Input源码解读——从"Show tabs"开始
本文基于Android T版本源码，梳理当用户在开发者选项中开启Show tabs功能后显示第点按操作的视觉反馈的原理，来进一步了解Android Input系统
Settings 写入设置
首先是设置应用(Settings)提供的开发者选项画面响应点击，将Show taps选项对应的设置Key SHOW_TOUCHES的 ON 值通过android.provder.Settings接口写入到保存系统设置数据的SettingsProvier中。
// packages/apps/Settings/src/com/android/settings/development/ShowTapsPreferenceController.java
public class ShowTapsPreferenceController extends DeveloperOptionsPreferenceController ... {
...
@Override
public boolean onPreferenceChange(Preference preference, Object newValue) {
final boolean isEnabled = (Boolean) newValue;
Settings.System.putInt(mContext.getContentResolver(),
Settings.System.SHOW_TOUCHES, isEnabled ? SETTING_VALUE_ON : SETTING_VALUE_OFF);
return true;
}
...
}
InputManagerService监听设置
负责管理输入的系统服务InputManagerService在启动之际，会监听设置中的 SHOW_TOUCHES字段的变化，在设置产生变化的时候调用native侧的代码进行处理。
// frameworks/base/services/core/java/com/android/server/input/InputManagerService.java
public class InputManagerService extends IInputManager.Stub... {
...
public void start() {
...
registerShowTouchesSettingObserver();
...
}
private void registerShowTouchesSettingObserver() {
mContext.getContentResolver().registerContentObserver(
Settings.System.getUriFor(Settings.System.SHOW_TOUCHES), true,
new ContentObserver(mHandler) {
@Override
public void onChange(boolean selfChange) {
updateShowTouchesFromSettings();
}
}, UserHandle.USER_ALL);
}
private void updateShowTouchesFromSettings() {
int setting = getShowTouchesSetting(0);
mNative.setShowTouches(setting != 0);
}
...
// frameworks/base/services/core/java/com/android/server/input/NativeInputManagerService.java
public interface NativeInputManagerService {
...
void setShowTouches(boolean enabled);
...
}
// frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp
class NativeInputManager : public virtual RefBase, ...{
...
void setShowTouches(bool enabled);
...
}
void NativeInputManager::setShowTouches(bool enabled) {
{ // acquire lock
AutoMutex _l(mLock);
if (mLocked.showTouches == enabled) {
return;
}
ALOGI("Setting show touches feature to %s.", enabled ? "enabled" : "disabled");
mLocked.showTouches = enabled;
} // release lock
mInputManager->getReader().requestRefreshConfiguration(
InputReaderConfiguration::CHANGE_SHOW_TOUCHES);
}
这里的mInputManager是InputManagerInterface对象实例，InputManager是InputManagerInterface和子类，所以通过mInputManager可以连接NativeInputManager和InputReader。
这里向负责读取事件的InputReader发出更新配置的请求，配置变更的Type为 CHANGE_SHOW_TOUCHES。
通过 InputReader 请求刷新配置
InputReader接收到配置变化的Type之后，会根据记录待刷新配置的变量 mConfigurationChangesToRefresh判断当前是否已经在刷新过程中。
如果尚未处于刷新中，则更新mConfigurationChangesToRefresh的值，并唤醒EventHub进行配置刷新。
// frameworks/native/services/inputflinger/reader/InputReader.cpp
void InputReader::requestRefreshConfiguration(uint32_t changes) {
std::scoped_lock _l(mLock);
if (changes) {
bool needWake = !mConfigurationChangesToRefresh;
mConfigurationChangesToRefresh |= changes;
if (needWake) {
mEventHub->wake();
}
}
}
EventHub 唤醒 InputReader 线程
InputManagerService过来的刷新请求最终需要InputReader线程来处理。
可是 InputReader 线程处在从EventHub中读取事件和没有事件时便调用epoll_wait进入等待状态的循环当中。
所以为了让其立即处理配置变化，需要EventHub的手动唤醒。
// frameworks/native/services/inputflinger/reader/EventHub.cpp
void EventHub::wake() {
ALOGV("wake() called");
ssize_t nWrite;
do {
nWrite = write(mWakeWritePipeFd, "W", 1);
} while (nWrite == -1 && errno == EINTR);
if (nWrite != 1 && errno != EAGAIN) {
ALOGW("Could not write wake signal: %s", strerror(errno));
}
}
size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) {
...
for (;;) {
...
int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, timeoutMillis);
...
