MM Introduce a Kotlin type-safe builder for DirectionalMotionSpec (ad6bfdf4) · Commits · e / os / android_frameworks_libs_systemui

mechanics/src/com/android/mechanics/spec/DirectionalMotionSpecBuilder.kt

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		/*
		* Copyright (C) 2025 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.
		*/

		package com.android.mechanics.spec

		import com.android.mechanics.spring.SpringParameters

		/**
		* Builds a [DirectionalMotionSpec] by defining a sequence of ([Breakpoint], [Mapping]) pairs.
		*
		* This function simplifies the creation of complex motion specifications. It allows you to define a
		* series of motion segments, each with its own behavior, separated by breakpoints. The breakpoints
		* and their corresponding segments will always be ordered from min to max value, regardless of how
		* the `DirectionalMotionSpec` is applied.
		*
		* Example Usage:
		* ```kotlin
		* val motionSpec = buildDirectionalMotionSpec(
		* defaultSpring = materialSpatial,
		*
		* // Start as a constant transition, always 0.
		* initialMapping = Mapping.Zero
		* ) {
		* // At breakpoint 10: Linear transition from 0 to 50.
		* target(breakpoint = 10f, from = 0f, to = 50f)
		*
		* // At breakpoint 20: Jump +5, and constant value 55.
		* constantValueFromCurrent(breakpoint = 20f, delta = 5f)
		*
		* // At breakpoint 30: Jump to 40. Linear mapping using: progress_since_breakpoint * fraction.
		* fractionalInput(breakpoint = 30f, from = 40f, fraction = 2f)
		* }
		* ```
		*
		* @param defaultSpring The default [SpringParameters] to use for all breakpoints.
		* @param initialMapping The initial [Mapping] for the first segment (defaults to
		* [Mapping.Identity]).
		* @param init A lambda function that configures the [DirectionalMotionSpecBuilder]. The lambda
		* should return a [CanBeLastSegment] to indicate the end of the spec.
		* @return The constructed [DirectionalMotionSpec].
		*/
		fun buildDirectionalMotionSpec(
		defaultSpring: SpringParameters,
		initialMapping: Mapping = Mapping.Identity,
		init: DirectionalMotionSpecBuilder.() -> CanBeLastSegment,
		): DirectionalMotionSpec {
		return DirectionalMotionSpecBuilderImpl(defaultSpring)
		.also { it.mappings += initialMapping }
		.also { it.init() }
		.build()
		}

		/**
		* Builds a simple [DirectionalMotionSpec] with a single segment.
		*
		* @param mapping The [Mapping] to apply to the segment. Defaults to [Mapping.Identity].
		* @return A new [DirectionalMotionSpec] instance configured with the provided parameters.
		*/
		fun buildDirectionalMotionSpec(mapping: Mapping = Mapping.Identity): DirectionalMotionSpec {
		return DirectionalMotionSpec(listOf(Breakpoint.minLimit, Breakpoint.maxLimit), listOf(mapping))
		}

		/**
		* Defines the contract for building a [DirectionalMotionSpec].
		*
		* Provides methods to define breakpoints and mappings for the motion specification.
		*/
		interface DirectionalMotionSpecBuilder {
		/** The default [SpringParameters] used for breakpoints. */
		val defaultSpring: SpringParameters

		/**
		* Ends the current segment at the [breakpoint] position and defines the next segment to
		* linearly interpolate from a starting value ([from]) to the desired target value ([to]).
		*
		* Note: This segment cannot be used as the last segment in the specification, as it requires a
		* subsequent breakpoint to define the target value.
		*
		* @param breakpoint The breakpoint defining the end of the current segment and the start of the
		* next.
		* @param from The output value at the previous breakpoint, explicitly setting the starting
		* point for the linear mapping.
		* @param to The desired output value at the new breakpoint.
		* @param spring The [SpringParameters] for the transition to this breakpoint. Defaults to
		* [defaultSpring].
		* @param guarantee The animation guarantee for this transition. Defaults to [Guarantee.None].
		* @param key A unique [BreakpointKey] for this breakpoint. Defaults to a newly generated key.
		*/
		fun target(
		breakpoint: Float,
		from: Float,
		to: Float,
		spring: SpringParameters = defaultSpring,
		guarantee: Guarantee = Guarantee.None,
		key: BreakpointKey = BreakpointKey(),
		)

