https://www.jianshu.com/p/2bff4ecd86c9 已经大概说了下Android Input的整体流程，但是还有些小细节并没有详细说，而这篇文章主要讲了Input是如何加入输入设备，以及input是如何解析输入设备上报的事件的。
EventHub::getEvents()在第一次进入的时候，会根据 mNeedToScanDevices 的值去决定是否去扫描设备，而 mNeedToScanDevices 默认是为true的
if (mNeedToScanDevices) {
mNeedToScanDevices = false;
scanDevicesLocked();
mNeedToSendFinishedDeviceScan = true;
}
scanDevicesLocked()这个函数完成两件事, 一个是去扫描 /dev/input 下所有的输入设备,另一个是创建一个 VIRTUAL KEYBOARD 设备,顾名思义，虚拟键盘。
void EventHub::scanDevicesLocked() {
status_t res = scanDirLocked(DEVICE_PATH);
if(res < 0) {
ALOGE("scan dir failed for %s\n", DEVICE_PATH);
}
if (mDevices.indexOfKey(VIRTUAL_KEYBOARD_ID) < 0) {
createVirtualKeyboardLocked();
}
}
scanDirLocked函数会通过openDeviceLocked打开 /dev/input 下的每一个输入设备来决定是否将该设备加入到input框架中去。
如在 pixel 手机中, 有如下的输入设备
sailfish:/ # ls /dev/input
event0 event1 event2 event3 event4 event5 event6 mice
openDeviceLocked()函数人主要功能有
-
是通过 ioctl 向驱动查询输入设备的相关信息 如 device name, driver version, device identifier(vendor/version/bus ...) 等， 如果查询失败，则说明驱动有问题，input就不会将该输入设备加入到input框架当中。
-
如果驱动没问题，则通过loadConfigurationLocked 去查找并加载configure文件 如果有configure文件，则通过 PropertyMap::load将configure文件里的内容加载进来
-
通过 ioctl 去查询该 输入设备上报什么事件, 如 key/ abs /rel ...等等事件
ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(device->keyBitmask)), device->keyBitmask);
ioctl(fd, EVIOCGBIT(EV_ABS, sizeof(device->absBitmask)), device->absBitmask);
ioctl(fd, EVIOCGBIT(EV_REL, sizeof(device->relBitmask)), device->relBitmask);
ioctl(fd, EVIOCGBIT(EV_SW, sizeof(device->swBitmask)), device->swBitmask);
ioctl(fd, EVIOCGBIT(EV_LED, sizeof(device->ledBitmask)), device->ledBitmask);
ioctl(fd, EVIOCGBIT(EV_FF, sizeof(device->ffBitmask)), device->ffBitmask);
ioctl(fd, EVIOCGPROP(sizeof(device->propBitmask)), device->propBitmask);
-
根据这些上报的事件类型，设备device的 classes, 如INPUT_DEVICE_CLASS_KEYBOARD, 并加载对应的 key layout map 和 key character map
-
最后再通过
void EventHub::addDeviceLocked(Device* device) {
mDevices.add(device->id, device);
device->next = mOpeningDevices;
mOpeningDevices = device;
}
加入到 mDevices 和 mOpeningDevices中。
这里以pixel手机的触摸屏输入设备为例
# cat gpio-keys.kl
key 116 POWER
key 115 VOLUME_UP
key 114 VOLUME_DOWN
EventHub发现了输入设备后，紧接着向InputReader上报关于设备加入了
while (mOpeningDevices != NULL) {
Device* device = mOpeningDevices;
mOpeningDevices = device->next;
event->when = now;
event->deviceId = device->id == mBuiltInKeyboardId ? 0 : device->id;
event->type = DEVICE_ADDED;
event += 1;
mNeedToSendFinishedDeviceScan = true;
if (--capacity == 0) {
break;
}
}
1.1 小节在扫描设备完后将设备加入了 mClosingDevices, 此时Eventhub将mClosingDevices所构成的链表依次加入到 event (DEVICE_ADDED)
InputReader在收到事件后
case EventHubInterface::DEVICE_ADDED:
addDeviceLocked(rawEvent->when, rawEvent->deviceId);
break;
调用 addDeviceLocked 生成 InputDevice 并加入到 InputReader里的 mDevices中
InputReader在收到输入设备的事件后，会调用 processEventsForDeviceLocked 去处理输入事件
void InputReader::processEventsForDeviceLocked(int32_t deviceId,
const RawEvent* rawEvents, size_t count) {
ssize_t deviceIndex = mDevices.indexOfKey(deviceId);
InputDevice* device = mDevices.valueAt(deviceIndex);
device->process(rawEvents, count);
}
最终又会调用 InputDevice::process 去处理这些输入事件
void InputDevice::process(const RawEvent* rawEvents, size_t count) {
// Process all of the events in order for each mapper.
