Re: Deep data API: another batch of questions.

The docs hold a fully fleshed out version of this approach for flat images
that serve as an excellent example.

Piotr



On 21 April 2014 09:02, Lerenard Michel <[email protected]> wrote:

> Thanks for your answer. I didn't thought I could pass an "illegal" pointer
> to the function, i'll try this method instead.
>
>
> 2014-04-21 0:19 GMT+02:00 Peter Hillman <[email protected]>:
>
>  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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>>
>>
>>
>
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