[Android Input系统]MotionEvent的序列化传送

这里从云游戏的触控操作看起，

PC端的客户端支持按键和鼠标滑动操作，手机上的云游戏客户端则是和手机游戏一样的touch触控，客户端的touch操作是怎样处理给服务端的呢，猜测是把touch操作“实时”的传送给了服务器，Android服务器上把这些数据转换为相应的MotionEvent事件。

MotionEvent主要包含触控点的信息，由于其实现了Parcelable接口，所以可以使用Parcel来进行序列化保存和传输。

public final class MotionEvent extends InputEvent implements Parcelable

这里再进一步考虑一下，在Input事件分发的时候，InputDispatcher把input事件通过InputChannel发送给对应的应用进程的时候，是怎样传送input事件数据的呢，

在frameworks/native/services/inputflinger/InputDispatcher.cpp中有


1999void InputDispatcher::startDispatchCycleLocked(nsecs_t currentTime,
2000        const sp<Connection>& connection) {
2001#if DEBUG_DISPATCH_CYCLE
2002    ALOGD("channel '%s' ~ startDispatchCycle",
2003            connection->getInputChannelName().c_str());
2004#endif
2005
2006    while (connection->status == Connection::STATUS_NORMAL
2007            && !connection->outboundQueue.isEmpty()) {
2008        DispatchEntry* dispatchEntry = connection->outboundQueue.head;
2009        dispatchEntry->deliveryTime = currentTime;
2010
2011        // Publish the event.
2012        status_t status;
2013        EventEntry* eventEntry = dispatchEntry->eventEntry;
2014        switch (eventEntry->type) {
2015        case EventEntry::TYPE_KEY: {
2016            KeyEntry* keyEntry = static_cast<KeyEntry*>(eventEntry);
2017
2018            // Publish the key event.
2019            status = connection->inputPublisher.publishKeyEvent(dispatchEntry->seq,
2020                    keyEntry->deviceId, keyEntry->source,
2021                    dispatchEntry->resolvedAction, dispatchEntry->resolvedFlags,
2022                    keyEntry->keyCode, keyEntry->scanCode,
2023                    keyEntry->metaState, keyEntry->repeatCount, keyEntry->downTime,
2024                    keyEntry->eventTime);
2025            break;
2026        }
2027
2028        case EventEntry::TYPE_MOTION: {
2029            MotionEntry* motionEntry = static_cast<MotionEntry*>(eventEntry);
2030
2031            PointerCoords scaledCoords[MAX_POINTERS];
2032            const PointerCoords* usingCoords = motionEntry->pointerCoords;
2033
2034            // Set the X and Y offset depending on the input source.
2035            float xOffset, yOffset;
2036            if ((motionEntry->source & AINPUT_SOURCE_CLASS_POINTER)
2037                    && !(dispatchEntry->targetFlags & InputTarget::FLAG_ZERO_COORDS)) {
2038                float scaleFactor = dispatchEntry->scaleFactor;
2039                xOffset = dispatchEntry->xOffset * scaleFactor;
2040                yOffset = dispatchEntry->yOffset * scaleFactor;
2041                if (scaleFactor != 1.0f) {
2042                    for (uint32_t i = 0; i < motionEntry->pointerCount; i++) {
2043                        scaledCoords[i] = motionEntry->pointerCoords[i];
2044                        scaledCoords[i].scale(scaleFactor);
2045                    }
2046                    usingCoords = scaledCoords;
2047                }
2048            } else {
2049                xOffset = 0.0f;
2050                yOffset = 0.0f;
2051
2052                // We don't want the dispatch target to know.
2053                if (dispatchEntry->targetFlags & InputTarget::FLAG_ZERO_COORDS) {
2054                    for (uint32_t i = 0; i < motionEntry->pointerCount; i++) {
2055                        scaledCoords[i].clear();
2056                    }
2057                    usingCoords = scaledCoords;
2058                }
2059            }
2060
2061            // Publish the motion event.
2062            status = connection->inputPublisher.publishMotionEvent(dispatchEntry->seq,
2063                    motionEntry->deviceId, motionEntry->source, motionEntry->displayId,
2064                    dispatchEntry->resolvedAction, motionEntry->actionButton,
2065                    dispatchEntry->resolvedFlags, motionEntry->edgeFlags,
2066                    motionEntry->metaState, motionEntry->buttonState,
2067                    xOffset, yOffset, motionEntry->xPrecision, motionEntry->yPrecision,
2068                    motionEntry->downTime, motionEntry->eventTime,
2069                    motionEntry->pointerCount, motionEntry->pointerProperties,
2070                    usingCoords);
2071            break;
2072        }

