Re: Deep data API: another batch of questions.

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
>>
>>
>> _______________________________________________
>> Openexr-devel mailing list
>> [email protected]
>> https://lists.nongnu.org/mailman/listinfo/openexr-devel
>
> .

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