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Input系统之InputReader处理触摸事件案例

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手机一般有两种类型的输入设备。一种是键盘类型的输入设备,通常它包含电源键和音量下键。另一种是触摸类型的输入设备,触摸屏就属于这种类型。

键盘类型的输入设备一般都是产生按键事件,前面已经用几篇文章,分析了按键事件的分发流程。

触摸类型的输入设备一般都是产生触摸事件,本文就开始分析触摸事件的分发流程。

1. InputMapper 处理触摸事件

Input系统: InputReader 处理按键事件 可知,InputReader 从 EventHub 获取到事件后,最终把事件交给 InputMapper 进行处理。

InputMapperKeyboardInputMapperTouchInputMapperSingleTouchInputMapperMultiTouchInputMapper

对于键盘类型的输入设备,它的按键事件由 KeyboardInputManager 处理。对于触摸类型的输入设备,如果设备支持多点触摸,它的触摸事件由 MultiTouchInputMapper 处理,而如果只支持单点触摸,它的触摸事件由 SingleTouchInputMapper 处理。

通常,手机上的触摸屏都是支持多点触摸的,那么就看看 MultiTouchInputMapper 处理触摸事件的流程

void MultiTouchInputMapper::process(const RawEvent* rawEvent) {
    // 2. 调用父类处理同步事件(EV_SYN SYN_REPORT)
    TouchInputMapper::process(rawEvent);
    // 1. 使用累加器收集同步事件之前的每一个手指的触控点信息
    mMultiTouchMotionAccumulator.process(rawEvent);
}

为了方便大家理解这里的处理过程,我展示一段在触摸屏上滑动手指所产生的触摸事件序列

/dev/input/event4: EV_ABS       ABS_MT_POSITION_X    00000336            
/dev/input/event4: EV_ABS       ABS_MT_POSITION_Y    0000017f 
/dev/input/event4: EV_SYN       SYN_REPORT           00000000 
/dev/input/event4: EV_ABS       ABS_MT_POSITION_X    00000333            
/dev/input/event4: EV_ABS       ABS_MT_POSITION_Y    00000184  
/dev/input/event4: EV_SYN       SYN_REPORT           00000000   
/dev/input/event4: EV_ABS       ABS_MT_POSITION_X    0000032f            
/dev/input/event4: EV_ABS       ABS_MT_POSITION_Y    00000188   
/dev/input/event4: EV_SYN       SYN_REPORT           00000000

对于每一次的触摸事件,例如手指按下或者移动,驱动会先上报它的信息事件,例如 x, y 坐标事件,再加上一个同步事件(SYN_REPORT)。

那么,MultiTouchInputMapper 处理触摸事件的过程就很好理解了,如下

2. 收集触摸事件信息

在分析累加器收集触摸事件信息之前,首先得理解多点触摸协议,也就是 A / B 协议。B 协议也叫 slot 协议,下面简单介绍下这个协议。

当第一个手指按下时,会有如下事件序列

EV_ABS       ABS_MT_SLOT          00000000
EV_ABS       ABS_MT_TRACKING_ID   00000000            
EV_ABS       ABS_MT_POSITION_X    000002ea            
EV_ABS       ABS_MT_POSITION_Y    00000534
EV_SYN       SYN_REPORT           00000000 

事件 ABS_MT_SLOT,表明触摸信息事件,是由哪个槽(slot)进行上报的。一个手指产生的触摸事件,只能由同一个槽进行上报。

事件 ABS_MT_TRACKING_ID ,表示手指ID。手指 ID 才能唯一代表一个手指,槽的 ID 并不能代表一个手指。因为假如一个手指抬起,另外一个手指按下,这两个手指的事件可能由同一个槽进行上报,但是手指 ID 肯定是不一样的。

事件 ABS_MT_POSITION_X 和 ABS_MT_POSITION_Y 表示触摸点的 x, y 坐标值。

事件 SYN_REPORT 是同步事件,它表示系统需要同步并处理之前的事件。

当第一个手指移动时,会有如下事件

EV_ABS       ABS_MT_POSITION_X    000002ec            
EV_ABS       ABS_MT_POSITION_Y    00000526    
EV_SYN       SYN_REPORT           00000000 

此时没有指定 ABS_MT_SLOT 事件和 ABS_MT_TRACKING_ID 事件,默认使用前面的值,因为此时只有一个手指。

当第二个手指按下时,会有如下事件

EV_ABS       ABS_MT_SLOT          00000001            
EV_ABS       ABS_MT_TRACKING_ID   00000001            
EV_ABS       ABS_MT_POSITION_X    00000470            
EV_ABS       ABS_MT_POSITION_Y    00000475       
EV_SYN       SYN_REPORT           00000000 

