Lottie shapes (paths) are expressed as a sequence of vertices, where
each vertex has a
- position
- in-tangent control point (relative to position)
- out-tangent control point (relative to position)
A nice property of this representation, is that interpolation can be
performed independently on each scalar component.
This seems really close to what VectorAnimator is good at - so can we
shoe-horn shapes into vectors and drop the ShapeValue KeyframeAnimator
specialization? Yes, we can!
To support the conversion, we need to abstract out two aspects of the
VectorKeyframeAnimator builder:
- parsing the encoding length of a vector-representable object
- parsing the actual encoding data of a vector-representable object
(For current/regular vector values, the encoding length is the same as
the json array length, and the encoding data is just the array of json
numbers.)
Shapes are encoded as a sequence of 6 floats per vertex, plus an
additional/trailing boolean maker for the "closed shape" property:
[v0.posX, v0.posY, v0.inX, v0.inY, v0.outX, v0.outY, ..., closed_flag ]
(thus encoding_len == 6 * vertex_count + 1)
After we're done with parsing, animation/interpolation is handled
via existing VectorKeyframeAnimator - so we can remove
KeyframeAnimator<ShapeValue>.
Converting to SkPath is pretty much the same as for the previous
representation, except the input is now flattened.
Change-Id: I822797fceae561b52b709bf258163bbcc6b565fb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/280898
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
eeaabc4ba2