		/**
		* Ends the current segment at the [breakpoint] position and defines the next segment to
		* linearly interpolate from the current output value (optionally with an offset of [delta]) to
		* the desired target value ([to]).
		*
		* Note: This segment cannot be used as the last segment in the specification, as it requires a
		* subsequent breakpoint to define the target value.
		*
		* @param breakpoint The breakpoint defining the end of the current segment and the start of the
		* next.
		* @param to The desired output value at the new breakpoint.
		* @param delta An optional offset to apply to the calculated starting value. Defaults to 0f.
		* @param spring The [SpringParameters] for the transition to this breakpoint. Defaults to
		* [defaultSpring].
		* @param guarantee The animation guarantee for this transition. Defaults to [Guarantee.None].
		* @param key A unique [BreakpointKey] for this breakpoint. Defaults to a newly generated key.
		*/
		fun targetFromCurrent(
		breakpoint: Float,
		to: Float,
		delta: Float = 0f,
		spring: SpringParameters = defaultSpring,
		guarantee: Guarantee = Guarantee.None,
		key: BreakpointKey = BreakpointKey(),
		)

		/**
		* Ends the current segment at the [breakpoint] position and defines the next segment to
		* linearly interpolate from a starting value ([from]) and then continue with a fractional input
		* ([fraction]).
		*
		* Note: This segment can be used as the last segment in the specification.
		*
		* @param breakpoint The breakpoint defining the end of the current segment and the start of the
		* next.
		* @param from The output value at the previous breakpoint, explicitly setting the starting
		* point for the linear mapping.
		* @param fraction The fractional multiplier applied to the input difference between
		* breakpoints.
		* @param spring The [SpringParameters] for the transition to this breakpoint. Defaults to
		* [defaultSpring].
		* @param guarantee The animation guarantee for this transition. Defaults to [Guarantee.None].
		* @param key A unique [BreakpointKey] for this breakpoint. Defaults to a newly generated key.
		*/
		fun fractionalInput(
		breakpoint: Float,
		from: Float,
		fraction: Float,
		spring: SpringParameters = defaultSpring,
		guarantee: Guarantee = Guarantee.None,
		key: BreakpointKey = BreakpointKey(),
		): CanBeLastSegment

		/**
		* Ends the current segment at the [breakpoint] position and defines the next segment to
		* linearly interpolate from the current output value (optionally with an offset of [delta]) and
		* then continue with a fractional input ([fraction]).
		*
		* Note: This segment can be used as the last segment in the specification.
		*
		* @param breakpoint The breakpoint defining the end of the current segment and the start of the
		* next.
		* @param fraction The fractional multiplier applied to the input difference between
		* breakpoints.
		* @param delta An optional offset to apply to the calculated starting value. Defaults to 0f.
		* @param spring The [SpringParameters] for the transition to this breakpoint. Defaults to
		* [defaultSpring].
		* @param guarantee The animation guarantee for this transition. Defaults to [Guarantee.None].
		* @param key A unique [BreakpointKey] for this breakpoint. Defaults to a newly generated key.
		*/
		fun fractionalInputFromCurrent(
		breakpoint: Float,
		fraction: Float,
		delta: Float = 0f,
		spring: SpringParameters = defaultSpring,
		guarantee: Guarantee = Guarantee.None,
		key: BreakpointKey = BreakpointKey(),
		): CanBeLastSegment

		/**
		* Ends the current segment at the [breakpoint] position and defines the next segment to output
		* a constant value ([value]).
		*
		* Note: This segment can be used as the last segment in the specification.
		*
		* @param breakpoint The breakpoint defining the end of the current segment and the start of the
		* next.
		* @param value The constant output value for this segment.
		* @param spring The [SpringParameters] for the transition to this breakpoint. Defaults to
		* [defaultSpring].
		* @param guarantee The animation guarantee for this transition. Defaults to [Guarantee.None].
		* @param key A unique [BreakpointKey] for this breakpoint. Defaults to a newly generated key.
		*/
		fun constantValue(
		breakpoint: Float,
		value: Float,
		spring: SpringParameters = defaultSpring,
		guarantee: Guarantee = Guarantee.None,
		key: BreakpointKey = BreakpointKey(),
		): CanBeLastSegment

		/**
		* Ends the current segment at the [breakpoint] position and defines the next segment to output
		* a constant value derived from the current output value (optionally with an offset of
		* [delta]).
		*
		* Note: This segment can be used as the last segment in the specification.
		*
		* @param breakpoint The breakpoint defining the end of the current segment and the start of the
		* next.
		* @param delta An optional offset to apply to the mapped value to determine the constant value.
		* Defaults to 0f.
		* @param spring The [SpringParameters] for the transition to this breakpoint. Defaults to
		* [defaultSpring].
		* @param guarantee The animation guarantee for this transition. Defaults to [Guarantee.None].
		* @param key A unique [BreakpointKey] for this breakpoint. Defaults to a newly generated key.
		*/
		fun constantValueFromCurrent(
		breakpoint: Float,
		delta: Float = 0f,
		spring: SpringParameters = defaultSpring,
		guarantee: Guarantee = Guarantee.None,
		key: BreakpointKey = BreakpointKey(),
		): CanBeLastSegment