很简单,第二个手指的事件,由另外一个槽进行上报。

当两个手指同时移动时,会有如下事件

EV_ABS       ABS_MT_SLOT          00000000            
EV_ABS       ABS_MT_POSITION_Y    000004e0            
EV_ABS       ABS_MT_SLOT          00000001            
EV_ABS       ABS_MT_POSITION_X    0000046f            
EV_ABS       ABS_MT_POSITION_Y    00000414   
EV_SYN       SYN_REPORT           00000000 

通过指定槽,就可以清晰看到事件由哪个槽进行上报,从而就可以区分出两个手指产生的事件。

当其中一个手指抬起时,会有如下事件

EV_ABS       ABS_MT_SLOT          00000000  
// 注意,ABS_MT_TRACKING_ID 的值为 -1
EV_ABS       ABS_MT_TRACKING_ID   ffffffff            
EV_ABS       ABS_MT_SLOT          00000001            
EV_ABS       ABS_MT_POSITION_Y    000003ee  
EV_SYN       SYN_REPORT           00000000  

当一个手指抬起时,ABS_MT_TRACKING_ID 事件的值为 -1,也就是十六进制的 ffffffff。通过槽事件,可以知道是第一个手指抬起了。

如果最后一个手指也抬起了,会有如下事件

EV_ABS       ABS_MT_TRACKING_ID   ffffffff     
// 同步事件,不属于触摸事件 
EV_SYN       SYN_REPORT           00000000    

通过 ABS_MT_TRACKING_ID 事件可知,手指是抬起了,但是哪个手指抬起了呢?由于抬起的是最后一个手指,因此省略了槽事件。

现在已经了解了 slot 协议,现在让我来看看累加器 MultiTouchMotionAccumulator 是如何收集这个协议上报的数据的

void MultiTouchMotionAccumulator::process(const RawEvent* rawEvent) {
    if (rawEvent->type == EV_ABS) {
        bool newSlot = false;
        if (mUsingSlotsProtocol) {
            // 1. SLOT 协议,使用 ABS_MT_SLOT 事件获取索引
            if (rawEvent->code == ABS_MT_SLOT) {
                mCurrentSlot = rawEvent->value;
                newSlot = true;
            }
        } else if (mCurrentSlot < 0) {
            // 非 SLOT 协议 : 初始上报的事件,默认 slot 为 0
            mCurrentSlot = 0;
        }
        if (mCurrentSlot < 0 || size_t(mCurrentSlot) >= mSlotCount) {
            // ...
        } else {
            // 2. 根据索引,获取 Slot 数组的元素,并填充信息
            Slot* slot = &mSlots[mCurrentSlot];
            if (!mUsingSlotsProtocol) {
                slot->mInUse = true;
            }
            switch (rawEvent->code) {
                case ABS_MT_POSITION_X:
                    slot->mAbsMTPositionX = rawEvent->value;
                    break;
                case ABS_MT_POSITION_Y:
                    slot->mAbsMTPositionY = rawEvent->value;
                    break;
                // ...
                case ABS_MT_TRACKING_ID:
                    if (mUsingSlotsProtocol && rawEvent->value < 0) {
                        // The slot is no longer in use but it retains its previous contents,
                        // which may be reused for subsequent touches.
                        // SLOT 协议: ABS_MT_TRACKING_ID 事件的值小于0,表示当前 slot 不再使用。
                        slot->mInUse = false;
                    } else {
                        // SLOT 协议 : ABS_MT_TRACKING_ID 事件的值为非负值,表示当前 slot 正在使用。
                        slot->mInUse = true;
                        slot->mAbsMTTrackingId = rawEvent->value;
                    }
                    break;
                // ...
            }
        }
    } else if (rawEvent->type == EV_SYN && rawEvent->code == SYN_MT_REPORT) {
        // MultiTouch Sync: The driver has returned all data for *one* of the pointers.
        // 非 SLOT 协议 : EV_SYN + SYN_MT_REPORT 事件,分割手指的触控点信息
        mCurrentSlot += 1;
    }
}

