libs/input/MotionPredictor.cpp

/*
 * Copyright (C) 2022 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.
 */

#define LOG_TAG "MotionPredictor"

#include <input/MotionPredictor.h>

#include <cinttypes>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <string>
#include <vector>

#include <android-base/strings.h>
#include <android/input.h>
#include <log/log.h>

#include <attestation/HmacKeyManager.h>
#include <input/TfLiteMotionPredictor.h>

namespace android {
namespace {

const char DEFAULT_MODEL_PATH[] = "/system/etc/motion_predictor_model.fb";
const int64_t PREDICTION_INTERVAL_NANOS =
        12500000 / 3; // TODO(b/266747937): Get this from the model.

/**
 * Log debug messages about predictions.
 * Enable this via "adb shell setprop log.tag.MotionPredictor DEBUG"
 */
bool isDebug() {
    return __android_log_is_loggable(ANDROID_LOG_DEBUG, LOG_TAG, ANDROID_LOG_INFO);
}

// Converts a prediction of some polar (r, phi) to Cartesian (x, y) when applied to an axis.
TfLiteMotionPredictorSample::Point convertPrediction(
        const TfLiteMotionPredictorSample::Point& axisFrom,
        const TfLiteMotionPredictorSample::Point& axisTo, float r, float phi) {
    const TfLiteMotionPredictorSample::Point axis = axisTo - axisFrom;
    const float axis_phi = std::atan2(axis.y, axis.x);
    const float x_delta = r * std::cos(axis_phi + phi);
    const float y_delta = r * std::sin(axis_phi + phi);
    return {.x = axisTo.x + x_delta, .y = axisTo.y + y_delta};
}

} // namespace

// --- MotionPredictor ---

MotionPredictor::MotionPredictor(nsecs_t predictionTimestampOffsetNanos, const char* modelPath,
                                 std::function<bool()> checkMotionPredictionEnabled)
      : mPredictionTimestampOffsetNanos(predictionTimestampOffsetNanos),
        mModelPath(modelPath == nullptr ? DEFAULT_MODEL_PATH : modelPath),
        mCheckMotionPredictionEnabled(std::move(checkMotionPredictionEnabled)) {}

void MotionPredictor::record(const MotionEvent& event) {
    if (!isPredictionAvailable(event.getDeviceId(), event.getSource())) {
        ALOGE("Prediction not supported for device %d's %s source", event.getDeviceId(),
              inputEventSourceToString(event.getSource()).c_str());
        return;
    }

    // Initialise the model now that it's likely to be used.
    if (!mModel) {
        mModel = TfLiteMotionPredictorModel::create(mModelPath.c_str());
    }

    TfLiteMotionPredictorBuffers& buffers =
            mDeviceBuffers.try_emplace(event.getDeviceId(), mModel->inputLength()).first->second;

    const int32_t action = event.getActionMasked();
    if (action == AMOTION_EVENT_ACTION_UP) {
        ALOGD_IF(isDebug(), "End of event stream");
        buffers.reset();
        return;
    } else if (action != AMOTION_EVENT_ACTION_DOWN && action != AMOTION_EVENT_ACTION_MOVE) {
        ALOGD_IF(isDebug(), "Skipping unsupported %s action",
                 MotionEvent::actionToString(action).c_str());
        return;
    }

    if (event.getPointerCount() != 1) {
        ALOGD_IF(isDebug(), "Prediction not supported for multiple pointers");
        return;
    }

    const int32_t toolType = event.getPointerProperties(0)->toolType;
    if (toolType != AMOTION_EVENT_TOOL_TYPE_STYLUS) {
        ALOGD_IF(isDebug(), "Prediction not supported for non-stylus tool: %s",
                 motionToolTypeToString(toolType));
        return;
    }

    for (size_t i = 0; i <= event.getHistorySize(); ++i) {
        if (event.isResampled(0, i)) {
            continue;
        }
        const PointerCoords* coords = event.getHistoricalRawPointerCoords(0, i);
        buffers.pushSample(event.getHistoricalEventTime(i),
                           {
                                   .position.x = coords->getAxisValue(AMOTION_EVENT_AXIS_X),
                                   .position.y = coords->getAxisValue(AMOTION_EVENT_AXIS_Y),
                                   .pressure = event.getHistoricalPressure(0, i),
                                   .tilt = event.getHistoricalAxisValue(AMOTION_EVENT_AXIS_TILT, 0,
                                                                        i),
                                   .orientation = event.getHistoricalOrientation(0, i),
                           });
    }

    mLastEvents.try_emplace(event.getDeviceId())
            .first->second.copyFrom(&event, /*keepHistory=*/false);
}

std::vector<std::unique_ptr<MotionEvent>> MotionPredictor::predict(nsecs_t timestamp) {
    std::vector<std::unique_ptr<MotionEvent>> predictions;

    for (const auto& [deviceId, buffer] : mDeviceBuffers) {
        if (!buffer.isReady()) {
            continue;
        }

