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From: Manuel Collado <m.collado@domain.ivalid>
Newsgroups: comp.lang.ada
Subject: Re: How to get the mouse position with JEWL?
Date: Thu, 21 Oct 2010 00:22:56 +0200
Organization: Universitat de Valencia
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Date: 2010-10-21T00:22:56+02:00
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El 20/10/2010 19:20, tolkamp escribi�:
> On 20 okt, 13:42, Manuel Collado<m.coll...@domain.invalid>  wrote:
>> El 20/10/2010 11:04, tolkamp escribi�:
>>
>>> I use JEWL in several of my applications.
>>> Now I try to get the mouse position within a JEWL canvas by using the
>>> function "End_Point(Canavas)".
>>> The resulting mouse position (x,y) is always zero. What is going wrong?
>>
>> Please try:
>>
>>    point := Start_Point( canvas );
>>
>> It works for me.
>>
>
> Also when I try:
>   point := Start_Point( canvas );
> the x and y position remains zero.
>
> Here is the code:
>
> task body Task_2Hz is
> My_Frame  : Frame_Type;
> My_Canvas : Canvas_Type;
> My_Mouse_Position : Point_Type;
> begin
>      accept Start do
>         My_Frame   := Frame (1200, 500, "", 0);
>         My_Canvas  := Canvas (Frame, (850,10),      300, 300);
> loop
>         My_Mouse_Position := Start_Point(My_Canvas);
>         Put("Mouse-x = "); Int_Io.Put(My_Mouse_Position.x); New_Line;
>         Put("Mouse-y = "); Int_Io.Put(My_Mouse_Position.y); New_Line;
>     delay 0.5;
> end loop;
> end Task_2Hz;

IIRC, you must wait for a mouse event before reading the coordinates. 
Here is a code fragment of a real program that uses a canvas. You may 
figure how to adapt it to your needs:

    function Get_Point return Point_Type is
       Here: Point_Type;
    begin
       loop
          case Next_Command is
             when Cmd_Mouse =>
                exit;
             when Cmd_Quit =>
                raise Program_Aborted;
             when others =>
                null;
          end case;
       end loop;
       Here := Start_Point( Main_Canvas );
       return Logical( Here );
    end Get_Point;

Hope it helps.
-- 
Manuel Collado - http://lml.ls.fi.upm.es/~mcollado