Accessing comments in a PNG file

[Tobias Reiper]

I've recently done some architectural walkthroughs (modeled in Blender and rendered with OGRE) and had trouble getting paid for them.

The first client said the check's in the mail and quit responding to any e-mails (I haven't been spamming them, they were once a week informing him that I have yet to receive payment).

For the second client I decided to get the geometry and rendering engine up and running, send it to him, and then send him the textures, along with how to install them, when I received payment.

As the second client was referred to me by the first, they were obviously in contact. I received an e-mail saying that the first client sent a copy of the texture pack used in his project and, even though I didn't feel the textures from the first project would fit the second, apparently that was enough to satisfy him.

Then when I saw The Gimp's "Save Comment" feature and figured out how to add one I got an idea. As I create each texture place a code in the comments section of each PNG, with a new series of numbers used for each project.

For example, the living room floor texture would have as a comment R21253-42652-89567, then the program would load it by texture name, check the comments, and if that string wasn't there or was incorrect it would shut the program down (no textures would allow the program to run for demonstration purposes, but incorrect textures would be proof of tampering).

The only problem with that is I have no idea how to access the comments within C++ and I haven't found much information on it.

[Raphael]

You might get away with using DSOFile to do it, that's what I use for reading and writing attributes, however, it only works on NTFS.

http://www.microsoft.com/downloads/d...displaylang=en

bit of hunting, and I found this that might help, but you would need ImgSource (not free if you don't want big red X's plastered ofver your images):
http://www.smalleranimals.com/isourc...esample_v2.htm

// open PNG
HISSRC hSrc = _ISOpenFileSource(pInputFileName);

// read it
UINT23 w, h;
HGLOBAL hRGB = _ISReadPNG(hSrc, &uOrigW, &uOrigH, 24, NULL);

// close
_ISCloseSource(hSrc);

// clean up
GlobalFree(hRGB);

// dump comment text
UINT32 uTextCount = _ISGetPNGInputTextCount();

for (UINT32 i =0; i < uTextCount; i++)
{
    HGLOBAL hText = NULL;
    HGLOBAL hKey = NULL;
    UINT32 uCompression = 0;
    _ISGetPNGInputText(i, 
                       &hKey, 
                       &hText, 
                       &uCompression);
    if (hKey)
    {
        TRACE("Read PNG comment : [%s]", (const char *)hKey);

        GlobalFree(hKey);
        if (hText)
        {
            TRACE(" %s %s", 
                  (const char *)hText, 
                  uCompression ? "(compressed)" : "");

            GlobalFree(hKey);
        }

        TRACE("\n");
    }
}

[Chrs]

You can open the picture in a Hex Editor.

EDIT: Sorry. you want a automated check. *slaps self for not reading*

Try using Regex to search for that type of string, then use a serial code type method to evaluate it? Not my sort of area, unfortunately.