I had a look at the sources and the docs, I misunderstood you post
yesterday, I thought you meant there was a way to modify the pointers of
a framebuffer. Creating a new framebuffer and insert new DeepSlices for
every batch of lines was what I was trying not to do.
But reading your messages I guess there's no other option.
On 04/21/2014 12:19 AM, Peter Hillman wrote:
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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