		/**
		* Ends the current segment at the [breakpoint] position and defines the next segment using the
		* provided [mapping].
		*
		* Note: This segment can be used as the last segment in the specification.
		*
		* @param breakpoint The breakpoint defining the end of the current segment and the start of the
		* next.
		* @param spring The [SpringParameters] for the transition to this breakpoint. Defaults to
		* [defaultSpring].
		* @param guarantee The animation guarantee for this transition. Defaults to [Guarantee.None].
		* @param key A unique [BreakpointKey] for this breakpoint. Defaults to a newly generated key.
		* @param mapping The custom [Mapping] to use.
		*/
		fun mapping(
		breakpoint: Float,
		spring: SpringParameters = defaultSpring,
		guarantee: Guarantee = Guarantee.None,
		key: BreakpointKey = BreakpointKey(),
		mapping: Mapping,
		): CanBeLastSegment
		}

		/** Marker interface to indicate that a segment can be the last one in a [DirectionalMotionSpec]. */
		sealed interface CanBeLastSegment

		private data object CanBeLastSegmentImpl : CanBeLastSegment

		private class DirectionalMotionSpecBuilderImpl(override val defaultSpring: SpringParameters) :
		DirectionalMotionSpecBuilder {
		private val breakpoints = mutableListOf(Breakpoint.minLimit)
		val mappings = mutableListOf<Mapping>()

		private var sourceValue: Float = Float.NaN
		private var targetValue: Float = Float.NaN
		private var fractionalMapping: Float = Float.NaN
		private var breakpointPosition: Float = Float.NaN
		private var breakpointKey: BreakpointKey? = null

		override fun target(
		breakpoint: Float,
		from: Float,
		to: Float,
		spring: SpringParameters,
		guarantee: Guarantee,
		key: BreakpointKey,
		) {
		toBreakpointImpl(breakpoint, key)
		jumpToImpl(from, spring, guarantee)
		continueWithTargetValueImpl(to)
		}

		override fun targetFromCurrent(
		breakpoint: Float,
		to: Float,
		delta: Float,
		spring: SpringParameters,
		guarantee: Guarantee,
		key: BreakpointKey,
		) {
		toBreakpointImpl(breakpoint, key)
		jumpByImpl(delta, spring, guarantee)
		continueWithTargetValueImpl(to)
		}

		override fun fractionalInput(
		breakpoint: Float,
		from: Float,
		fraction: Float,
		spring: SpringParameters,
		guarantee: Guarantee,
		key: BreakpointKey,
		): CanBeLastSegment {
		toBreakpointImpl(breakpoint, key)
		jumpToImpl(from, spring, guarantee)
		continueWithFractionalInputImpl(fraction)
		return CanBeLastSegmentImpl
		}

		override fun fractionalInputFromCurrent(
		breakpoint: Float,
		fraction: Float,
		delta: Float,
		spring: SpringParameters,
		guarantee: Guarantee,
		key: BreakpointKey,
		): CanBeLastSegment {
		toBreakpointImpl(breakpoint, key)
		jumpByImpl(delta, spring, guarantee)
		continueWithFractionalInputImpl(fraction)
		return CanBeLastSegmentImpl
		}

		override fun constantValue(
		breakpoint: Float,
		value: Float,
		spring: SpringParameters,
		guarantee: Guarantee,
		key: BreakpointKey,
		): CanBeLastSegment {
		toBreakpointImpl(breakpoint, key)
		jumpToImpl(value, spring, guarantee)
		continueWithConstantValueImpl()
		return CanBeLastSegmentImpl
		}

		override fun constantValueFromCurrent(
		breakpoint: Float,
		delta: Float,
		spring: SpringParameters,
		guarantee: Guarantee,
		key: BreakpointKey,
		): CanBeLastSegment {
		toBreakpointImpl(breakpoint, key)
		jumpByImpl(delta, spring, guarantee)
		continueWithConstantValueImpl()
		return CanBeLastSegmentImpl
		}

