Hi,
I realize my example was badly and incompletely reproduced. The
slightly modified version incorporating your suggested changes follows
below.
RgbaInputFile input_file;
Box2i dw = input_file.dataWindow();
Rgba pixels[width];
while (dw.min.y <= dw.max.y)
{
input_file.setFrameBuffer(pixels - dw.min.x, 1,
0);
input_file.readPixels(dw.min.y);
dw.min.y++;
}
Unfortunately even after implementing your fixes my shared lib still
crashes in readPixels() during the first scanline :o( In fact this is
what I get:
pure virtual method called
terminate called without an active exception
Abort trap: 6 (core dumped)
What you write makes much sense to me. I just can't make it fit with
the
example from section 2.5 of the OpenEXR document, in which they read a
partial image, and do this calculation for every block:
Array2D<Rgba> pixels (10, width);
while (dw.min.y <= dw.max.y)
{
file.setFrameBuffer (&pixels[0][0] - dw.min.x -
dw.min.y * width, 1, width);
file.readPixels (dw.min.y, min (dw.min.y + 9, dw.max.y));
dw.min.y += 10;
}
To me "&pixels[0][0] - dw.min.x - dw.min.y * width" looks
like you need to offset the scanline from the origo of the virtual
complete frame buffer?! I suspect that perhaps the zero byte row stride
saves us in your example - no?
Best regards - Nikolaj
Florian Kainz wrote:
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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