Mipmapping for canvas. Ideas and comments.

[Dmitry Kazakov]

>> Well, mipmapping  could be added  in two parts  of krita: the  first -
>> before actual merging and the second - after merging.
>>
>>
>> * The first could be done  inside KisPaintDevice class and all merging
>>  would be done with prescaled images.
>>
>> Pros:
>>      + we merge only small images, not fullsized big ones
>>      + as a consequence, filter layers and masks are applied much
>>        faster
>
> Cons: filter layers will be wrong? Color filters, no, but how do you
> even attempt to apply a custom convolution filter to an input that is
> half resolution and expect to get anything even remotely correct? (Or do
> you decide per-filter if it can be applied to downsampled input? Would
> that even be possible?)
>
> Consider especially that "filter layer" may in the future include
> debayer, which would be hideously, hideously broken by applying it to a
> downsampled input.

Well, yes. It's more theoretical and experimental issue =). Even
colors filters would suffer much because of that. In theory we could
ask a filter whether he could work with downsampled input and,
conforming to it's decision, stop or continue running merge strategy
on mipmapped tree. In theory...

Mipmapping would create too much overhead here. Nevertheless, i think
that our filter preview algo should support preview on downsampled
image. I don't know how about all filters in Photoshop, but Color
adjustment tools are cirtainly applied to downsampled image first. And
only when you press OK, it applies as usual.

-- 
Dmitry Kazakov