收集 slot 协议上报的数据的过程如下

很简单,就是用 Slot 数组的不同元素,收集不同手指所产生的事件信息。

3. 处理同步事件

根据前面的分析可知,驱动每次上报完触摸事件信息后,都会伴随着一个同步事件。刚才已经收集了触摸事件的信息,现在来看下如何处理同步事件

void TouchInputMapper::process(const RawEvent* rawEvent) {
    mCursorButtonAccumulator.process(rawEvent);
    mCursorScrollAccumulator.process(rawEvent);
    mTouchButtonAccumulator.process(rawEvent);
    // 处理同步事件
    if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {
        sync(rawEvent->when, rawEvent->readTime);
    }
}
void TouchInputMapper::sync(nsecs_t when, nsecs_t readTime) {
    // Push a new state.
    // 添加一个空的元素
    mRawStatesPending.emplace_back();
    // 获取刚刚添加的元素
    RawState& next = mRawStatesPending.back();
    next.clear();
    next.when = when;
    next.readTime = readTime;
    // ...
    // 1. 同步累加器中的数据到 next 中
    // syncTouch() 由子类实现
    syncTouch(when, &next);
    // ...
    // 2. 处理数据
    processRawTouches(false /*timeout*/);
}

处理同步事件的过程如下

3.1 同步数据

void MultiTouchInputMapper::syncTouch(nsecs_t when, RawState* outState) {
    size_t inCount = mMultiTouchMotionAccumulator.getSlotCount();
    size_t outCount = 0;
    BitSet32 newPointerIdBits;
    mHavePointerIds = true;
    for (size_t inIndex = 0; inIndex < inCount; inIndex++) {
        // 从收集器中获取 Slot 数组的元素
        const MultiTouchMotionAccumulator::Slot* inSlot =
                mMultiTouchMotionAccumulator.getSlot(inIndex);
        // 如果 tracking id 为负值,槽就会不再使用
        if (!inSlot->isInUse()) {
            continue;
        }
        if (inSlot->getToolType() == AMOTION_EVENT_TOOL_TYPE_PALM) {
            // ...
        }
        if (outCount >= MAX_POINTERS) {
            break; // too many fingers!
        }
        // 把累加器的Slot数组的数据同步到 RawState::rawPointerData 中
        RawPointerData::Pointer& outPointer = outState->rawPointerData.pointers[outCount];
        outPointer.x = inSlot->getX();
        outPointer.y = inSlot->getY();
        outPointer.pressure = inSlot->getPressure();
        outPointer.touchMajor = inSlot->getTouchMajor();
        outPointer.touchMinor = inSlot->getTouchMinor();
        outPointer.toolMajor = inSlot->getToolMajor();
        outPointer.toolMinor = inSlot->getToolMinor();
        outPointer.orientation = inSlot->getOrientation();
        outPointer.distance = inSlot->getDistance();
        outPointer.tiltX = 0;
        outPointer.tiltY = 0;
        outPointer.toolType = inSlot->getToolType();
        if (outPointer.toolType == AMOTION_EVENT_TOOL_TYPE_UNKNOWN) {
            // ...
        }
        bool isHovering = mTouchButtonAccumulator.getToolType() != AMOTION_EVENT_TOOL_TYPE_MOUSE &&
                (mTouchButtonAccumulator.isHovering() ||
                 (mRawPointerAxes.pressure.valid && inSlot->getPressure() <= 0));
        outPointer.isHovering = isHovering;
        // Assign pointer id using tracking id if available.
        if (mHavePointerIds) {
            int32_t trackingId = inSlot->getTrackingId();
            int32_t id = -1;
            // 把 tracking id 转化为 id
            if (trackingId >= 0) {
                // mPointerIdBits 保存的是手指的所有 id
                // mPointerTrackingIdMap 是建立 id 到 trackingId 的映射
                // 这里就是根据 trackingId 找到 id
                for (BitSet32 idBits(mPointerIdBits); !idBits.isEmpty();) {
                    uint32_t n = idBits.clearFirstMarkedBit();
                    if (mPointerTrackingIdMap[n] == trackingId) {
                        id = n;
                    }
                }
                // id < 0 表示从缓存中,根据 trackingId, 没有获取到 id
                if (id < 0 && !mPointerIdBits.isFull()) {
                    // 从 mPointerIdBits 生成一个 id 
                    id = mPointerIdBits.markFirstUnmarkedBit();
                    // mPointerTrackingIdMap 建立 id 到 trackingId 映射
                    mPointerTrackingIdMap[id] = trackingId;
                }
            }
            // id < 0,表示手指抬起
            if (id < 0) {
                mHavePointerIds = false;
                // 清除对应的数据
                outState->rawPointerData.clearIdBits();
                newPointerIdBits.clear();
            } else { // 有 id
                // 保存id
                outPointer.id = id;
                // 保存 id -> index 映射
                // index 是数组 RawPointerData::pointers 的索引
                outState->rawPointerData.idToIndex[id] = outCount;
                outState->rawPointerData.markIdBit(id, isHovering);
                newPointerIdBits.markBit(id);
            }
        }
        outCount += 1;
    }
    // 保存手指的数量
    outState->rawPointerData.pointerCount = outCount;
    // 保存所有的手指 id
    mPointerIdBits = newPointerIdBits;
    // 对于 SLOT 协议,同步的收尾工作不做任何事
    mMultiTouchMotionAccumulator.finishSync();
}