		override fun mapping(
		breakpoint: Float,
		spring: SpringParameters,
		guarantee: Guarantee,
		key: BreakpointKey,
		mapping: Mapping,
		): CanBeLastSegment {
		toBreakpointImpl(breakpoint, key)
		continueWithImpl(mapping, spring, guarantee)
		return CanBeLastSegmentImpl
		}

		fun build(): DirectionalMotionSpec {
		completeImpl()
		return DirectionalMotionSpec(breakpoints.toList(), mappings.toList())
		}

		private fun continueWithTargetValueImpl(target: Float) {
		check(sourceValue.isFinite())

		targetValue = target
		}

		private fun continueWithFractionalInputImpl(fraction: Float) {
		check(sourceValue.isFinite())

		fractionalMapping = fraction
		}

		private fun continueWithConstantValueImpl() {
		check(sourceValue.isFinite())

		mappings.add(Mapping.Fixed(sourceValue))
		sourceValue = Float.NaN
		}

		private fun jumpToImpl(value: Float, spring: SpringParameters, guarantee: Guarantee) {
		check(sourceValue.isNaN())

		doAddBreakpointImpl(spring, guarantee)
		sourceValue = value
		}

		private fun jumpByImpl(delta: Float, spring: SpringParameters, guarantee: Guarantee) {
		check(sourceValue.isNaN())

		val breakpoint = doAddBreakpointImpl(spring, guarantee)
		sourceValue = mappings.last().map(breakpoint.position) + delta
		}

		private fun continueWithImpl(mapping: Mapping, spring: SpringParameters, guarantee: Guarantee) {
		check(sourceValue.isNaN())

		doAddBreakpointImpl(spring, guarantee)
		mappings.add(mapping)
		}

		private fun toBreakpointImpl(atPosition: Float, key: BreakpointKey) {
		check(breakpointPosition.isNaN())
		check(breakpointKey == null)

		if (!targetValue.isNaN() \|\| !fractionalMapping.isNaN()) {
		check(!sourceValue.isNaN())

		val sourcePosition = breakpoints.last().position

		if (fractionalMapping.isNaN()) {
		val delta = targetValue - sourceValue
		fractionalMapping = delta / (atPosition - sourcePosition)
		} else {
		val delta = (atPosition - sourcePosition) * fractionalMapping
		targetValue = sourceValue + delta
		}

		val offset = sourceValue - (sourcePosition * fractionalMapping)

		mappings.add(Mapping.Linear(fractionalMapping, offset))
		targetValue = Float.NaN
		sourceValue = Float.NaN
		fractionalMapping = Float.NaN
		}

		breakpointPosition = atPosition
		breakpointKey = key
		}

		private fun completeImpl() {
		check(targetValue.isNaN()) { "cant specify target value for last segment" }

		if (!fractionalMapping.isNaN()) {
		check(!sourceValue.isNaN())

		val sourcePosition = breakpoints.last().position

		mappings.add(
		Mapping.Linear(
		fractionalMapping,
		sourceValue - (sourcePosition * fractionalMapping),
		)
		)
		}

		breakpoints.add(Breakpoint.maxLimit)
		}

		private fun doAddBreakpointImpl(
		springSpec: SpringParameters,
		guarantee: Guarantee,
		): Breakpoint {
		check(breakpointPosition.isFinite())
		return Breakpoint(checkNotNull(breakpointKey), breakpointPosition, springSpec, guarantee)
		.also {
		breakpoints.add(it)
		breakpointPosition = Float.NaN
		breakpointKey = null
		}
		}
		}

mechanics/tests/src/com/android/mechanics/spec/DirectionalMotionSpecBuilderTest.kt

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		/*
		* Copyright (C) 2025 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.
		*/

		package com.android.mechanics.spec

		import androidx.test.ext.junit.runners.AndroidJUnit4
		import com.android.mechanics.spring.SpringParameters
		import com.android.mechanics.testing.DirectionalMotionSpecSubject.Companion.assertThat
		import org.junit.Test
		import org.junit.runner.RunWith

		@RunWith(AndroidJUnit4::class)
		class DirectionalMotionSpecBuilderTest {

		@Test
		fun directionalSpec_buildEmptySpec() {
		val result = buildDirectionalMotionSpec()

		assertThat(result).breakpoints().isEmpty()
		assertThat(result).mappings().containsExactly(Mapping.Identity)
		}

