[fpc-pascal] Moving callbackfunctions to class

[Michael Van Canneyt]

On Fri, 31 Dec 2010, Darius Blaszyk wrote:

>
> On Dec 31, 2010, at 10:43 AM, Paul Ishenin wrote:
>
>> 31.12.2010 7:53, Darius Blaszyk wrote:
>>> I installed 2.5.1 just to test if it was possible to use static class methods or not. Apparently not so it seems. It was a good try, but it failed. Thanks anyway for the help and explanation Jonas.
>> Try {$mode delphi}.
>>
> Thanks for the tip Paul. Unfortunately it did not help. See for the results below.
>
> Delphi mode:
>
> class  -> Error: Incompatible types: got "class TfpgGLApplication.CDisplayFunc; CDecl;" expected "<procedure variable type of procedure;CDecl>"
> static -> Error: Incompatible types: got "class TfpgGLApplication.CDisplayFunc; CDecl; Static;" expected "<procedure variable type of procedure;CDecl>"
>
> ObjFPC mode:
>
> class  -> Error: Incompatible types: got "<class method type of procedure of object;CDecl>" expected "<procedure variable type of procedure;CDecl>"
> static -> Error: Incompatible types: got "<class method type of procedure of object;CDecl>" expected "<procedure variable type of procedure;CDecl>"

Even if they worked, it would do you no good: you would have no access to instance fields, 
or the VMT, since neither is passed when glut calls your callback:
- Class methods need 'self' (it will contain the VMT),
   and cannot access fields of an instance (since there is none to work with)
- Static methods do not need self, but they also cannot access fields of a class instance.
   Static methods are like regular procedures, but their name just contains a dot (.) character.

Conclusion: You can just as well use a regular procedure; the rest is a waste of your time.

Michael.