        LOG_ALWAYS_FATAL_IF(!mModel);
        buffer.copyTo(*mModel);
        LOG_ALWAYS_FATAL_IF(!mModel->invoke());

        // Read out the predictions.
        const std::span<const float> predictedR = mModel->outputR();
        const std::span<const float> predictedPhi = mModel->outputPhi();
        const std::span<const float> predictedPressure = mModel->outputPressure();

        TfLiteMotionPredictorSample::Point axisFrom = buffer.axisFrom().position;
        TfLiteMotionPredictorSample::Point axisTo = buffer.axisTo().position;

        if (isDebug()) {
            ALOGD("deviceId: %d", deviceId);
            ALOGD("axisFrom: %f, %f", axisFrom.x, axisFrom.y);
            ALOGD("axisTo: %f, %f", axisTo.x, axisTo.y);
            ALOGD("mInputR: %s", base::Join(mModel->inputR(), ", ").c_str());
            ALOGD("mInputPhi: %s", base::Join(mModel->inputPhi(), ", ").c_str());
            ALOGD("mInputPressure: %s", base::Join(mModel->inputPressure(), ", ").c_str());
            ALOGD("mInputTilt: %s", base::Join(mModel->inputTilt(), ", ").c_str());
            ALOGD("mInputOrientation: %s", base::Join(mModel->inputOrientation(), ", ").c_str());
            ALOGD("predictedR: %s", base::Join(predictedR, ", ").c_str());
            ALOGD("predictedPhi: %s", base::Join(predictedPhi, ", ").c_str());
            ALOGD("predictedPressure: %s", base::Join(predictedPressure, ", ").c_str());
        }

        const MotionEvent& event = mLastEvents[deviceId];
        bool hasPredictions = false;
        std::unique_ptr<MotionEvent> prediction = std::make_unique<MotionEvent>();
        int64_t predictionTime = buffer.lastTimestamp();
        const int64_t futureTime = timestamp + mPredictionTimestampOffsetNanos;

        for (int i = 0; i < predictedR.size() && predictionTime <= futureTime; ++i) {
            const TfLiteMotionPredictorSample::Point point =
                    convertPrediction(axisFrom, axisTo, predictedR[i], predictedPhi[i]);
            // TODO(b/266747654): Stop predictions if confidence is < some threshold.

            ALOGD_IF(isDebug(), "prediction %d: %f, %f", i, point.x, point.y);
            PointerCoords coords;
            coords.clear();
            coords.setAxisValue(AMOTION_EVENT_AXIS_X, point.x);
            coords.setAxisValue(AMOTION_EVENT_AXIS_Y, point.y);
            // TODO(b/266747654): Stop predictions if predicted pressure is < some threshold.
            coords.setAxisValue(AMOTION_EVENT_AXIS_PRESSURE, predictedPressure[i]);

            predictionTime += PREDICTION_INTERVAL_NANOS;
            if (i == 0) {
                hasPredictions = true;
                prediction->initialize(InputEvent::nextId(), event.getDeviceId(), event.getSource(),
                                       event.getDisplayId(), INVALID_HMAC,
                                       AMOTION_EVENT_ACTION_MOVE, event.getActionButton(),
                                       event.getFlags(), event.getEdgeFlags(), event.getMetaState(),
                                       event.getButtonState(), event.getClassification(),
                                       event.getTransform(), event.getXPrecision(),
                                       event.getYPrecision(), event.getRawXCursorPosition(),
                                       event.getRawYCursorPosition(), event.getRawTransform(),
                                       event.getDownTime(), predictionTime, event.getPointerCount(),
                                       event.getPointerProperties(), &coords);
            } else {
                prediction->addSample(predictionTime, &coords);
            }

            axisFrom = axisTo;
            axisTo = point;
        }
        // TODO(b/266747511): Interpolate to futureTime?
        if (hasPredictions) {
            predictions.push_back(std::move(prediction));
        }
    }
    return predictions;
}

bool MotionPredictor::isPredictionAvailable(int32_t /*deviceId*/, int32_t source) {
    // Global flag override
    if (!mCheckMotionPredictionEnabled()) {
        ALOGD_IF(isDebug(), "Prediction not available due to flag override");
        return false;
    }

    // Prediction is only supported for stylus sources.
    if (!isFromSource(source, AINPUT_SOURCE_STYLUS)) {
        ALOGD_IF(isDebug(), "Prediction not available for non-stylus source: %s",
                 inputEventSourceToString(source).c_str());
        return false;
    }
    return true;
}

} // namespace android