// We cannot simply ask each mapper to process them in bulk because mappers may
// have side-effects that must be interleaved. For example, joystick movement events and
// gamepad button presses are handled by different mappers but they should be dispatched
// in the order received.
size_t numMappers = mMappers.size();
for (const RawEvent* rawEvent = rawEvents; count--; rawEvent++) {
if (mDropUntilNextSync) {
...
} else if (rawEvent->type == EV_SYN && rawEvent->code == SYN_DROPPED) {
...
} else {
for (size_t i = 0; i < numMappers; i++) {
InputMapper* mapper = mMappers[i];
mapper->process(rawEvent);
}
}
}
}
当按一次power键后，EventHub就获得了两个事件，如下log所示
void KeyboardInputMapper::process(const RawEvent* rawEvent) {
switch (rawEvent->type) {
case EV_KEY: {
int32_t scanCode = rawEvent->code;
int32_t usageCode = mCurrentHidUsage;
mCurrentHidUsage = 0;
if (isKeyboardOrGamepadKey(scanCode)) {
processKey(rawEvent->when, rawEvent->value != 0, scanCode, usageCode);
}
break;
}
case EV_MSC: {
if (rawEvent->code == MSC_SCAN) {
mCurrentHidUsage = rawEvent->value;
}
break;
}
case EV_SYN: {
if (rawEvent->code == SYN_REPORT) {
mCurrentHidUsage = 0;
}
}
}
}
- 单点触摸
第一个 bunch
type = 3 对应的是 EV_ABS, 然后它的 code 分别为 0x39(ABS_MT_TRACKING_ID), 0x35(ABS_MT_POSITION_X), 0x36(ABS_MT_POSITION_Y), 0x3a(ABS_MT_PRESSURE) type = 0 对应的是 EV_SYN, 其实 EV_SYN 表示一组输入事件结束
第二个 bunch
type = 3, code 分别是 0x31(ABS_MT_TOUCH_MINOR), 0x3a(ABS_MT_PRESSURE)
第三个 bunch
最后 bunch
从上面的连续的bunch, 可以看出，第一个bunch给出来触摸点的位置以及压力，后面的bunch只有压力的改变。也就是手指点击后并没有移动过，否则会有新的position上报
现在来看下代码
void MultiTouchInputMapper::process(const RawEvent* rawEvent) {
TouchInputMapper::process(rawEvent);
mMultiTouchMotionAccumulator.process(rawEvent);
}
void TouchInputMapper::process(const RawEvent* rawEvent) {
mCursorButtonAccumulator.process(rawEvent);
mCursorScrollAccumulator.process(rawEvent);
mTouchButtonAccumulator.process(rawEvent);
if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {
sync(rawEvent->when);
}
}
void MultiTouchMotionAccumulator::process(const RawEvent* rawEvent) {
if (rawEvent->type == EV_ABS) {
...
if (mCurrentSlot < 0 || size_t(mCurrentSlot) >= mSlotCount) {
...
} else {
Slot* slot = &mSlots[mCurrentSlot];
switch (rawEvent->code) {
case ABS_MT_POSITION_X:
slot->mInUse = true;
slot->mAbsMTPositionX = rawEvent->value;
break;
case ABS_MT_POSITION_Y:
slot->mInUse = true;
slot->mAbsMTPositionY = rawEvent->value;
break;
case ABS_MT_TOUCH_MAJOR:
slot->mInUse = true;
slot->mAbsMTTouchMajor = rawEvent->value;
break;
...
}
由代码可知 MultiTouchMotionAccumulator 就是将每个 bunch 的事件放到一个 Slot, 在这个单点触摸的例子中，每一个bunch, InputReader dispatch一次，下一个bunch会基于上一个bunch的值，如本例中第二个bunch，本来没有x, y的值，但是由于这次是继承上一次的x, y, 所以 x, y是上一次的值，改变的是仅仅是 pressure的值，其它值未变。
最后经过一系列的运算，通过 dispatchMotion 将触屏事件发送出去
void TouchInputMapper::process(const RawEvent* rawEvent) {
...
//每一个bunch都以EV_SYN结束，然后sync
if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {
sync(rawEvent->when);
}
}
sync -> syncTouch -> processRawTouches -> cookAndDispatch -> dispatchTouches -> dispatchMotion
- 多点触摸
第一个bunch
