Re: [Gtk2hs-devel] patches: GDK_CURRENT_TIME, Gdk Cursor, Pointer and Keyboard grabbing

[Axel S. <Axe...@en...>]

Hi Bit,

On Tue, 2007-11-20 at 19:33 +0200, Bit Connor wrote:
> > Applied. Thanks for the good documentation. One question about the
> > functions that get the screen width and height in pixels: Don't these
> > functions take a display (which we haven't bound yet)?
> 
> These functions do not take a display. They all have the same prototype:
> 
>   gint gdk_screen_width(void);
> 
> You can see for yourself in the header gdk/gdk.h or in the online docs:
> 
>   http://www.gtk.org/api/2.6/gdk/gdk-General.html#gdk-screen-width
> 
> For interested parties, the functions return the dimensions of the
> default screen. Here is the source for gdk_screen_width:
> 
>   gint
>   gdk_screen_width (void)
>   {
>     return gdk_screen_get_width (gdk_screen_get_default());
>   }
> 
> It would be useful to add bindings to GtkDisplay and GtkScreen, for
> those who need the added control.

Ok, then that's fine then.

>  Maybe I will even be up to the task.
> But first I would like to finish the bindings for GtkCursor. Which
> brings me to a question. A while ago someone asked on the gtk2hs-users
> mailing list how to change the cursor to an hourglass. The best way to
> do this is to use the function gdk_cursor_new to create the hourglass
> cursor, with an argument of GDK_WATCH, which is a value of the
> GdkCursorType enum.
> 
> My question is what is the best way to do the bindings for the
> GdkCursorType enum?
> 
> It looks like:
> 
>   typedef enum
>   {
>     GDK_X_CURSOR 		  = 0,
>     GDK_ARROW 		  = 2,
>     GDK_BASED_ARROW_DOWN    = 4,
>     GDK_BASED_ARROW_UP 	  = 6,
>     /* ... */
>     /* Lots more! */
>     /* ... */
>     GDK_UR_ANGLE 		  = 148,
>     GDK_WATCH 		  = 150,
>     GDK_XTERM 		  = 152,
>     GDK_LAST_CURSOR,
>     GDK_CURSOR_IS_PIXMAP 	= -1
>   } GdkCursorType;
> 
> When I tried binding this enum in the same way that all the other
> enums are done in gtk2hs, then the resulting haskell type was:
> 
>   data CursorType = XCursor | Arrow | BasedArrowDown | BasedArrowUp |
> {- lots more -} | UrAngle | Watch | Xterm | LastCursor |
> CursorIsPixmap
> 
> These constructors don't seem to fit in with the rest of the gtk2hs
> api since they have no namespace-like prefix. I can think of two
> alternatives:
> 
> 1. Figure out a way to add a namespace-like prefix to the
> constructors, so that instead of XCursor, we will have
> CursorTypeXCursor

You can do this with c2hs. There are two options:

a) you can rename individual values
{#enum GdkCursor { GDK_UR_ARROW as CurUrArrow } #}

b) you can add a prefix
{#enum GdkCursor with prefix = Cur #}

You can also use both. The stupid thing is that you can't omit certain
values (such as GdkLastCursor and GdkCursorIsPixmap).

You could also put this enumeration into a separate module that is not
exported by default. The user can then import this module qualified.

> 2. Don't have a haskell type for GdkCursorType, and instead use a
> string where a GdkCursorType would be used, so that instead of
> XCursor, we will have "X_CURSOR", or some other variation. This is
> similar to the way gtk2hs works with KeySyms.

I think you should not use strings in this case by numeric constants:

type Cursor = ...whatever...

cursorUrArrow :: Cursor
cursorUrArrow = {#const GDK_UR_ARROW #}

You might want to look into .../General/Structs.hsc where we use hsc2hs
to infer constants like these.

I guess it boils down to if the cursor enumeration is extensible. If it
is, it's better to define numeric constants since a Haskell enumeration
is quite final, unless you add a 

data Cursor
  = ..
  | ..
  | CurUser Int

This solution is a bit unfortunate in this case, as you can't use c2hs
to do this for you and you have to define the whole enumeration by hand.

I think 2. with constants is the way in this case.

Cheers,
Axel.