Add `MotionBuilderContext` to encapsulate density and motion scheme.

/*

 * 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.

 */

@file:OptIn(ExperimentalMaterial3ExpressiveApi::class)

package com.android.mechanics.spec.builder

import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi

import androidx.compose.material3.MaterialTheme

import androidx.compose.material3.MotionScheme

import androidx.compose.runtime.Composable

import androidx.compose.runtime.remember

import androidx.compose.ui.platform.LocalDensity

import androidx.compose.ui.unit.Density

import com.android.mechanics.spring.SpringParameters

/**

 * Device / scheme specific context for building motion specs.

 *

 * See go/motion-system.

 */

interface MotionBuilderContext : Density {

    /**

     * Spatial spring tokens.

     *

     * Used for animations that move something on screen, for example the x and y position,

     * rotation, size, rounded corners.

     *

     * See go/motion-system#b99b0d12-e9c8-4605-96dd-e3f17bfe9538

     */

    val spatial: MaterialSprings

    /**

     * Effects spring tokens.

     *

     * Used to animate properties such as color and opacity animations.

     *

     * See go/motion-system#142c8835-7474-4f74-b2eb-e1187051ec1f

     */

    val effects: MaterialSprings

    companion object {

        /** Default threshold for effect springs. */

        const val StableThresholdEffects = 0.01f

        /**

         * Default threshold for spatial springs.

         *

         * Cuts off when remaining oscillations are below 1px

         */

        const val StableThresholdSpatial = 1f

    }

}

/** Material spring tokens, see go/motion-system##63b14c00-d049-4d3e-b8b6-83d8f524a8db for usage. */

data class MaterialSprings(

    val default: SpringParameters,

    val fast: SpringParameters,

    val slow: SpringParameters,

    val stabilityThreshold: Float,

)

/** [MotionBuilderContext] based on the current [Density] and [MotionScheme]. */

@Composable

fun rememberMotionBuilderContext(): MotionBuilderContext {

    val density = LocalDensity.current

    val motionScheme = MaterialTheme.motionScheme

    return remember(density, motionScheme) { ComposeMotionBuilderContext(motionScheme, density) }

}

internal class ComposeMotionBuilderContext(motionScheme: MotionScheme, density: Density) :

    MotionBuilderContext, Density by density {

    override val spatial =

        MaterialSprings(

            SpringParameters(motionScheme.defaultSpatialSpec<Float>()),

            SpringParameters(motionScheme.fastSpatialSpec<Float>()),

            SpringParameters(motionScheme.slowSpatialSpec<Float>()),

            MotionBuilderContext.StableThresholdSpatial,

        )

    override val effects =

        MaterialSprings(

            SpringParameters(motionScheme.defaultEffectsSpec<Float>()),

            SpringParameters(motionScheme.fastEffectsSpec<Float>()),

            SpringParameters(motionScheme.slowEffectsSpec<Float>()),

            MotionBuilderContext.StableThresholdEffects,

        )

}

// 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 {

    default_applicable_licenses: ["Android-Apache-2.0"],

    default_team: "trendy_team_motion",

}

android_library {

    name: "mechanics-testing",

    manifest: "AndroidManifest.xml",

    srcs: [

        "src/**/*.kt",

    ],

    static_libs: [

        "//frameworks/libs/systemui/mechanics:mechanics",

        "platform-test-annotations",

        "PlatformMotionTestingCompose",

        "androidx.compose.runtime_runtime",

        "androidx.compose.ui_ui-test-junit4",

        "testables",

        "truth",

    ],

}

<?xml version="1.0" encoding="utf-8"?>

<!--

  ~ 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.

  -->

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.android.mechanics.testing">

</manifest>

/*

 * 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.testing

import androidx.compose.ui.unit.Density

import com.android.mechanics.spec.builder.MaterialSprings

import com.android.mechanics.spec.builder.MotionBuilderContext

import com.android.mechanics.spring.SpringParameters

/**

 * [MotionBuilderContext] implementation for unit tests.

 *

 * Only use when the specifics of the spring parameters do not matter for the test.

 *

 * While the values are copied from the current material motion tokens, this can (and likely will)

 * get out of sync with the material tokens, and is not intended reflect the up-to-date tokens, but

 * provide a stable definitions of "some" spring parameters.

 */

class FakeMotionSpecBuilderContext(density: Float = 1f) :

    MotionBuilderContext, Density by Density(density) {

    override val spatial =

        MaterialSprings(

            SpringParameters(700.0f, 0.9f),

            SpringParameters(1400.0f, 0.9f),

            SpringParameters(300.0f, 0.9f),

            MotionBuilderContext.StableThresholdSpatial,

        )

    override val effects =

        MaterialSprings(

            SpringParameters(1600.0f, 1.0f),

            SpringParameters(3800.0f, 1.0f),

            SpringParameters(800.0f, 1.0f),

            MotionBuilderContext.StableThresholdEffects,

        )

    companion object {

        val Default = FakeMotionSpecBuilderContext()

    }

}

        "androidx.compose.foundation_foundation-layout",

        // ":mechanics_tests" dependencies

        "//frameworks/libs/systemui/mechanics:mechanics-testing",

        "androidx.compose.animation_animation-core",

        "platform-test-annotations",

        "PlatformMotionTestingCompose",