Re: [Openexr-devel] OpenEXR from shared libs.

[Florian Kainz]

Hi Nicolaj,

I am not entirely sure how to interpret your example.  I assume that your
program contains a loop to read all the scan lines in a given file, but I
am not sure which of the code in your example is meant to be included in
the loop; it does make a difference.  Let's say your code is analogous to
this:

    RgbaInputFile input_file;

    Box2i dw = input_file.dataWindow();
    Rgba pixels[width];
    input_file.setFrameBuffer(pixels - dw.min.x - dw.min.y * width, 1, width);

    while (dw.min.y <= dw.max.dy)
    {
        input_file.readPixels(dw.min.y);
        dw.min.y++;
    }

If this is the case, then frame buffer address arithmetic is wrong.
No matter which scan line you are reading, you want the leftmost pixel,
t x coordinate, dw.min.x to be stored in pixels[0].  The pixels at x
coordinates dw.min.x+1, dw.min.x+2, etc. should to to pixels[1], pixels[2],
etc.  In other words, the address of pixel (x,y) is:

    pixels - dw.min.x + x

Here's the corresponding setFrameBuffer() call (see also section 2.2 of
the Reading and Writing OpenEXR Image Files document):

    input_file.setFrameBuffer (pixels - dw.min.x, 1, 0);

Hope this helps,

Florian



Nikolaj Thygesen wrote:
> Hi list,
>
>    I'm currently trying to interface to the OpenEXR library from my own 
> shared library reading scanlines one at a time. My code is heavily based 
> on the sample code on the OpenEXR home page describing the reading of an 
> RGBA file using the RgbaInputFile class + a raw copy-paste of the 
> C_IStream class using the old-skool stdio FILE *'s to access the bytes 
> of files. When compiling my program as a stand-alone program, everything 
> works fine for all sample *.exr files, but as soon as the code goes into 
> a *.so, reading crashes in the "input_file.readPixels(dw.min.y);" call 
> of the snippet below.
>
>    I should mention that I'm running FreeBSD 6.2, using gcc 4.1and 
> OpenEXR V1.2.2, which is the release currently available in the ports 
> tree. My question is: Does OpenEXR have any issues with shared libs?? Do 
> I need or should I avoid any certain compiler/linker flags??
>
>            RgbaInputFile input_file;
>
>            Box2i dw = input_file.dataWindow();
>            Rgba pixels[width];
>            input_file.setFrameBuffer(pixels - dw.min.x - dw.min.y * 
> width, 1, width);
>            input_file.readPixels(dw.min.y);
>            dw.min.y++;
>            lineno = line_number++;
>
>
>
>    br - Nikolaj Thygesen
>
>
>
>
>
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