累加器收集的数据是由驱动直接上报的元数据,这里把元数据同步到 RawState::rawPointerData,它的类型为 RawPointerData ,结构体定义如下

// TouchInputMapper.h
/* Raw data for a collection of pointers including a pointer id mapping table. */
struct RawPointerData {
    struct Pointer {
        uint32_t id; // 手指的 ID
        int32_t x;
        int32_t y;
        // ...
    };
    // 手指的数量
    uint32_t pointerCount;
    // 用 Pointer 数组保存触摸事件的所有信息
    Pointer pointers[MAX_POINTERS];
    // touchingIdBits 保存所有手指的ID
    BitSet32 hoveringIdBits, touchingIdBits, canceledIdBits;
    // 建立手指ID到数组索引的映射
    uint32_t idToIndex[MAX_POINTER_ID + 1];
    // ...
};

介绍下 RawPointerData 的几个成员变量,就可以知道同步后的数据有哪些了

在这里,我要强调几点事

我曾经写了一篇文章 多手指触控,其实也不是很难 ,这篇文章中强调了,在多手指触摸的情况下,只有手指 ID 能唯一代表一个手指,如果想获取某一个手指的触摸事件,那么必须先将 ID 转化为 index,然后使用这个 index 从数组中获取触摸事件的数据。现在,你懂了吗?

3.2 处理同步后的数据

现在数据已经同步到 mRawStatesPending 最后一个元素中,但是这些数据基本上是元数据,是比较晦涩的,接下来看看如何处理这些数据

void TouchInputMapper::processRawTouches(bool timeout) {
    if (mDeviceMode == DeviceMode::DISABLED) {
        // ...
    }
    // 现在开始处理同步过来的数据
    const size_t N = mRawStatesPending.size();
    size_t count;
    for (count = 0; count < N; count++) {
        // 获取数据
        const RawState& next = mRawStatesPending[count];
        // ...
        // 1. mCurrentRawState 保存当前正在处理的元数据
        mCurrentRawState.copyFrom(next);
        if (mCurrentRawState.when < mLastRawState.when) {
            mCurrentRawState.when = mLastRawState.when;
            mCurrentRawState.readTime = mLastRawState.readTime;
        }
        // 2. 加工以及分发
        cookAndDispatch(mCurrentRawState.when, mCurrentRawState.readTime);
    }
    // 成功处理完数据,就从 mRawStatesPending 从擦除
    if (count != 0) {
        mRawStatesPending.erase(mRawStatesPending.begin(), mRawStatesPending.begin() + count);
    }
    if (mExternalStylusDataPending) {
        // ...
    }
}

开始处理元数据之前,首先使用 mCurrentRawState 复制了当前正在处理的数据,后面会使用它进行前后两次的数据对比,生成高级事件,例如 DOWN, MOVE, UP 事件。

然后调用 cookAndDispatch() 对数据进行加工和分发

void TouchInputMapper::cookAndDispatch(nsecs_t when, nsecs_t readTime) {
    // 加工完的数据保存到 mCurrentCookedState
    mCurrentCookedState.clear();
    // ...
    // Consume raw off-screen touches before cooking pointer data.
    // If touches are consumed, subsequent code will not receive any pointer data.
    if (consumeRawTouches(when, readTime, policyFlags)) {
        mCurrentRawState.rawPointerData.clear();
    }
    // 1. 加工事件
    cookPointerData();
    // ...
    // 此时的 device mode 为 DIRECT,表示直接分发
    if (mDeviceMode == DeviceMode::POINTER) {
        // ...
    } else {
        updateTouchSpots();
        if (!mCurrentMotionAborted) {
            dispatchButtonRelease(when, readTime, policyFlags);
            dispatchHoverExit(when, readTime, policyFlags);
            //2. 分发触摸事件
            dispatchTouches(when, readTime, policyFlags);
            dispatchHoverEnterAndMove(when, readTime, policyFlags);
            dispatchButtonPress(when, readTime, policyFlags);
        }
        if (mCurrentCookedState.cookedPointerData.pointerCount == 0) {
            mCurrentMotionAborted = false;
        }
    }
    // ...
    // 保存上一次的元数据和上一次的加工后的数据
    mLastRawState.copyFrom(mCurrentRawState);
    mLastCookedState.copyFrom(mCurrentCookedState);
}

