The Chromium Chronicle #33: Views AnimationBuilder

Episode 33: by Allen Bauer in Mountain View, USA (April, 2023)
Previous episodes

Using layer based animations in Views can improve performance and reduce jankiness, but they’re rather difficult to set up. The AnimationBuilder classes can vastly reduce complexity and improve readability for layer animations.

Suppose you needed to animate a continuous cross-fade between the following two views, such as in the following image.

Here is an example of how this could be done using the layer animation APIs directly.

auto primary_title_sequence = std::make_unique<LayerAnimationSequence>();
auto working_sequence = std::make_unique<LayerAnimationSequence>();
primary_title_sequence->set_is_repeating(true);
working_sequence->set_is_repeating(true);

primary_title_sequence->AddElement(CreatePauseElement(OPACITY, base::Seconds(2)));
primary_title_sequence->AddElement(CreateOpacityElement(0.0f, base::Seconds(1)));
primary_title_sequence->AddElement(CreatePauseElement(OPACITY, base::Seconds(2)));
primary_title_sequence->AddElement(CreateOpacityElement(1.0f, base::Seconds(1)));

working_sequence->AddElement(CreatePauseElement(OPACITY, base::Seconds(2)));
working_sequence->AddElement(CreateOpacityElement(1.0f, base::Seconds(1)));
working_sequence->AddElement(CreatePauseElement(OPACITY, base::Seconds(2)));
working_sequence->AddElement(CreateOpacityElement(0.0f, base::Seconds(1)));

primary_title_->layer()->GetAnimator()->StartAnimation(primary_title_sequence.release());
working_->layer()->GetAnimator()->StartAnimation(working_sequence.release());

The following shows how to create the same effect using AnimationBuilder. The animation will start upon exiting the scope.

AnimationBuilder()
.Repeatedly()
.Offset(base::Seconds(2))
.SetDuration(base::Seconds(1))
.SetOpacity(primary_title_, 0.0f)
.SetOpacity(working_, 1.0f)
.Offset(base::Seconds(2))
.SetDuration(base::Seconds(1))
.SetOpacity(primary_title_, 1.0f)
.SetOpacity(working_, 0.0f);

Which code would you rather write or read? More importantly, AnimationBuilder adds no extra overhead to the animation as it is intended to simplify the creation of layer-based animations. Give it a try the next time you need to animate something.

For additional help, email chromium-dev@chromium.org.

• AnimationBuilder documentation
• Learning about Chromium UI