		@Test
		fun directionalSpec_addBreakpointsAndMappings() {
		val result =
		buildDirectionalMotionSpec(Spring, Mapping.Zero) {
		mapping(breakpoint = 0f, mapping = Mapping.One, key = B1)
		mapping(breakpoint = 10f, mapping = Mapping.Two, key = B2)
		}

		assertThat(result).breakpoints().keys().containsExactly(B1, B2).inOrder()
		assertThat(result).breakpoints().withKey(B1).isAt(0f)
		assertThat(result).breakpoints().withKey(B2).isAt(10f)
		assertThat(result)
		.mappings()
		.containsExactly(Mapping.Zero, Mapping.One, Mapping.Two)
		.inOrder()
		}

		@Test
		fun directionalSpec_mappingBuilder_setsDefaultSpring() {
		val result =
		buildDirectionalMotionSpec(Spring) { constantValue(breakpoint = 10f, value = 20f) }

		assertThat(result).breakpoints().atPosition(10f).spring().isEqualTo(Spring)
		}

		@Test
		fun directionalSpec_mappingBuilder_canOverrideDefaultSpring() {
		val otherSpring = SpringParameters(stiffness = 10f, dampingRatio = 0.1f)
		val result =
		buildDirectionalMotionSpec(Spring) {
		constantValue(breakpoint = 10f, value = 20f, spring = otherSpring)
		}

		assertThat(result).breakpoints().atPosition(10f).spring().isEqualTo(otherSpring)
		}

		@Test
		fun directionalSpec_mappingBuilder_defaultsToNoGuarantee() {
		val result =
		buildDirectionalMotionSpec(Spring) { constantValue(breakpoint = 10f, value = 20f) }

		assertThat(result).breakpoints().atPosition(10f).guarantee().isEqualTo(Guarantee.None)
		}

		@Test
		fun directionalSpec_mappingBuilder_canSetGuarantee() {
		val guarantee = Guarantee.InputDelta(10f)
		val result =
		buildDirectionalMotionSpec(Spring) {
		constantValue(breakpoint = 10f, value = 20f, guarantee = guarantee)
		}

		assertThat(result).breakpoints().atPosition(10f).guarantee().isEqualTo(guarantee)
		}

		@Test
		fun directionalSpec_mappingBuilder_jumpTo_setsAbsoluteValue() {
		val result =
		buildDirectionalMotionSpec(Spring, Mapping.Fixed(99f)) {
		constantValue(breakpoint = 10f, value = 20f)
		}

		assertThat(result).breakpoints().positions().containsExactly(10f)
		assertThat(result).mappings().atOrAfter(10f).isConstantValue(20f)
		}

		@Test
		fun directionalSpec_mappingBuilder_jumpBy_setsRelativeValue() {
		val result =
		buildDirectionalMotionSpec(Spring, Mapping.Linear(factor = 0.5f)) {
		// At 10f the current value is 5f (10f * 0.5f)
		constantValueFromCurrent(breakpoint = 10f, delta = 30f)
		}

		assertThat(result).breakpoints().positions().containsExactly(10f)
		assertThat(result).mappings().atOrAfter(10f).isConstantValue(35f)
		}

		@Test
		fun directionalSpec_mappingBuilder_continueWithConstantValue_usesSourceValue() {
		val result =
		buildDirectionalMotionSpec(Spring, Mapping.Linear(factor = 0.5f)) {
		// At 5f the current value is 2.5f (5f * 0.5f)
		constantValueFromCurrent(breakpoint = 5f)
		}

		assertThat(result).mappings().atOrAfter(5f).isConstantValue(2.5f)
		}

		@Test
		fun directionalSpec_mappingBuilder_continueWithFractionalInput_matchesLinearMapping() {
		val result =
		buildDirectionalMotionSpec(Spring) {
		fractionalInput(breakpoint = 5f, from = 1f, fraction = .1f)
		}

		assertThat(result)
		.mappings()
		.atOrAfter(5f)
		.matchesLinearMapping(in1 = 5f, out1 = 1f, in2 = 15f, out2 = 2f)
		}

		@Test
		fun directionalSpec_mappingBuilder_continueWithTargetValue_matchesLinearMapping() {
		val result =
		buildDirectionalMotionSpec(Spring) {
		target(breakpoint = 5f, from = 1f, to = 20f)
		mapping(breakpoint = 30f, mapping = Mapping.Identity)
		}

		assertThat(result)
		.mappings()
		.atOrAfter(5f)
		.matchesLinearMapping(in1 = 5f, out1 = 1f, in2 = 30f, out2 = 20f)
		}

		companion object {
		val Spring = SpringParameters(stiffness = 100f, dampingRatio = 1f)
		val B1 = BreakpointKey("One")
		val B2 = BreakpointKey("Two")
		}
		}