Re: [Openexr-devel] C API calls

[Thomas Lock]

Hi Florian

               You are correct, i fixed the calls for the dimensions and
everything works perfectly. Thank you guys.

Here's what worked perfectly

ImfInputSetFrameBuffer(fp, rgba - x1 - y1 * width, 1, width);
ImfInputReadPixels(fp, y1, y2);

Tom.


----- Original Message ----- 
From: "Florian Kainz" <address@hidden>
To: "Thomas Lock" <address@hidden>
Cc: <address@hidden>
Sent: Thursday, July 20, 2006 2:40 PM
Subject: Re: [Openexr-devel] C API calls


> *   Make sure that the file you are trying to read does actually
>      contain an image.  Start with a file that you know is good.
>      You can download a number of images from www.openexr.com.
>
> *   The ImfInputReadPixels call in your code should read
>
>          ImfInputReadPixels (fp, y1, y2);
>
> *   Your code snippets do not show how you compute width and
>      height from the data window.  Assuming that
>
>          width  = x2 - x1 + 1;
>          height = y2 - y1 + 1;
>
>      the ImfSetFrameBuffer call is incorrect; you will get a
>      crash if x1 != 0 or y1 != 0.  The call should read
>
>          ImfInputSetFrameBuffer (fp, rgba - x1 - width * y1, 1, width);
>
>      Once your file reader works, I strongly encourage you to test
>      it on all of the OpenEXR sample images that you can download
>      from www.openexr.com, in particular the DisplayWindow/t??.exr
>      files.
>
> *   The C API is only for situations where for some reason you
>      really cannot use C++.  You are probably better off using
>      the C++ API, as you did in the first version of your code.
>
>      The calls in the C API are straightforward wrappers around
>      the corresponding C++ calls.  For example,
>
>          ImfInputReadPixels (inputFile, s1, s2);
>
>      is equivalent to
>
>          inputFile.readPixels (s1, s2);
>
>      The main difference is how errors are handled: the C++ call
>      throws exceptions, while the C call returns 1 for success or
>      0 for failure.  In C++ you handle errors like this:
>
>          try
>          {
>              ...
>              inputFile.readPixels (s1, s2);
>          }
>          catch (std::exception &e)
>          {
>              std::cerr << e.what() << std::endl;
>          }
>
>      In C you do this:
>
>          if (!ImfInputReadPixels (inputFile, s1, s2))
>          {
>              fprintf (stderr, "%s\n", ImfErrorMessage());
>              return 0;
>          }
>
>
> Thomas Lock wrote:
> > I finally got it to work in debug mode, which exposed an error that
wasn't
> > coming up in release mode (not sure why). It was missing 1 library file
to
> > link to. I'm going to get reading and writing to work first in debug
mode
> > and then worry about release mode.
> > At this point i have the writing working (verified with 2 other apps),
but
> > the reading seems to have a non-fatal error (image is black but correct
> > dimensions). I don't think the buffer is getting filled properly. This
> > function is simply the opposite of what the writing function does, so
once
> > the buffer is filled and converted to my array the rest is done outside
this
> > function. I added the lines of code i believe the problem is related to,
but
> > i can't seem to find any documentation on the C API so i am guessing.
> >
> > ImfRgba *rgba;
> >
> > rgba = (ImfRgba *)malloc(width * height * sizeof(ImfRgba));
> >
> > header = ImfInputHeader(fp);
> >
> > ImfHeaderDataWindow(header,&x1,&y1,&x2,&y2);
> >
> > ImfInputSetFrameBuffer(fp, rgba , 1, width);
> >
> > ImfInputReadPixels(fp, height, 0 );
> >
> >
> >
> > ----- Original Message ----- 
> > From: "Florian Kainz" <address@hidden>
> > To: "Thomas Lock" <address@hidden>
> > Cc: <address@hidden>
> > Sent: Thursday, July 20, 2006 12:05 AM
> > Subject: Re: [Openexr-devel] C API calls
> >
> >
> >>What does "fail" mean in this case?  Does the application crash?
> >>If it does, have you tried using a debugger to get a stack trace?
> >>
> >>Does ImfOpenOutputFile return a null pointer?  If you do get a null
> >>pointer, have you tried calling ImfErrorMessage() to find get some
> >>diagnostic output?  Your example contains no error checking code.
> >>Unlike the C++ interface, the C interface does not throw exceptions;
> >>you must explicitly check the return values of the functions you call.
> >>
> >>Thomas Lock wrote:
> >>>Hi Drew
> >>>
> >>>             I completely rewrote my code to meet the C API calls. This
> > time
> >>>i get zero warnings or errors but the app specifically fails on this
> > call
> >>>"file = ImfOpenOutputFile(filenames, header, IMF_WRITE_RGBA );". I
tried
> > a
> >>>variety of filename options and nothing seems to work. I can't verify
if
> > my
> >>>remaining code works, but i believe it is correct.
> >>>
> >>>extern "C" void WINAPI writeOpenEXR (char *filename, int width, int
> > height,
> >>>float* Bits128)
> >>>{
> >>>        int LineWidth=width*4;
> >>>        float fwidth;
> >>>        const char fileName[] = "c:\foo2.exr";
> >>>        const char *filenames = "c:\foo2.exr";
> >>>
> >>>        ImfOutputFile *file;
> >>>        ImfRgba *base;
> >>>        base = (ImfRgba *)malloc(width * height * sizeof(ImfRgba));
> >>>        fwidth = (float)width;
> >>>        ImfHeader *header;
> >>>        header = ImfNewHeader();
> >>>        ImfHeaderSetDisplayWindow(header, 0, 0, width - 1, height - 1);
> >>>        ImfHeaderSetDataWindow(header, 0, 0, width - 1, height - 1);
> >>>        ImfHeaderSetScreenWindowWidth(header, fwidth);
> >>>        file = ImfOpenOutputFile(filenames, header, IMF_WRITE_RGBA );
> >>>
> >>>        ImfDeleteHeader(header);
> >>>
> >>>        for(int h=0;h<height;h++)for(int b=0;b<width;b++)
> >>>       {
> >>>            ImfHalf half;
> >>>
> >>>            int i=h*LineWidth+(b<<2);
> >>>            int j=h*LineWidth+b;
> >>>
> >>>            ImfFloatToHalf(Bits128[i], &half);
> >>>            base[j].b = half;
> >>>
> >>>            ImfFloatToHalf(Bits128[i + 1], &half);
> >>>            base[j].g = half;
> >>>
> >>>            ImfFloatToHalf(Bits128[i + 2], &half);
> >>>            base[j].r = half;
> >>>
> >>>            ImfFloatToHalf(Bits128[i + 3], &half);
> >>>            base[j].a = half;
> >>>        }
> >>>
> >>>        ImfOutputSetFrameBuffer( file, base, 1, width );
> >>>        ImfOutputWritePixels(file, height );
> >>>        ImfCloseOutputFile(file);
> >>>
> >>>        free(base);
> >>>}
> >>>
> >>>
> >>>
> >>>
> >>>_______________________________________________
> >>>Openexr-devel mailing list
> >>>address@hidden
> >>>http://lists.nongnu.org/mailman/listinfo/openexr-devel
> >>>
> >>>
> >
> >
> >
> >
>