The SkM44::RectToRect function matches the semantics of
SkMatrix::RectToRect(kFill_ScaleToFit). No other ScaleToFit variants are
ported over to SkM44.
skottie uses some instances of kCenter_ScaleToFit so that functionality
may need to be added in the future (in SkM44 or in skottie). There are
no current usages of the kStart and kEnd_ScaleToFit semantics.
The SkM44::mapRect() function is implemented to correspond to the
SkMatrix::mapRect() that returns the mapped rect (instead of modifying a
pointer) and always has ApplyPerspectiveClip::kYes. This was chosen to
keep its behavior simple and because perspective clipping is almost
always the right thing to do. In the new implementation there is no
longer a performance cliff to worry about (see below). For the timebeing
mapRect is hidden behind SkMatrixPriv::MapRect().
Performance:
I added benchmarks for mapRect() on SkM44 and SkMatrix that use the same
matrices to get a fair comparison on their different specializations.
SkMatrix has a very efficient mapRect when it's scale+translate or
simpler, then another impl. for affine matrices, and then falls back to
SkPath clipping when there's perspective. On the other hand, SkM44 only
has 2 modes: affine and perspective.
On my desktop, with a Ryzen 9 3900X, here are the times for 100,000 calls
to mapRect for different types of matrices:
SkMatrix SkM44
scale+translate 0.35 ms 0.42 ms
rotate 1.70 ms 0.42 ms
perspective 63.90 ms 0.66 ms
clipped-perspective 138.0 ms 0.96 ms
To summarize, the SkM44::mapRect is almost as fast as the s+t specialization
in SkMatrix, but for all non-perspective matrices. For perspective matrices
it's only 2x slower than that specialization when no vertices are clipped,
and still almost 2x faster than the affine specialization when vertices are
clipped (and 100x faster than falling back to SkPath).
Given that, there's the open question of whether or not keeping an affine
specialization is worth it for SkM44's code size.
Bug: skia:11720
Change-Id: I6771956729ed64f3b287a9de503513375c9f42a0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/402957
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
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