}
...
}
InputReader线程刷新配置
EventHub唤醒后处于等待状态的getEvents会结束，之后InputReader线程会进入下次循环即loopOnce。
其首先将检查是否存在待刷新的配置变化changes，存在的话调用refreshConfigurationLocked让InputDevice去重新适配变化。
// frameworks/native/services/inputflinger/reader/InputReader.cpp
void InputReader::loopOnce() {
...
std::vector<InputDeviceInfo> inputDevices;
{ // acquire lock
...
uint32_t changes = mConfigurationChangesToRefresh;
if (changes) {
mConfigurationChangesToRefresh = 0;
timeoutMillis = 0;
refreshConfigurationLocked(changes);
} else if (mNextTimeout != LLONG_MAX) {
nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
timeoutMillis = toMillisecondTimeoutDelay(now, mNextTimeout);
}
} // release lock
size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE);
...
}
需要留意，refreshConfigurationLocked在调用InputDevice进一步处理之前需要先获取配置的变化放入mConfig中。
// frameworks/native/services/inputflinger/reader/InputReader.cpp
void InputReader::refreshConfigurationLocked(uint32_t changes) {
mPolicy->getReaderConfiguration(&mConfig);
...
if (changes & InputReaderConfiguration::CHANGE_MUST_REOPEN) {
mEventHub->requestReopenDevices();
} else {
for (auto& devicePair : mDevices) {
std::shared_ptr<InputDevice>& device = devicePair.second;
device->configure(now, &mConfig, changes);
}
}
...
}
InputDevice配置变化
InputDevice的configure需要处理很多配置变化，比如键盘布局、麦克风等。对于Show taps的变化关注调用 InputMapper的congfigure即可。
// frameworks/native/services/inputflinger/reader/InputDevice.cpp
void InputDevice::configure(nsecs_t when, const InputReaderConfiguration* config,
uint32_t changes) {
...
if (!isIgnored()) {
...
for_each_mapper([this, when, config, changes](InputMapper& mapper) {
mapper.configure(when, config, changes);
mSources |= mapper.getSources();
});
...
}
}
TouchInputMapper 进一步处理
众多输入事件的物理数据需要对应的InputMapper来转化为上层能识别的事件类型。比如识别键盘输入的 KeyboardInputMapper、识别震动的VibratorInputMapper等等。
现在的触摸屏都支持多点触控，所以是MultiTouchInputMapper来处理的。可MultiTouchInputMapper没有复写 configure()，而是沿用由父类TouchInputMapper的共通处理。
// frameworks/native/services/inputflinger/reader/mapper/TouchInputMapper.cpp
void TouchInputMapper::configure(nsecs_t when, const InputReaderConfiguration* config,
uint32_t changes) {
...
bool resetNeeded = false;
if (!changes ||
(changes &
(InputReaderConfiguration::CHANGE_DISPLAY_INFO |
InputReaderConfiguration::CHANGE_POINTER_CAPTURE |
InputReaderConfiguration::CHANGE_POINTER_GESTURE_ENABLEMENT |
InputReaderConfiguration::CHANGE_SHOW_TOUCHES |
InputReaderConfiguration::CHANGE_EXTERNAL_STYLUS_PRESENCE))) {
// Configure device sources, display dimensions, orientation and
// scaling factors.
configureInputDevice(when, &resetNeeded);
}
...
}
TouchInputMapper会依据changes的类型进行对应处理，对于SHOW_TOUCHES的变化需要调用configureInputDevice进一步处理。
创建和初始化 PointerController
configureInputDevice进行多个参数的测量和配置，其中和Show taps相关的是PointerController的创建，该类是 Mouse、Taps、Pointer location 等系统 Touch 显示的专用类。
// frameworks/native/services/inputflinger/reader/mapper/TouchInputMapper.cpp
void TouchInputMapper::configureInputDevice(nsecs_t when, bool* outResetNeeded) {
...