加工和分发事件的过程如下

3.2.1 加工数据

void TouchInputMapper::cookPointerData() {
    uint32_t currentPointerCount = mCurrentRawState.rawPointerData.pointerCount;
    mCurrentCookedState.cookedPointerData.clear();
    mCurrentCookedState.cookedPointerData.pointerCount = currentPointerCount;
    mCurrentCookedState.cookedPointerData.hoveringIdBits =
            mCurrentRawState.rawPointerData.hoveringIdBits;
    mCurrentCookedState.cookedPointerData.touchingIdBits =
            mCurrentRawState.rawPointerData.touchingIdBits;
    mCurrentCookedState.cookedPointerData.canceledIdBits =
            mCurrentRawState.rawPointerData.canceledIdBits;
    if (mCurrentCookedState.cookedPointerData.pointerCount == 0) {
        mCurrentCookedState.buttonState = 0;
    } else {
        mCurrentCookedState.buttonState = mCurrentRawState.buttonState;
    }
    // Walk through the the active pointers and map device coordinates onto
    // surface coordinates and adjust for display orientation.
    for (uint32_t i = 0; i < currentPointerCount; i++) {
        const RawPointerData::Pointer& in = mCurrentRawState.rawPointerData.pointers[i];
        // Size
        // ...
        // Pressure
        // ...
        // Distance
        // ...
        // Coverage
        // ...
        // Adjust X,Y coords for device calibration
        float xTransformed = in.x, yTransformed = in.y;
        mAffineTransform.applyTo(xTransformed, yTransformed);
        // 1. 把输入设备的坐标,转换为显示设备坐标
        // 转换后的坐标,保存到 xTransformed 和 yTransformed 中
        rotateAndScale(xTransformed, yTransformed);
        // Adjust X, Y, and coverage coords for surface orientation.
        // ...
        // Write output coords.
        PointerCoords& out = mCurrentCookedState.cookedPointerData.pointerCoords[i];
        out.clear();
        out.setAxisValue(AMOTION_EVENT_AXIS_X, xTransformed);
        out.setAxisValue(AMOTION_EVENT_AXIS_Y, yTransformed);
        out.setAxisValue(AMOTION_EVENT_AXIS_PRESSURE, pressure);
        out.setAxisValue(AMOTION_EVENT_AXIS_SIZE, size);
        out.setAxisValue(AMOTION_EVENT_AXIS_TOUCH_MAJOR, touchMajor);
        out.setAxisValue(AMOTION_EVENT_AXIS_TOUCH_MINOR, touchMinor);
        out.setAxisValue(AMOTION_EVENT_AXIS_ORIENTATION, orientation);
        out.setAxisValue(AMOTION_EVENT_AXIS_TILT, tilt);
        out.setAxisValue(AMOTION_EVENT_AXIS_DISTANCE, distance);
        if (mCalibration.coverageCalibration == Calibration::CoverageCalibration::BOX) {
            out.setAxisValue(AMOTION_EVENT_AXIS_GENERIC_1, left);
            out.setAxisValue(AMOTION_EVENT_AXIS_GENERIC_2, top);
            out.setAxisValue(AMOTION_EVENT_AXIS_GENERIC_3, right);
            out.setAxisValue(AMOTION_EVENT_AXIS_GENERIC_4, bottom);
        } else {
            out.setAxisValue(AMOTION_EVENT_AXIS_TOOL_MAJOR, toolMajor);
            out.setAxisValue(AMOTION_EVENT_AXIS_TOOL_MINOR, toolMinor);
        }
        // Write output relative fields if applicable.
        uint32_t id = in.id;
        if (mSource == AINPUT_SOURCE_TOUCHPAD &&
            mLastCookedState.cookedPointerData.hasPointerCoordsForId(id)) {
            const PointerCoords& p = mLastCookedState.cookedPointerData.pointerCoordsForId(id);
            float dx = xTransformed - p.getAxisValue(AMOTION_EVENT_AXIS_X);
            float dy = yTransformed - p.getAxisValue(AMOTION_EVENT_AXIS_Y);
            out.setAxisValue(AMOTION_EVENT_AXIS_RELATIVE_X, dx);
            out.setAxisValue(AMOTION_EVENT_AXIS_RELATIVE_Y, dy);
        }
        // Write output properties.
        PointerProperties& properties = mCurrentCookedState.cookedPointerData.pointerProperties[i];
        properties.clear();
        properties.id = id;
        properties.toolType = in.toolType;
        // Write id index and mark id as valid.
        mCurrentCookedState.cookedPointerData.idToIndex[id] = i;
        mCurrentCookedState.cookedPointerData.validIdBits.markBit(id);
    }
}

