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/*
* Copyright (C) 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "StretchEffect.h"
#include <SkImageFilter.h>
#include <SkRefCnt.h>
#include <SkRuntimeEffect.h>
#include <SkString.h>
#include <SkSurface.h>
#include <include/effects/SkImageFilters.h>
#include <memory>
namespace android::uirenderer {
static const SkString stretchShader = SkString(R"(
uniform shader uContentTexture;
// multiplier to apply to scale effect
uniform float uMaxStretchIntensity;
// Maximum percentage to stretch beyond bounds of target
uniform float uStretchAffectedDist;
// Distance stretched as a function of the normalized overscroll times
// scale intensity
uniform float uDistanceStretchedX;
uniform float uDistanceStretchedY;
uniform float uDistDiffX;
// Difference between the peak stretch amount and overscroll amount normalized
uniform float uDistDiffY;
// Horizontal offset represented as a ratio of pixels divided by the target width
uniform float uScrollX;
// Vertical offset represented as a ratio of pixels divided by the target height
uniform float uScrollY;
// Normalized overscroll amount in the horizontal direction
uniform float uOverscrollX;
// Normalized overscroll amount in the vertical direction
uniform float uOverscrollY;
uniform float viewportWidth; // target height in pixels
uniform float viewportHeight; // target width in pixels
void computeOverscrollStart(
out float outPos,
float inPos,
float overscroll,
float uStretchAffectedDist,
float distanceStretched
) {
float offsetPos = uStretchAffectedDist - inPos;
float posBasedVariation = smoothstep(0., uStretchAffectedDist, offsetPos);
float stretchIntensity = overscroll * posBasedVariation;
outPos = distanceStretched - (offsetPos / (1. + stretchIntensity));
}
void computeOverscrollEnd(
out float outPos,
float inPos,
float overscroll,
float reverseStretchDist,
float uStretchAffectedDist,
float distanceStretched
) {
float offsetPos = inPos - reverseStretchDist;
float posBasedVariation = (smoothstep(0., uStretchAffectedDist, offsetPos));
float stretchIntensity = (-overscroll) * posBasedVariation;
outPos = 1 - (distanceStretched - (offsetPos / (1. + stretchIntensity)));
}
void computeOverscroll(
out float outPos,
float inPos,
float overscroll,
float uStretchAffectedDist,
float distanceStretched,
float distanceDiff
) {
if (overscroll > 0) {
if (inPos <= uStretchAffectedDist) {
computeOverscrollStart(
outPos,
inPos,
overscroll,
uStretchAffectedDist,
distanceStretched
);
} else if (inPos >= distanceStretched) {
outPos = distanceDiff + inPos;
}
}
if (overscroll < 0) {
float stretchAffectedDist = 1. - uStretchAffectedDist;
if (inPos >= stretchAffectedDist) {
computeOverscrollEnd(
outPos,
inPos,
overscroll,
stretchAffectedDist,
uStretchAffectedDist,
distanceStretched
);
} else if (inPos < stretchAffectedDist) {
outPos = -distanceDiff + inPos;
}
}
}
vec4 main(vec2 coord) {
// Normalize SKSL pixel coordinate into a unit vector
float inU = coord.x / viewportWidth;
float inV = coord.y / viewportHeight;
float outU;
float outV;
float stretchIntensity;
// Add the normalized scroll position within scrolling list
inU += uScrollX;
inV += uScrollY;
outU = inU;
outV = inV;
computeOverscroll(
outU,
inU,
uOverscrollX,
uStretchAffectedDist,
uDistanceStretchedX,
uDistDiffX
);
computeOverscroll(
outV,
inV,
uOverscrollY,
uStretchAffectedDist,
uDistanceStretchedY,
uDistDiffY
);
coord.x = outU * viewportWidth;
coord.y = outV * viewportHeight;
return sample(uContentTexture, coord);
})");
static const float ZERO = 0.f;
sk_sp<SkImageFilter> StretchEffect::getImageFilter(const sk_sp<SkImage>& snapshotImage) const {
if (isEmpty()) {
return nullptr;
}
if (mStretchFilter != nullptr) {
return mStretchFilter;
}
float distanceNotStretchedX = maxStretchAmount / stretchArea.width();
float distanceNotStretchedY = maxStretchAmount / stretchArea.height();
float normOverScrollDistX = mStretchDirection.x();
float normOverScrollDistY = mStretchDirection.y();
float distanceStretchedX = maxStretchAmount / (1 + abs(normOverScrollDistX));
float distanceStretchedY = maxStretchAmount / (1 + abs(normOverScrollDistY));
float diffX = distanceStretchedX - distanceNotStretchedX;
float diffY = distanceStretchedY - distanceNotStretchedY;
float viewportWidth = stretchArea.width();
float viewportHeight = stretchArea.height();
if (mBuilder == nullptr) {
mBuilder = std::make_unique<SkRuntimeShaderBuilder>(getStretchEffect());
}
mBuilder->child("uContentTexture") = snapshotImage->makeShader(
SkTileMode::kClamp, SkTileMode::kClamp, SkSamplingOptions(SkFilterMode::kLinear));
mBuilder->uniform("uStretchAffectedDist").set(&maxStretchAmount, 1);
mBuilder->uniform("uDistanceStretchedX").set(&distanceStretchedX, 1);
mBuilder->uniform("uDistanceStretchedY").set(&distanceStretchedY, 1);
mBuilder->uniform("uDistDiffX").set(&diffX, 1);
mBuilder->uniform("uDistDiffY").set(&diffY, 1);
mBuilder->uniform("uOverscrollX").set(&normOverScrollDistX, 1);
mBuilder->uniform("uOverscrollY").set(&normOverScrollDistY, 1);
mBuilder->uniform("uScrollX").set(&ZERO, 1);
mBuilder->uniform("uScrollY").set(&ZERO, 1);
mBuilder->uniform("viewportWidth").set(&viewportWidth, 1);
mBuilder->uniform("viewportHeight").set(&viewportHeight, 1);
mStretchFilter = SkImageFilters::Shader(mBuilder->makeShader(nullptr, false),
SkRect{0, 0, viewportWidth, viewportHeight});
return mStretchFilter;
}
sk_sp<SkRuntimeEffect> StretchEffect::getStretchEffect() {
const static SkRuntimeEffect::Result instance = SkRuntimeEffect::Make(stretchShader);
return instance.effect;
}
} // namespace android::uirenderer
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