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[skottie] Fix text selector sub-unit range handling

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The current logic modulates the shape generator output by its fractional
coverage, ignoring constant lo/hi contributions.

But RampUp/RampDown have non-zero hi/lo constant coverage, which needs
to be accounted for.

The correct behavior is to perform a 3-way weighted average of the
lo/hi/generator, based on their relative weights.

Change-Id: Ide0ed2ae590bbce2b56c0c65008b64632b987905
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/218962
Commit-Queue: Florin Malita <fmalita@chromium.org>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Florin Malita <fmalita@chromium.org>
Reviewed-by: Ben Wagner <bungeman@google.com>
This commit is contained in:
Florin Malita 2019-06-06 15:27:23 -04:00 committed by Skia Commit-Bot
parent 1e2d4a1159
commit 04462d12c8
1 changed files with 10 additions and 4 deletions
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14
modules/skottie/src/text/RangeSelector.cpp
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@ -288,10 +288,16 @@ void RangeSelector::modulateCoverage(TextAnimator::ModulatorBuffer& buf) const {
auto t = (i0 + 0.5f - std::get<0>(f_range)) / range_span;
if (i0 == i1) {
// The whole interval falls within a single fragment.
const auto fract_coverage = f1 - f0;
SkASSERT(fract_coverage <= 1);
generator(coverage_proc, SkTPin(t, 0.0f, 1.0f), amount * fract_coverage, buf.data() + i0);
// When the whole interval falls within a single fragment, the resulting coverage is
// a 3-way weighted average of lo/generated/hi values.
const auto lo_weight = f0 - std::floor(f0),
mi_weight = f1 - f0,
hi_weight = std::ceil(f1) - f1,
coverage = lo_weight * generator.lo +
mi_weight * generator.func(SkTPin(t, 0.0f, 1.0f)) +
hi_weight * generator.hi;
coverage_proc(amount * coverage, buf.data() + i0, 1);
} else {
// The range spans multiple fragments.