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Date Posted: 17:35:06 10/31/01 Wed
Author: Michel
Subject: Re: Invalid Pointer Operation
In reply to: Tim Griffin 's message, "Re: Invalid Pointer Operation" on 14:07:36 10/29/01 Mon

Hi Tim,

The code I am currently working on is a thumbnail viewer. Also planned is an easy to use thumbnail generator but I have started that, and it will be included in version 2.

You could modify your thumbnail code posted to avoid using a TImageScrollBox, by using TDibGraphic objects directory and the TResizeTransform. See the NewDibGraphic function in the online help, which returns a TDibGraphic class for a specific file format.

Best regards,


>Thanks Michel!
>I had AGraphic defined as TDibGraphic instead of
>Please forward to me your thumbnails code also as the
>code below is simply doing a thumbnail and I would
>like very much to see your example.
>Thanks again!
>>Hi Tim,
>>Just from the code it is hard to tell. The AGraphic,
>>is it really a TJpegGraphic? Try using (AGraphic as
>>TJpegGraphic) rather than TJpegGraphic(AGraphic) just
>>as a safeguard.
>>Also, try tracing in your unit finalization sections
>>with the debugger. Are you global objects being
>>properly freed?
>>Best regards,
>>>The following Delphi 5 code generates a 1/2 size JPG
>>>and produces an "Invalid Pointer Operation" upon
>>>closing the program. This happens with our without
>>>Delphi running. The problem does not occur if this
>>>code is skipped.
>>>AGraphic is defined globally and Transform is defined
>>>locally but the problem also occured when AGraphic
>>>also defined locally.
>>>Also, ImageScrollBox1 is enabled but not visable.
>>>Please advise.
>>>Thanks much!
>>> Transform := TResizeTransform.Create;
>>> ImageScrollBox1.LoadFromFile(InFileName,0);
>>> AGraphic.assign(ImageScrollBox1.Graphic);
>>> TJpegGraphic(AGraphic).SaveQuality :=
>>> h := ImageScrollBox1.Graphic.Height;
>>> w := ImageScrollBox1.Graphic.Width;
>>> ratio := 0.5;
>>> try
>>> Transform.Width := trunc(w * ratio);
>>> Transform.Height := trunc(h * ratio);
>>> Transform.ApplyOnDest(AGraphic,
>>> ImageScrollBox1.SaveToFile(OutFileName);
>>> finally
>>> Transform.Free;
>>> end;

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