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Re: TortoiseIDiff - Comparison

From: Stefan Küng <tortoisesvn_at_gmail.com>
Date: 2006-09-26 17:44:19 CEST

Hans-Emil Skogh wrote:

> I have been looking a little at the image comparison problem now, and I
> have some more thoughts.
> To implement any image comparisons, one needs pixel-access to the
> images. Right now this is only available as a mem-HDC in the
> WM_PAINT-handler, and doing comparisons there is not a particularly good
> idea since a comparison may be a lengthy process.

Agreed. But you can always convert that image into a DiB and then
manipulate it from there.
As a starting point, have a look at the CDib class in

> The best way would be if we could create a way to get the raw data from
> the CPicture class. Today that's not possible as I see it. Question:

The CPicture class can be extended. You could create a DiB from a normal
DC. Here are some pointers:

> What format should we use? If we change to DevIL (ditching GDI+
> altogether), it will provide the necessary methods for raw access. Is
> that the way to go?
> Stefan, what do you say? Am I missing some obvious way to get to the
> data nicely?

After looking closer at DevIL, I found that it's actually not that small
either. It still needs a lot of other libraries (libpng, zlib, ...) to
handle other image types. I really don't like that idea.

So I'd like to keep TortoiseIDiff small and use only what's already
installed on the system.


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Received on Tue Sep 26 17:44:26 2006

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