[Impeller] mask blurs on ColorSourceContents stretches the contents #144836
Description
As part of implementing mask blurs on textures we had to make sure we are sampling outside of texture to give coverage to the blur radius. It was discovered that that is the same sort of math we should be doing in non-solid colors as well. Not doing that is causing slight stretching of gradients.
See also:
flutter/engine#51183 (comment)
reproduction
TEST_P(AiksTest, MaskBlurDoesntStretchContents) {
Scalar sigma = 70;
auto callback = [&](AiksContext& renderer) -> std::optional<Picture> {
if (AiksTest::ImGuiBegin("Controls", nullptr,
ImGuiWindowFlags_AlwaysAutoResize)) {
ImGui::SliderFloat("Sigma", &sigma, 0, 500);
ImGui::End();
}
Canvas canvas;
canvas.Scale(GetContentScale());
canvas.DrawPaint({.color = Color(0.1, 0.1, 0.1, 1.0)});
std::shared_ptr<Texture> boston = CreateTextureForFixture("boston.jpg");
ColorSource image_source = ColorSource::MakeImage(
boston, Entity::TileMode::kRepeat, Entity::TileMode::kRepeat, {}, {});
canvas.Transform(Matrix::MakeTranslation({100, 100, 0}) *
Matrix::MakeScale({0.5, 0.5, 1.0}));
Paint paint = {
.color_source = image_source,
.mask_blur_descriptor =
Paint::MaskBlurDescriptor{
.style = FilterContents::BlurStyle::kNormal,
.sigma = Sigma(sigma),
},
};
canvas.DrawRect(
Rect::MakeXYWH(0, 0, boston->GetSize().width, boston->GetSize().height),
paint);
return canvas.EndRecordingAsPicture();
};
ASSERT_TRUE(OpenPlaygroundHere(callback));
}