SkWuffsCodec: Use drawing to do color correction and scaling
Bug: skia:8235 (Wuffs)
Bug: skia:8751 (Color correction)
Bug: skia:8762 (565)
This was brought up in https://skia-review.googlesource.com/c/skia/+/171645/1/src/codec/SkWuffsCodec.cpp#499
Remove the SkSwizzler and code that supports it (e.g.
SkWuffsSpySampler). In its place, use an SkDraw and draw from Wuffs'
working buffer into the output pixel memory. This trivially allows
support for 565 and f16, while removing the blend function that was
8888 specific. The draw operation also takes care of color correction
and allows arbitrary downscaling.
Add the intermediate subclass SkScalingCodec, to share methods between
SkWebpCodec and SkWuffsCodec.
Allowing arbitrary scaling from an SkCodec subclass is a bit of a break
from an original goal of SkCodec, which was to only do what the
underlying format supports naturally. Otherwise a client could just use
Skia to do effectively the same thing in a layer above SkCodec. (e.g.
jpegs can be downscaled by throwing away information during decode,
which libjpeg(-turbo) will do as requested. But gifs don't scale down
naturally in the same way, so SkGifCodec did not support downscaling
except when used with SkAndroidCodec.) But SkCodec has already deviated
from this goals in two ways. With SkAndroidCodec, sampling is done
inside SkGifCodec (and others) in order to save on memory allocation (we
can sample on a single line without allocating memory for the full size
image at its original size). (Note that this memory is not saved anyway
in SkWuffsCodec, because wuffs has its own image buffer.) The second
deviation is color correction, which could also be done in a layer
outside SkCodec. Since SkCodec is already doing this extra work,
simplify it.
Change-Id: If9a1698e0c353f60250aef5b6229855e6538a42d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/194186
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Nigel Tao <nigeltao@google.com>
5 files changed