加工的元数据保存到了 CookedState::cookedPointerData 中,它的类型为 CookedPointerData ,结构体定义如下

struct CookedPointerData {
    uint32_t pointerCount;
    PointerProperties pointerProperties[MAX_POINTERS];
    // 保存坐标数据
    PointerCoords pointerCoords[MAX_POINTERS];
    BitSet32 hoveringIdBits, touchingIdBits, canceledIdBits, validIdBits;
    uint32_t idToIndex[MAX_POINTER_ID + 1];
    // ...
};

一看就明白了什么意思把,就不过多介绍了。

对于手机来的触摸屏来说,触摸事件的加工,最主要的就是把触摸屏的坐标点转换为显示屏的坐标点,如下

// Transform raw coordinate to surface coordinate
void TouchInputMapper::rotateAndScale(float& x, float& y) {
    // Scale to surface coordinate.
    // 1. 根据x,y的缩放比例,计算触摸点在显示设备的缩放坐标
    const float xScaled = float(x - mRawPointerAxes.x.minValue) * mXScale;
    const float yScaled = float(y - mRawPointerAxes.y.minValue) * mYScale;
    const float xScaledMax = float(mRawPointerAxes.x.maxValue - x) * mXScale;
    const float yScaledMax = float(mRawPointerAxes.y.maxValue - y) * mYScale;
    // Rotate to surface coordinate.
    // 0 - no swap and reverse.
    // 90 - swap x/y and reverse y.
    // 180 - reverse x, y.
    // 270 - swap x/y and reverse x.
    // 根据旋转方向计算最终的显示设备的x,y坐标值
    switch (mSurfaceOrientation) {
        case DISPLAY_ORIENTATION_0:
            x = xScaled + mXTranslate;
            y = yScaled + mYTranslate;
            break;
        case DISPLAY_ORIENTATION_90:
            y = xScaledMax - (mRawSurfaceWidth - mSurfaceRight);
            x = yScaled + mYTranslate;
            break;
        case DISPLAY_ORIENTATION_180:
            x = xScaledMax - (mRawSurfaceWidth - mSurfaceRight);
            y = yScaledMax - (mRawSurfaceHeight - mSurfaceBottom);
            break;
        case DISPLAY_ORIENTATION_270:
            y = xScaled + mXTranslate;
            x = yScaledMax - (mRawSurfaceHeight - mSurfaceBottom);
            break;
        default:
            assert(false);
    }
}

