[Lazarus] TImage - Getting image properties in 'canvas space'

[Sven Barth]

Am 17.04.2012 22:32, schrieb Reimar Grabowski:
> On Tue, 17 Apr 2012 22:19:45 +0200
> Sven Barth<pascaldragon at googlemail.com>  wrote:
>
>> type
>>     TMyHackImage = class(TImage)
>>     public
>>       function DestRect: TRect;
>>     end;
>>
>> var
>>     MyImage: TImage;
>>     r: TRect;
>> begin
>>     // let's suppose that MyImage contains a TImage instance
>>     r := TMyHackImage(MyImage).DestRect
>> end;
> How should that work?
> What does the DestRec function look like?
> IMHO to access DestRec TMyHackImage must be derived from TCustomImage and in that case the cast won't work.

Yes, sorry. I've now tested the following example which is different 
from your original problem, but it illustrates the hacky mechanism:

=== source begin ===

program hacktest;

{$mode objfpc}

uses
   Classes;

type
   TMyStrings = class(TStringList)

   end;

var
   s: TStringList;
begin
   s := TStringList.Create;
   s.Add('Test');
   Writeln(TMyStrings(s).GetCount); // "GetCount" is protected in 
"TStringList"
end.

=== source end ===

Regards,
Sven