android-34/android/view/MotionPredictor.java

/*
 * Copyright (C) 2023 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 android.view;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.content.Context;

import libcore.util.NativeAllocationRegistry;

/**
 * Calculate motion predictions.
 *
 * Feed motion events to this class in order to generate predicted future events. The prediction
 * functionality may not be available on all devices: check if a specific source is supported on a
 * given input device using {@link #isPredictionAvailable}.
 *
 * Send all of the events that were received from the system to {@link #record} to generate
 * complete, accurate predictions from {@link #predict}. When processing the returned predictions,
 * make sure to consider all of the {@link MotionEvent#getHistoricalAxisValue historical samples}.
 */
public final class MotionPredictor {

    // This is a pass-through to the native MotionPredictor object (mPtr). Do not store any state or
    // add any business logic here -- all of the implementation details should go into the native
    // MotionPredictor (except for accessing the context/resources, which have no corresponding
    // native API).

    private static class RegistryHolder {
        public static final NativeAllocationRegistry REGISTRY =
                NativeAllocationRegistry.createMalloced(
                        MotionPredictor.class.getClassLoader(),
                        nativeGetNativeMotionPredictorFinalizer());
    }

    // Pointer to the native object.
    private final long mPtr;
    // Device-specific override to enable/disable motion prediction.
    private final boolean mIsPredictionEnabled;

    /**
     * Create a new MotionPredictor for the provided {@link Context}.
     * @param context The context for the predictions
     */
    public MotionPredictor(@NonNull Context context) {
        mIsPredictionEnabled = context.getResources().getBoolean(
                com.android.internal.R.bool.config_enableMotionPrediction);
        final int offsetNanos = context.getResources().getInteger(
                com.android.internal.R.integer.config_motionPredictionOffsetNanos);
        mPtr = nativeInitialize(offsetNanos);
        RegistryHolder.REGISTRY.registerNativeAllocation(this, mPtr);
    }

    /**
     * Record a movement so that in the future, a prediction for the current gesture can be
     * generated. Only gestures from one input device at a time should be provided to an instance of
     * MotionPredictor.
     *
     * @param event The received event
     *
     * @throws IllegalArgumentException if an inconsistent MotionEvent stream is sent.
     */
    public void record(@NonNull MotionEvent event) {
        if (!mIsPredictionEnabled) {
            return;
        }
        nativeRecord(mPtr, event);
    }

    /**
     * Get a predicted event for the gesture that has been provided to {@link #record}.
     * Predictions may not reach the requested timestamp if the confidence in the prediction results
     * is low.
     *
     * @param predictionTimeNanos The time that the prediction should target, in the
     * {@link android.os.SystemClock#uptimeMillis} time base, but in nanoseconds.
     *
     * @return The predicted motion event, or `null` if predictions are not supported, or not
     * possible for the current gesture. Be sure to check the historical data in addition to the
     * latest ({@link MotionEvent#getX getX()}, {@link MotionEvent#getY getY()}) coordinates for
     * smooth prediction curves.
     */
    @Nullable
    public MotionEvent predict(long predictionTimeNanos) {
        if (!mIsPredictionEnabled) {
            return null;
        }
        return nativePredict(mPtr, predictionTimeNanos);
    }

    /**
     * Check whether a device supports motion predictions for a given source type.
     *
     * @param deviceId The input device id.
     * @param source The source of input events.
     * @return True if the current device supports predictions, false otherwise.
     *
     * @see MotionEvent#getDeviceId
     * @see MotionEvent#getSource
     */
    public boolean isPredictionAvailable(int deviceId, int source) {
        return mIsPredictionEnabled && nativeIsPredictionAvailable(mPtr, deviceId, source);
    }

    private static native long nativeInitialize(int offsetNanos);
    private static native void nativeRecord(long nativePtr, MotionEvent event);
    private static native MotionEvent nativePredict(long nativePtr, long predictionTimeNanos);
    private static native boolean nativeIsPredictionAvailable(long nativePtr, int deviceId,
            int source);
    private static native long nativeGetNativeMotionPredictorFinalizer();
}