// Create pointer controller if needed, and keep it around if Pointer Capture is enabled to
// preserve the cursor position.
if (mDeviceMode == DeviceMode::POINTER ||
(mDeviceMode == DeviceMode::DIRECT && mConfig.showTouches) ||
(mParameters.deviceType == Parameters::DeviceType::POINTER &&
mConfig.pointerCaptureRequest.enable)) {
if (mPointerController == nullptr) {
mPointerController = getContext()->getPointerController(getDeviceId());
}
if (mConfig.pointerCaptureRequest.enable) {
mPointerController->fade(PointerControllerInterface::Transition::IMMEDIATE);
}
} else {
mPointerController.reset();
}
...
}
这里调用InputReaderContext#getPointerController，InputReader::ContextImpl是InputReaderContext的子类，所以会回调到InputReader开启PointerController的创建和初始化。
// frameworks/native/services/inputflinger/reader/InputReader.cpp
std::shared_ptr<PointerControllerInterface> InputReader::ContextImpl::getPointerController(
int32_t deviceId) {
// lock is already held by the input loop
return mReader->getPointerControllerLocked(deviceId);
}
std::shared_ptr<PointerControllerInterface> InputReader::getPointerControllerLocked(
int32_t deviceId) {
std::shared_ptr<PointerControllerInterface> controller = mPointerController.lock();
if (controller == nullptr) {
controller = mPolicy->obtainPointerController(deviceId);
mPointerController = controller;
updatePointerDisplayLocked();
}
return controller;
}
这里调用InputReaderPolicyInterface#obtainPointerController，而NativeInputManager是InputReaderPolicyInterface的子类。
// frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp
std::shared_ptr<PointerControllerInterface> NativeInputManager::obtainPointerController(
int32_t /* deviceId */) {
...
std::shared_ptr<PointerController> controller = mLocked.pointerController.lock();
if (controller == nullptr) {
ensureSpriteControllerLocked();
controller = PointerController::create(this, mLooper, mLocked.spriteController);
mLocked.pointerController = controller;
updateInactivityTimeoutLocked();
}
return controller;
}
PointerController 构建的同时需要构建持有的 MouseCursorController。
// frameworks/base/libs/input/PointerController.cpp
std::shared_ptr<PointerController> PointerController::create( ... ) {
std::shared_ptr<PointerController> controller = std::shared_ptr<PointerController>(
new PointerController(policy, looper, spriteController));
...
return controller;
}
PointerController::PointerController( ... )
: mContext(policy, looper, spriteController, *this), mCursorController(mContext) {
std::scoped_lock lock(mLock);
mLocked.presentation = Presentation::SPOT;
...
}
obtainPointerController执行完之后调用updatePointerDisplayLocked执行PointerController的初始化。
初始化 PointerController
调用PointerController的setDisplayViewport传入显示用的DisplayViewPort。
// frameworks/native/services/inputflinger/reader/InputReader.cpp
void InputReader::updatePointerDisplayLocked() {
...
std::optional<DisplayViewport> viewport =
mConfig.getDisplayViewportById(mConfig.defaultPointerDisplayId);
if (!viewport) {
...
viewport = mConfig.getDisplayViewportById(ADISPLAY_ID_DEFAULT);
}
...
controller->setDisplayViewport(*viewport);
}
setDisplayViewport需要持有的MouseCursorController进一步初始化。
// frameworks/base/libs/input/PointerController.cpp
void PointerController::setDisplayViewport(const DisplayViewport& viewport) {
...
mCursorController.setDisplayViewport(viewport, getAdditionalMouseResources);
}
MouseCursorController需要获取Display相关的参数，并执行两个重要步骤：loadResourcesLocked/updatePointerLocked
// frameworks/base/libs/input/MouseCursorController.cpp
void MouseCursorController::setDisplayViewport(const DisplayViewport& viewport,
bool getAdditionalMouseResources) {
...
// Reset cursor position to center if size or display changed.
if (oldViewport.displayId != viewport.displayId || oldDisplayWidth != newDisplayWidth ||
oldDisplayHeight != newDisplayHeight) {
float minX, minY, maxX, maxY;
if (getBoundsLocked(&minX, &minY, &maxX, &maxY)) {
mLocked.pointerX = (minX + maxX) * 0.5f;
mLocked.pointerY = (minY + maxY) * 0.5f;
// Reload icon resources for density may be changed.
loadResourcesLocked(getAdditionalMouseResources);
...
}
} else if (oldViewport.orientation != viewport.orientation) {
...
