[m-rev.] Xlib interface for extras

[Ian MacLarty]

> I've been writing a little Xlib based graphics library off and on for a
> couple of months and would like to add it to extras.
>
> Feedback gratefully received, as would be flashier applications.
>

This looks neat.  It also seems to work fine on Max OS X (I tested it).

> % easyx.m
> % Ralph Becket <rafe at cs.mu.oz.au>
> % Fri Jun 25 17:49:48 EST 2004
> %
> % A simple, easy-to-use wrapper around some of Xlib, good for putting
> % lines and boxes on the screen and writing simple interactive  
> graphical
> % applications.  This library aims for ease of use over efficiency.
> %
> % All drawing is done to a backing pixmap and the user must explicitly  
> call
> % easyx.flush/3 to make visible any changes since the last call to
> % easyx.flush/3.  Repainting after exposure events is handled  
> automatically,
> % although resizing the window does require the user to redraw.
> %
> % An abstract coordinate space is used, but in keeping with Xlib, the
> % origin of the coordinate space is at the top-left of a window, with
> % coordinates increasing down and to the right.  An abstract coordinate
> % value of 1.0 corresponds to the shorter of the current width or  
> height
> % of the window.
> %
> % Angles, where used, are measured in radians.

Personally I'd find degrees easier to use.  I find 45.0 is easier to  
read than math.pi/4.0 - especially for this type of simple library.

>     % One must open a display in order to create a window.
>     %
> :- type display == xlib.display_ptr.

Why is this not an abstract type?

>
>     % open_display(Display, !IO)
>     % Open a connection to the default display.
>     %
> :- pred open_display(display::out, io::di, io::uo) is det.
>
>     % open_display(DisplayName, Display, !IO)
>     % Open a connection to the named display.
>     %
> :- pred open_display(string::in, display::out, io::di, io::uo) is det.
>
>
>     % A window is a target for drawing operations and a source of
>     % input events (mouse and keyboard etc.)
>     %
> :- type window.
>
>     % create_window(Display, Title, Width, Height, Orientation,  
> Window, !IO)
>     % Create Window on Display, with the given Title, Width, Height and
>     % Orientation.
>     %
> :- pred create_window(display::in, string::in, int::in, int::in,
>             window::out, io::di, io::uo) is det.
>

The orientation argument seems to have been left out here.

>     % flush(Window, !IO)
>     % Make all rendering to Window since the last call to flush/3  
> visible
>     % (all rendering is done to a separate drawing area; this predicate
>     % updates what is on the screen.)
>     %
> :- pred flush(window::in, io::di, io::uo) is det.
>
>     % clear_window(Window, !IO)
>     % Clear the window using the current colour.
>     %
> :- pred clear_window(window::in, io::di, io::uo) is det.
>
>
> :- type font == xlib.font_struct_ptr.
>

Couldn't font be an abstract type?

>     % load_font(Window, FontName, Font, !IO)
>     % Load a font from the X server.
>     %
> :- pred load_font(window::in, string::in, font::out, io::di, io::uo)  
> is det.
>
>     % Set the font for drawing text.
>     %
> :- pred set_font(window::in, font::in, io::di, io::uo) is det.
>
>
> :- type colour == xlib.color_ptr.

Again couldn't this be abstract?

...
>
>
>     % The left hand mouse button is usually number 1.
>     %
> :- type button == int.

What about making this button1 ; button2 ; button3  or even left ;  
middle ; right?  This might be useful when constructing switches on  
which button was pressed.  Also a button variable having the value 999  
is pretty meaningless.

...
> xlib.m:
> %---------------------------------------------------------------------- 
> -------%
> % Copyright (C) 2004 The University of Melbourne.
> % This file may only be copied under the terms of the GNU Library  
> General
> % Public License - see the file COPYING.LIB in the Mercury  
> distribution.
> % vim: ft=mercury ts=4 sw=4 et wm=0 tw=0
> %---------------------------------------------------------------------- 
> -------%
> % xlib.m
> % Ralph Becket <rafe at cs.mu.oz.au>
> % Mon Jun 21 17:48:24 EST 2004
> %
> % A low-level interface to parts of Xlib (this is very little more  
> than a
> % few useful symbol definitions and wrappers around various Xlib  
> calls.)
> %
> %---------------------------------------------------------------------- 
> -------%
>
> :- module xlib.
>
> :- interface.
>
> :- import_module list.
>
>
>
> :- type display_ptr.
>
> :- impure func open_display = (display_ptr::out) is semidet.
>
> :- impure func open_display(string::in) = (display_ptr::out) is  
> semidet.
>
> :- impure pred flush(display_ptr::in) is det.
>
> :- impure pred sync(display_ptr::in) is det.
>

Why don't you make these pure and thread the IO state?  The semidet  
ones you can make det by getting them to return a bool, so you can then  
thread the IO state.  Same applies to all the other impure preds in  
this module.

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