shown above.

Actually, the direction of increasing Y is upwards (unless you are in a 
flipped view).

>  Ignore the border width for now
> because it's a matter of arithmetic.  Then, you need to know the
> coordinates values (X, Y) to implement a method declared in the
> interface of Object B.  Write a piece of code to calculate X and Y.
> The code should be independent of the underlying window system.

I don't understand what you mean.
The coordinates of Object B (an NSView) within the coordinate system of 
the enclosing ObjectA (an NSWindow), are obtained using the -frame 
method.
eg.

  NSRect bFrame = [B frame];
  NSLog(@"Position ... x: %f, y: %f", bFrame.origin.x, bFrame.origin.y);


To convert from the local coordinate system (of object A) to the screen 
coordinate system, you use the NSWindow method -convertBaseToScreen:

eg.

  NSPoint p = [A convertBaseToScreen: bFrame.origin];


> If Object A is a parent or ancestor of Object B (in a sense of
> window hierarchy), the answer may be easy.  I have no idea,
> however, if Object A is an instance of NSApplication.

It isn't.

> Could you help me so that I won't devise GSTranslateCoordinates,
> a ridiculous wrapper of XTranslateCoordinates() that ruins
> the GNUstep's OO structure?

I'm not sure you could wrap XTranslateCoordinates() in such a way that 
it could meaningfully work within the GNUstep coordinates system... all 
mappingss betwween X coordinates and GNUstep coordinates are hidden in 
the backend library and GNUstep user code should never have anything to 
do with them.