这是一道初中的坐标系转换的数学题目,我就不献丑去细致分析了,主要过程如下

3.2.2 分发事件

元数据已经加工完成,现在是时候来分发了

void TouchInputMapper::dispatchTouches(nsecs_t when, nsecs_t readTime, uint32_t policyFlags) {
    BitSet32 currentIdBits = mCurrentCookedState.cookedPointerData.touchingIdBits;
    BitSet32 lastIdBits = mLastCookedState.cookedPointerData.touchingIdBits;
    int32_t metaState = getContext()->getGlobalMetaState();
    int32_t buttonState = mCurrentCookedState.buttonState;
    if (currentIdBits == lastIdBits) {
        if (!currentIdBits.isEmpty()) {
            // No pointer id changes so this is a move event.
            // The listener takes care of batching moves so we don't have to deal with that here.
            // 如果前后两次数据的手指数没有变化,并且当前的手指数不为0,那么此时事件肯定是移动事件,需要分发 AMOTION_EVENT_ACTION_MOVE 事件
            dispatchMotion(when, readTime, policyFlags, mSource, AMOTION_EVENT_ACTION_MOVE, 0, 0,
                           metaState, buttonState, AMOTION_EVENT_EDGE_FLAG_NONE,
                           mCurrentCookedState.cookedPointerData.pointerProperties,
                           mCurrentCookedState.cookedPointerData.pointerCoords,
                           mCurrentCookedState.cookedPointerData.idToIndex, currentIdBits, -1,
                           mOrientedXPrecision, mOrientedYPrecision, mDownTime);
        }
    } else { // 前后两次数据的手指数不相等
        // There may be pointers going up and pointers going down and pointers moving
        // all at the same time.
        BitSet32 upIdBits(lastIdBits.value & ~currentIdBits.value);
        BitSet32 downIdBits(currentIdBits.value & ~lastIdBits.value);
        BitSet32 moveIdBits(lastIdBits.value & currentIdBits.value);
        BitSet32 dispatchedIdBits(lastIdBits.value);
        // Update last coordinates of pointers that have moved so that we observe the new
        // pointer positions at the same time as other pointers that have just gone up.
        // 参数 moveIdBits 表示有移动的手指,这里检测移动的手指,前后两次数据有变化,那么表示需要分发一个移动事件
        bool moveNeeded =
                updateMovedPointers(mCurrentCookedState.cookedPointerData.pointerProperties,
                                    mCurrentCookedState.cookedPointerData.pointerCoords,
                                    mCurrentCookedState.cookedPointerData.idToIndex,
                                    mLastCookedState.cookedPointerData.pointerProperties,
                                    mLastCookedState.cookedPointerData.pointerCoords,
                                    mLastCookedState.cookedPointerData.idToIndex, moveIdBits);
        if (buttonState != mLastCookedState.buttonState) {
            moveNeeded = true;
        }
        // Dispatch pointer up events.
        while (!upIdBits.isEmpty()) {
            uint32_t upId = upIdBits.clearFirstMarkedBit();
            bool isCanceled = mCurrentCookedState.cookedPointerData.canceledIdBits.hasBit(upId);
            if (isCanceled) {
                ALOGI("Canceling pointer %d for the palm event was detected.", upId);
            }
            // 有手指抬起,分发 AMOTION_EVENT_ACTION_POINTER_UP 事件
            dispatchMotion(when, readTime, policyFlags, mSource, AMOTION_EVENT_ACTION_POINTER_UP, 0,
                           isCanceled ? AMOTION_EVENT_FLAG_CANCELED : 0, metaState, buttonState, 0,
                           mLastCookedState.cookedPointerData.pointerProperties,
                           mLastCookedState.cookedPointerData.pointerCoords,
                           mLastCookedState.cookedPointerData.idToIndex, dispatchedIdBits, upId,
                           mOrientedXPrecision, mOrientedYPrecision, mDownTime);
            dispatchedIdBits.clearBit(upId);
            mCurrentCookedState.cookedPointerData.canceledIdBits.clearBit(upId);
        }
        // Dispatch move events if any of the remaining pointers moved from their old locations.
        // Although applications receive new locations as part of individual pointer up
        // events, they do not generally handle them except when presented in a move event.
        // 如果移动的手指前后两次数据有变化,那么分发移动事件
        if (moveNeeded && !moveIdBits.isEmpty()) {
            ALOG_ASSERT(moveIdBits.value == dispatchedIdBits.value);
            dispatchMotion(when, readTime, policyFlags, mSource, AMOTION_EVENT_ACTION_MOVE, 0, 0,
                           metaState, buttonState, 0,
                           mCurrentCookedState.cookedPointerData.pointerProperties,
                           mCurrentCookedState.cookedPointerData.pointerCoords,
                           mCurrentCookedState.cookedPointerData.idToIndex, dispatchedIdBits, -1,
                           mOrientedXPrecision, mOrientedYPrecision, mDownTime);
        }
        // Dispatch pointer down events using the new pointer locations.
        while (!downIdBits.isEmpty()) {
            uint32_t downId = downIdBits.clearFirstMarkedBit();
            dispatchedIdBits.markBit(downId);
            if (dispatchedIdBits.count() == 1) {
                // First pointer is going down.  Set down time.
                mDownTime = when;
            }
            // 有手指按下,分发 AMOTION_EVENT_ACTION_POINTER_DOWN
            dispatchMotion(when, readTime, policyFlags, mSource, AMOTION_EVENT_ACTION_POINTER_DOWN,
                           0, 0, metaState, buttonState, 0,
                           mCurrentCookedState.cookedPointerData.pointerProperties,
                           mCurrentCookedState.cookedPointerData.pointerCoords,
                           mCurrentCookedState.cookedPointerData.idToIndex, dispatchedIdBits,
                           downId, mOrientedXPrecision, mOrientedYPrecision, mDownTime);
        }
    }
}