调用到inputPublisher.publishMotionEvent


284status_t InputPublisher::publishMotionEvent(
285        uint32_t seq,
286        int32_t deviceId,
287        int32_t source,
288        int32_t displayId,
289        int32_t action,
290        int32_t actionButton,
291        int32_t flags,
292        int32_t edgeFlags,
293        int32_t metaState,
294        int32_t buttonState,
295        float xOffset,
296        float yOffset,
297        float xPrecision,
298        float yPrecision,
299        nsecs_t downTime,
300        nsecs_t eventTime,
301        uint32_t pointerCount,
302        const PointerProperties* pointerProperties,
303        const PointerCoords* pointerCoords) {
304#if DEBUG_TRANSPORT_ACTIONS
305    ALOGD("channel '%s' publisher ~ publishMotionEvent: seq=%u, deviceId=%d, source=0x%x, "
306            "action=0x%x, actionButton=0x%08x, flags=0x%x, edgeFlags=0x%x, "
307            "metaState=0x%x, buttonState=0x%x, xOffset=%f, yOffset=%f, "
308            "xPrecision=%f, yPrecision=%f, downTime=%" PRId64 ", eventTime=%" PRId64 ", "
309            "pointerCount=%" PRIu32,
310            mChannel->getName().c_str(), seq,
311            deviceId, source, action, actionButton, flags, edgeFlags, metaState, buttonState,
312            xOffset, yOffset, xPrecision, yPrecision, downTime, eventTime, pointerCount);
313#endif
314
315    if (!seq) {
316        ALOGE("Attempted to publish a motion event with sequence number 0.");
317        return BAD_VALUE;
318    }
319
320    if (pointerCount > MAX_POINTERS || pointerCount < 1) {
321        ALOGE("channel '%s' publisher ~ Invalid number of pointers provided: %" PRIu32 ".",
322                mChannel->getName().c_str(), pointerCount);
323        return BAD_VALUE;
324    }
325
326    InputMessage msg;
327    msg.header.type = InputMessage::TYPE_MOTION;
328    msg.body.motion.seq = seq;
329    msg.body.motion.deviceId = deviceId;
330    msg.body.motion.source = source;
331    msg.body.motion.displayId = displayId;
332    msg.body.motion.action = action;
333    msg.body.motion.actionButton = actionButton;
334    msg.body.motion.flags = flags;
335    msg.body.motion.edgeFlags = edgeFlags;
336    msg.body.motion.metaState = metaState;
337    msg.body.motion.buttonState = buttonState;
338    msg.body.motion.xOffset = xOffset;
339    msg.body.motion.yOffset = yOffset;
340    msg.body.motion.xPrecision = xPrecision;
341    msg.body.motion.yPrecision = yPrecision;
342    msg.body.motion.downTime = downTime;
343    msg.body.motion.eventTime = eventTime;
344    msg.body.motion.pointerCount = pointerCount;
345    for (uint32_t i = 0; i < pointerCount; i++) {
346        msg.body.motion.pointers[i].properties.copyFrom(pointerProperties[i]);
347        msg.body.motion.pointers[i].coords.copyFrom(pointerCoords[i]);
348    }
349    return mChannel->sendMessage(&msg);
350}

input事件被转换成InputMessage来进行传送


151status_t InputChannel::sendMessage(const InputMessage* msg) {
152    size_t msgLength = msg->size();
153    ssize_t nWrite;
154    do {
155        nWrite = ::send(mFd, msg, msgLength, MSG_DONTWAIT | MSG_NOSIGNAL);
156    } while (nWrite == -1 && errno == EINTR);
157
158    if (nWrite < 0) {
159        int error = errno;
160#if DEBUG_CHANNEL_MESSAGES
161        ALOGD("channel '%s' ~ error sending message of type %d, errno=%d", mName.c_str(),
162                msg->header.type, error);
163#endif
164        if (error == EAGAIN || error == EWOULDBLOCK) {
165            return WOULD_BLOCK;
166        }
167        if (error == EPIPE || error == ENOTCONN || error == ECONNREFUSED || error == ECONNRESET) {
168            return DEAD_OBJECT;
169        }
170        return -error;
171    }
172
173    if (size_t(nWrite) != msgLength) {
174#if DEBUG_CHANNEL_MESSAGES
175        ALOGD("channel '%s' ~ error sending message type %d, send was incomplete",
176                mName.c_str(), msg->header.type);
177#endif
178        return DEAD_OBJECT;
179    }
180
181#if DEBUG_CHANNEL_MESSAGES
182    ALOGD("channel '%s' ~ sent message of type %d", mName.c_str(), msg->header.type);
183#endif
184    return OK;
185}

接收InputMessage数据的socket处理如下：


187status_t InputChannel::receiveMessage(InputMessage* msg) {
188    ssize_t nRead;
189    do {
190        nRead = ::recv(mFd, msg, sizeof(InputMessage), MSG_DONTWAIT);
191    } while (nRead == -1 && errno == EINTR);
192
193    if (nRead < 0) {
194        int error = errno;
195#if DEBUG_CHANNEL_MESSAGES
196        ALOGD("channel '%s' ~ receive message failed, errno=%d", mName.c_str(), errno);
197#endif
198        if (error == EAGAIN || error == EWOULDBLOCK) {
199            return WOULD_BLOCK;
200        }
201        if (error == EPIPE || error == ENOTCONN || error == ECONNREFUSED) {
202            return DEAD_OBJECT;
203        }
204        return -error;
205    }
206
207    if (nRead == 0) { // check for EOF
208#if DEBUG_CHANNEL_MESSAGES
209        ALOGD("channel '%s' ~ receive message failed because peer was closed", mName.c_str());
210#endif
211        return DEAD_OBJECT;
212    }
213
214    if (!msg->isValid(nRead)) {
215#if DEBUG_CHANNEL_MESSAGES
216        ALOGD("channel '%s' ~ received invalid message", mName.c_str());
217#endif
218        return BAD_VALUE;
219    }
220
221#if DEBUG_CHANNEL_MESSAGES
222    ALOGD("channel '%s' ~ received message of type %d", mName.c_str(), msg->header.type);
223#endif
224    return OK;
225}
226
227sp<InputChannel> InputChannel::dup() const {
228    int fd = ::dup(getFd());
229    return fd >= 0 ? new InputChannel(getName(), fd) : NULL;
230}