}
updatePointerLocked();
}
加载 Pointer 相关资源
// frameworks/base/libs/input/MouseCursorController.cpp
void MouseCursorController::loadResourcesLocked(bool getAdditionalMouseResources) REQUIRES(mLock) {
...
policy->loadPointerResources(&mResources, mLocked.viewport.displayId);
policy->loadPointerIcon(&mLocked.pointerIcon, mLocked.viewport.displayId);
...
}
省略诸多细节，loadPointerResources将通过InputManagerService的JNI端以及PointerIcon的JNI端创建PointerIcon实例，并读取显示的资源。
getSystemIcon则是负责的函数，其将读取系统资源里名为Pointer的Style，并读取指针对应的资源 ID。
// frameworks/base/core/java/android/view/PointerIcon.java
public static PointerIcon getSystemIcon(@NonNull Context context, int type) {
...
int typeIndex = getSystemIconTypeIndex(type);
if (typeIndex == 0) {
typeIndex = getSystemIconTypeIndex(TYPE_DEFAULT);
}
int defStyle = sUseLargeIcons ?
com.android.internal.R.style.LargePointer : com.android.internal.R.style.Pointer;
TypedArray a = context.obtainStyledAttributes(null,
com.android.internal.R.styleable.Pointer,
0, defStyle);
int resourceId = a.getResourceId(typeIndex, -1);
...
icon = new PointerIcon(type);
if ((resourceId & 0xff000000) == 0x01000000) {
icon.mSystemIconResourceId = resourceId;
} else {
icon.loadResource(context, context.getResources(), resourceId);
}
systemIcons.append(type, icon);
return icon;
}
private static int getSystemIconTypeIndex(int type) {
switch (type) {
...
case TYPE_SPOT_TOUCH:
return com.android.internal.R.styleable.Pointer_pointerIconSpotTouch;
...
default:
return 0;
}
}
资源 ID 为 pointer_spot_touch_icon。
<!-- frameworks/base/core/res/res/drawable/pointer_spot_touch_icon.xml -->
<?xml version="1.0" encoding="utf-8"?>
<pointer-icon xmlns:android="http://schemas.android.com/apk/res/android"
android:bitmap="@drawable/pointer_spot_touch"
android:hotSpotX="16dp"
android:hotSpotY="16dp" />
其指向的图片就是如下熟悉的 Spot png：pointer_spot_touch.png。之后的loadPointerIcon阶段会将该图片解析成 Bitmap 并被管理在SpriteIcon中。
而SpriteIcon在updatePointerLocked阶段会被存放到SpriteController中，等待显示的调度。
// frameworks/base/libs/input/MouseCursorController.cpp
void MouseCursorController::updatePointerLocked() REQUIRES(mLock) {
if (!mLocked.viewport.isValid()) {
return;
}
sp<SpriteController> spriteController = mContext.getSpriteController();
spriteController->openTransaction();
...
if (mLocked.updatePointerIcon) {
if (mLocked.requestedPointerType == mContext.getPolicy()->getDefaultPointerIconId()) {
mLocked.pointerSprite->setIcon(mLocked.pointerIcon);
...
}
mLocked.updatePointerIcon = false;
}
spriteController->closeTransaction();
}
显示Tap
点击的时候EventHub#getEvents会产生事件，InputReader#loopOnce会调用processEventsLocked处理事件。
// frameworks/native/services/inputflinger/reader/InputReader.cpp
void InputReader::loopOnce() {
...
size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE);
{ // acquire lock
...
if (count) {
processEventsLocked(mEventBuffer, count);
}
....
} // release lock
...
}
之后调用InputMapper开始加工事件，并在TouchInputMapper#cookAndDispatch的时候调用updateTouchSpots更新 PointerController的一些参数。
// frameworks/native/services/inputflinger/reader/mapper/TouchInputMapper.cpp
void TouchInputMapper::updateTouchSpots() {
...