分发事件的过程,其实就是对比前后两次的数据,生成高级事件 AMOTION_EVENT_ACTION_POINTER_DOWN, AMOTION_EVENT_ACTION_MOVE, AMOTION_EVENT_ACTION_POINTER_UP,然后调用 dispatchMotion() 分发这些高级事件。

void TouchInputMapper::dispatchMotion(nsecs_t when, nsecs_t readTime, uint32_t policyFlags,
                                      uint32_t source, int32_t action, int32_t actionButton,
                                      int32_t flags, int32_t metaState, int32_t buttonState,
                                      int32_t edgeFlags, const PointerProperties* properties,
                                      const PointerCoords* coords, const uint32_t* idToIndex,
                                      BitSet32 idBits, int32_t changedId, float xPrecision,
                                      float yPrecision, nsecs_t downTime) {
    PointerCoords pointerCoords[MAX_POINTERS];
    PointerProperties pointerProperties[MAX_POINTERS];
    uint32_t pointerCount = 0;
    while (!idBits.isEmpty()) {
        uint32_t id = idBits.clearFirstMarkedBit();
        uint32_t index = idToIndex[id];
        pointerProperties[pointerCount].copyFrom(properties[index]);
        pointerCoords[pointerCount].copyFrom(coords[index]);
        // action 添加索引
        // action 中前8位表示手指索引,后8位表示ACTION
        if (changedId >= 0 && id == uint32_t(changedId)) {
            action |= pointerCount << AMOTION_EVENT_ACTION_POINTER_INDEX_SHIFT;
        }
        pointerCount += 1;
    }
    ALOG_ASSERT(pointerCount != 0);
    // 当只有一个手指按下,发送 AMOTION_EVENT_ACTION_DOWN 事件。
    // 但最后一个手指抬起时,发送 AMOTION_EVENT_ACTION_UP 事件。
    if (changedId >= 0 && pointerCount == 1) {
        // Replace initial down and final up action.
        // We can compare the action without masking off the changed pointer index
        // because we know the index is 0.
        if (action == AMOTION_EVENT_ACTION_POINTER_DOWN) {
            action = AMOTION_EVENT_ACTION_DOWN;
        } else if (action == AMOTION_EVENT_ACTION_POINTER_UP) {
            if ((flags & AMOTION_EVENT_FLAG_CANCELED) != 0) {
                action = AMOTION_EVENT_ACTION_CANCEL;
            } else {
                action = AMOTION_EVENT_ACTION_UP;
            }
        } else {
            // Can't happen.
            ALOG_ASSERT(false);
        }
    }
    float xCursorPosition = AMOTION_EVENT_INVALID_CURSOR_POSITION;
    float yCursorPosition = AMOTION_EVENT_INVALID_CURSOR_POSITION;
    if (mDeviceMode == DeviceMode::POINTER) {
        auto [x, y] = getMouseCursorPosition();
        xCursorPosition = x;
        yCursorPosition = y;
    }
    const int32_t displayId = getAssociatedDisplayId().value_or(ADISPLAY_ID_NONE);
    const int32_t deviceId = getDeviceId();
    std::vector<TouchVideoFrame> frames = getDeviceContext().getVideoFrames();
    std::for_each(frames.begin(), frames.end(),
                  [this](TouchVideoFrame& frame) { frame.rotate(this->mSurfaceOrientation); });
    // 把数据包装成 NotifyMotionArgs,并加入到 QueuedInputListener 队列
    NotifyMotionArgs args(getContext()->getNextId(), when, readTime, deviceId, source, displayId,
                          policyFlags, action, actionButton, flags, metaState, buttonState,
                          MotionClassification::NONE, edgeFlags, pointerCount, pointerProperties,
                          pointerCoords, xPrecision, yPrecision, xCursorPosition, yCursorPosition,
                          downTime, std::move(frames));
    getListener()->notifyMotion(&args);
}

可以看到,数据最终被包装成 NotifyMotionArgs 分发到下一环 InputClassifier

但是,在这之前,还对 action 做了如下处理

第2点和第3点,在自定义 View 中处理多手指事件时,是不是很熟悉。

结束

闭上眼睛,想想 InputReader 如何处理触摸事件的。其实就是通过 InputMapper 把触摸屏的坐标点转换为显示屏的坐标点,然后对比前后两次的数据,生成高级事件,然后分发给下一环。so easy !

看我文章的人,是不是大部分是上层的人,前面两篇文章正好是上层应用类型的文章,所以得到大量的点赞反馈。但是须知,经济基础才能决定上层建筑,只有掌握了基础,才能以不变应万变。

关于触摸事件,我也会打算写一篇手势导航的文章,也就是我们经常使用的通过手势进行返回,通过手势回到桌面,这一定是大家最想看到的东西,更多关于InputReader处理触摸事件的资料请关注其它相关文章!

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