You will need to call setFrameBuffer before every call to
writePixels, as you need to update the frame pointers.
The pointer you pass to Slice/DeepSlice is the memory location of
pixel (0,0) in the image. This point will move in memory as you
update your memory block with different scanlines.
Your first call is probably doing the right thing. For each
subsequent call you need to set up a new FrameBuffer with
yStride*currentScanLine() subtracted from the base pointer, where
currentScanLine() is the y offset of the first scanline you are
writing.
The library will only access the memory locations it needs to for
writePixels() - there's no problem in passing an "illegal address"
as a base pointer to setFrameBuffer, as long as
(base+yStride*currentScanLine() + dataWindow.min.x*xStride) is
always a valid location when writePixels() is called.
The above is true for xSampling=1 and ySampling=1 - you may need to
adjust the logic accordingly otherwise.
On 19/04/14 21:18, Lerenard Michel
wrote:
Hi,
still trying to write deep data image, i'm
struggling a bit with FrameBuffers.
As I need to write subsampled deep images, I
cannot use Tiled images. I went for the scanline
approach. My idea was to write batches of n
scanlines, in increasing Y order.
This way I was thinking I would be able to limit the
memory footprint:
OpenEXR would not need to cache data, and I would be
able to reuse the same buffers for every batch of
lines: one buffer for Z and one for each visible
channel.
So I created a bunch of buffers, whose size was my
image width * 32. (arbitrary value). I planned to feed
these buffers to the DeepSlices I added to the
FrameBuffer.
Thing is, it appears the FrameBuffer/Slices cannot
work that way: they need to have memory allocated for
the whole image. I couldn't find any function limiting
/ defining the region I want to work on.
Here are my questions:
- Is the statement above correct ?
- Should I work differently ? I doesn't look like using
several framebuffers would help, I out of ideas at the
moment.
I can explain in more details my process if it can help.
Thanks
Michel
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