mPointerController->setPresentation(PointerControllerInterface::Presentation::SPOT);
mPointerController->fade(PointerControllerInterface::Transition::GRADUAL);
mPointerController->setButtonState(mCurrentRawState.buttonState);
setTouchSpots(mCurrentCookedState.cookedPointerData.pointerCoords,
mCurrentCookedState.cookedPointerData.idToIndex,
mCurrentCookedState.cookedPointerData.touchingIdBits, mViewport.displayId);
}
其中比较关键的setTouchSpots是显示Taps的关键步骤，准备 x、y 坐标和压力值。
在 Reader 而不是 Dispatch、更不是 ViewRootImpl 的时候处理的原因在于：Read 到事件即显示可以更早地响，同时不用占用 App 进程。
// frameworks/native/services/inputflinger/reader/mapper/TouchInputMapper.cpp
void TouchInputMapper::setTouchSpots(const PointerCoords* spotCoords, const uint32_t* spotIdToIndex,
BitSet32 spotIdBits, int32_t displayId) {
std::array<PointerCoords, MAX_POINTERS> outSpotCoords{};
for (BitSet32 idBits(spotIdBits); !idBits.isEmpty();) {
const uint32_t index = spotIdToIndex[idBits.clearFirstMarkedBit()];
float x = spotCoords[index].getX();
float y = spotCoords[index].getY();
float pressure = spotCoords[index].getAxisValue(AMOTION_EVENT_AXIS_PRESSURE);
...
}
mPointerController->setSpots(outSpotCoords.data(), spotIdToIndex, spotIdBits, displayId);
}
其后PointerController会通过TouchSpotController创建Spot实例向其发送updateSprite请求。最后回调 SpriteController调用setIcon处理。
// frameworks/base/libs/input/TouchSpotController.cpp
void TouchSpotController::Spot::updateSprite(const SpriteIcon* icon, float x, float y,
int32_t displayId) {
sprite->setLayer(Sprite::BASE_LAYER_SPOT + id);
...
if (icon != mLastIcon) {
mLastIcon = icon;
if (icon) {
sprite->setIcon(*icon);
sprite->setVisible(true);
} else {
sprite->setVisible(false);
}
}
}
// frameworks/base/libs/input/SpriteController.cpp
void SpriteController::SpriteImpl::setIcon(const SpriteIcon& icon) {
AutoMutex _l(mController->mLock);
...
invalidateLocked(dirty);
}
void SpriteController::SpriteImpl::invalidateLocked(uint32_t dirty) {
...
if (!wasDirty) {
mController->invalidateSpriteLocked(this);
}
}
void SpriteController::invalidateSpriteLocked(const sp<SpriteImpl>& sprite) {
bool wasEmpty = mLocked.invalidatedSprites.isEmpty();
mLocked.invalidatedSprites.push(sprite);
if (wasEmpty) {
if (mLocked.transactionNestingCount != 0) {
mLocked.deferredSpriteUpdate = true;
} else {
mLooper->sendMessage(mHandler, Message(MSG_UPDATE_SPRITES));
}
}
}
MSG_UPDATE_SPRITES经过 Handler 回调doUpdateSprites，将取出封装在SpriteUpdate中的SpriteIcon并执行 draw。
// frameworks/base/libs/input/SpriteController.cpp
void SpriteController::doUpdateSprites() {
...
for (size_t i = 0; i < numSprites; i++) {
SpriteUpdate& update = updates.editItemAt(i);
if ((update.state.dirty & DIRTY_BITMAP) && update.state.surfaceDrawn) {
update.state.surfaceDrawn = false;
update.surfaceChanged = surfaceChanged = true;
}
if (update.state.surfaceControl != NULL && !update.state.surfaceDrawn
&& update.state.wantSurfaceVisible()) {
sp<Surface> surface = update.state.surfaceControl->getSurface();
if (update.state.icon.draw(surface)) {
update.state.surfaceDrawn = true;
update.surfaceChanged = surfaceChanged = true;
}
}
}
...
updates.clear();
}
最后，SpriteIcon将取出Bitmap描画到Surface的Canvas上去。
// frameworks/base/libs/input/SpriteIcon.cpp
bool SpriteIcon::draw(sp<Surface> surface) const {
...
graphics::Paint paint;
paint.setBlendMode(ABLEND_MODE_SRC);
graphics::Canvas canvas(outBuffer, (int32_t)surface->getBuffersDataSpace());
canvas.drawBitmap(bitmap, 0, 0, &paint);
...
status = surface->unlockAndPost();
if (status) {
ALOGE("Error %d unlocking and posting sprite surface after drawing.", status);
}
return !status;
}
总体流程
通过一个框图简单回顾一下整个流程。
可以看到，简简单单的 Show taps 功能，从设置、配置、刷新再到显示，经历了多个进程、多个模块的协力。
涉及的Input核心逻辑框图
