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[Impeller] Add a limit to the Gaussian blur downsampling curve #37550

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Nov 12, 2022
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[Impeller] Add a limit to the Gaussian blur downsampling curve #37550

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15 changes: 9 additions & 6 deletions impeller/display_list/display_list_unittests.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -658,6 +658,9 @@ TEST_P(DisplayListTest, CanDrawZeroLengthLine) {
TEST_P(DisplayListTest, CanDrawShadow) {
flutter::DisplayListBuilder builder;

auto content_scale = GetContentScale() * 0.8;
builder.scale(content_scale.x, content_scale.y);

constexpr size_t star_spikes = 5;
constexpr SkScalar half_spike_rotation = kPi / star_spikes;
constexpr SkScalar radius = 40;
Expand All @@ -677,24 +680,24 @@ TEST_P(DisplayListTest, CanDrawShadow) {
std::array<SkPath, 4> paths = {
SkPath{}.addRect(SkRect::MakeXYWH(0, 0, 200, 100)),
SkPath{}.addRRect(
SkRRect::MakeRectXY(SkRect::MakeXYWH(0, 0, 200, 100), 30, 30)),
SkRRect::MakeRectXY(SkRect::MakeXYWH(20, 0, 200, 100), 30, 30)),
SkPath{}.addCircle(100, 50, 50),
SkPath{}.addPoly(star.data(), star.size(), true),
};
builder.setColor(flutter::DlColor::kWhite());
builder.drawPaint();
builder.setColor(flutter::DlColor::kCyan());
builder.translate(100, 100);
builder.translate(100, 50);
for (size_t x = 0; x < paths.size(); x++) {
builder.save();
for (size_t y = 0; y < 5; y++) {
builder.drawShadow(paths[x], flutter::DlColor::kBlack(), 3 + y * 5, false,
for (size_t y = 0; y < 6; y++) {
builder.drawShadow(paths[x], flutter::DlColor::kBlack(), 3 + y * 8, false,
1);
builder.drawPath(paths[x]);
builder.translate(0, 200);
builder.translate(0, 150);
}
builder.restore();
builder.translate(300, 0);
builder.translate(250, 0);
}

ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
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7 changes: 5 additions & 2 deletions impeller/entity/contents/filters/gaussian_blur_filter_contents.cc
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Expand Up @@ -228,8 +228,11 @@ std::optional<Snapshot> DirectionalGaussianBlurFilterContents::RenderFilter(

Vector2 scale;
auto scale_curve = [](Scalar radius) {
const Scalar d = 4.0;
return std::min(1.0, d / (std::max(1.0f, radius) + d - 1.0));
constexpr Scalar decay = 4.0; // Larger is more gradual.
constexpr Scalar limit = 0.95; // The maximum percentage of the scaledown.
const Scalar curve =
std::min(1.0, decay / (std::max(1.0f, radius) + decay - 1.0));
return (curve - 1) * limit + 1;
};
{
scale.x = scale_curve(transformed_blur_radius_length);
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