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

[Marc Weustink]

Mattias Gaertner wrote:
> On Tue, 17 Apr 2012 12:12:21 +0200
> Marc Weustink<marc.weustink at cuperus.nl>  wrote:
>
>> Mattias Gaertner wrote:
>>>
>>> Reimar Grabowski<reimgrab at web.de>  hat am 16. April 2012 um 16:42
>>> geschrieben:
>>>
>>>   >  Hi,
>>>   >
>>>   >  I load a TLazIntfImage from disk, manipulate it and show it on my
>>> form in a TImage. Center, Proportional and Stretch properties of the
>>> TImage are set to true.
>>>   >  Now I want to draw some overlays onto it (drawing to the canvas in
>>> the OnPaint event). Therefor I obviously need the origin and dimensions
>>> of the loaded image in 'canvas space', but I did not find a way to
>>> retrieve this information. Do I have to calculate them myself or can the
>>> TImage give me the needed information?
>>>
>>> The image is painted to the area defined by the protected method DestRect.
>>>
>>> Maybe this can be made public.
>>>
>>> At the moment you have to descend your own TImage class to access it or
>>> write a hack class (e.g. via a class helper).
>>
>> TImage is not meant to draw to. If you want to custom paint your image,
>> use a TPaintbox
>>
>> A TImage is for display only.
>
> TImage has a published OnPaint event. Painting some overlays makes
> sense. And for this you need to know where the image is on the canvas.

Who has added this ? Delphi has no OnPaint event.

Yes, if we have an event, we should provide a way to paint.
But to me this is a can of worms, since stretching is handled internally 
while the user event draws on the canvas, independent of the stretching.
If you ask me, I wouldn't have added it.

Marc