Android12特性“不受信任的触摸事件被屏蔽”其他细节

android12-release
Android 12关于Input触摸事件的行为变更这篇介绍了input实际的拦截findTouchedWindowTargetsLocked

“不受信任的触摸事件被屏蔽”相关属性

mBlockUntrustedTouchesMode

三种属性值：DISABLED不拦截；PERMISSIVE拦截判断最后没拦截；BLOCK拦截
frameworks\base\core\java\android\hardware\input\InputManager.java
frameworks/native/libs/input/android/os/BlockUntrustedTouchesMode.aidl

    /** @hide */public static final int[] BLOCK_UNTRUSTED_TOUCHES_MODES = {BlockUntrustedTouchesMode.DISABLED,BlockUntrustedTouchesMode.PERMISSIVE,BlockUntrustedTouchesMode.BLOCK};

block_untrusted_touches设置/获取:Settings.Global.BLOCK_UNTRUSTED_TOUCHES_MODE改变 -- InputManagerService.java -- JNI -- InputDispatcher.cpp

adb shell settings get global block_untrusted_touches
adb shell settings put global block_untrusted_touches 0
单个应用设置
adb shell am compat disable BLOCK_UNTRUSTED_TOUCHES com.example.app
adb shell am compat reset BLOCK_UNTRUSTED_TOUCHES com.example.app

frameworks/base/cmds/am/src/com/android/commands/am/Am.java
frameworks/base/services/core/java/com/android/server/am/ActivityManagerShellCommand.java
frameworks/base/services/core/java/com/android/server/compat/PlatformCompat.java
frameworks/base/services/core/java/com/android/server/wm/InputMonitor.java
frameworks/base/services/core/java/com/android/server/wm/WindowState.java
frameworks/base/core/java/android/app/compat/CompatChanges.java
frameworks/base/core/java/android/app/compat/ChangeIdStateCache.java
frameworks/base/core/java/android/app/compat/ChangeIdStateQuery.java

TouchOcclusionInfo

frameworks/native/services/inputflinger/dispatcher/InputDispatcher.h

struct TouchOcclusionInfo {bool hasBlockingOcclusion;float obscuringOpacity;std::string obscuringPackage;int32_t obscuringUid;std::vector<std::string> debugInfo;
};

computeTouchOcclusionInfoLocked赋值
frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp

hasBlockingOcclusion 界面InputWindowInfo属性touchOcclusionMode==BLOCK_UNTRUSTED时为true

obscuringOpacity 界面InputWindowInfo属性touchOcclusionMode==USE_OPACITY时计算透明度

obscuringUid、obscuringPackage 界面InputWindowInfo属性touchOcclusionMode!=ALLOW时会赋值

debugInfo 当DEBUG_TOUCH_OCCLUSION打开时赋值界面信息InputWindowInfo

canBeObscuredBy(windowHandle, otherHandle)当InputWindowHandle可见visible、不信任trustedOverlay等时赋值，否则，返回TouchOcclusionInfo默认值

InputDispatcher::TouchOcclusionInfo InputDispatcher::computeTouchOcclusionInfoLocked(const sp<InputWindowHandle>& windowHandle, int32_t x, int32_t y) const {const InputWindowInfo* windowInfo = windowHandle->getInfo();int32_t displayId = windowInfo->displayId;const std::vector<sp<InputWindowHandle>>& windowHandles = getWindowHandlesLocked(displayId);TouchOcclusionInfo info;info.hasBlockingOcclusion = false;info.obscuringOpacity = 0;info.obscuringUid = -1;std::map<int32_t, float> opacityByUid;for (const sp<InputWindowHandle>& otherHandle : windowHandles) {if (windowHandle == otherHandle) {break; // All future windows are below us. Exit early.}const InputWindowInfo* otherInfo = otherHandle->getInfo();if (canBeObscuredBy(windowHandle, otherHandle) && otherInfo->frameContainsPoint(x, y) &&!haveSameApplicationToken(windowInfo, otherInfo)) {if (DEBUG_TOUCH_OCCLUSION) {info.debugInfo.push_back(dumpWindowForTouchOcclusion(otherInfo, /* isTouchedWindow */ false));}// canBeObscuredBy() has returned true above, which means this window is untrusted, so// we perform the checks below to see if the touch can be propagated or not based on the// window's touch occlusion modeif (otherInfo->touchOcclusionMode == TouchOcclusionMode::BLOCK_UNTRUSTED) {info.hasBlockingOcclusion = true;info.obscuringUid = otherInfo->ownerUid;info.obscuringPackage = otherInfo->packageName;break;}if (otherInfo->touchOcclusionMode == TouchOcclusionMode::USE_OPACITY) {uint32_t uid = otherInfo->ownerUid;float opacity =(opacityByUid.find(uid) == opacityByUid.end()) ? 0 : opacityByUid[uid];// Given windows A and B:// opacity(A, B) = 1 - [1 - opacity(A)] * [1 - opacity(B)]opacity = 1 - (1 - opacity) * (1 - otherInfo->alpha);opacityByUid[uid] = opacity;if (opacity > info.obscuringOpacity) {info.obscuringOpacity = opacity;info.obscuringUid = uid;info.obscuringPackage = otherInfo->packageName;}}}}if (DEBUG_TOUCH_OCCLUSION) {info.debugInfo.push_back(dumpWindowForTouchOcclusion(windowInfo, /* isTouchedWindow */ true));}return info;
}

!isTouchTrustedLocked根据TouchOcclusionInfo判断是否拦截

hasBlockingOcclusion 界面InputWindowInfo属性touchOcclusionMode==BLOCK_UNTRUSTED时拦截

模糊不透明度obscuringOpacity大于mMaximumObscuringOpacityForTouch时拦截(mMaximumObscuringOpacityForTouch为Settings.Global.getUriFor(Settings.Global.MAXIMUM_OBSCURING_OPACITY_FOR_TOUCH)属性值，默认0.8f)

bool InputDispatcher::isTouchTrustedLocked(const TouchOcclusionInfo& occlusionInfo) const {if (occlusionInfo.hasBlockingOcclusion) {ALOGW("Untrusted touch due to occlusion by %s/%d", occlusionInfo.obscuringPackage.c_str(),occlusionInfo.obscuringUid);return false;}if (occlusionInfo.obscuringOpacity > mMaximumObscuringOpacityForTouch) {ALOGW("Untrusted touch due to occlusion by %s/%d (obscuring opacity = ""%.2f, maximum allowed = %.2f)",occlusionInfo.obscuringPackage.c_str(), occlusionInfo.obscuringUid,occlusionInfo.obscuringOpacity, mMaximumObscuringOpacityForTouch);return false;}return true;
}

什么情况不拦截

回顾上边属性，并查看Android 12关于Input触摸事件的行为变更图代码：

// Drop events that can't be trusted due to occlusion
if (newTouchedWindowHandle != nullptr &&mBlockUntrustedTouchesMode != BlockUntrustedTouchesMode::DISABLED) {TouchOcclusionInfo occlusionInfo =computeTouchOcclusionInfoLocked(newTouchedWindowHandle, x, y);if (!isTouchTrustedLocked(occlusionInfo)) {if (DEBUG_TOUCH_OCCLUSION) {ALOGD("Stack of obscuring windows during untrusted touch (%d, %d):", x, y);for (const auto& log : occlusionInfo.debugInfo) {ALOGD("%s", log.c_str());}}onUntrustedTouchLocked(occlusionInfo.obscuringPackage);if (mBlockUntrustedTouchesMode == BlockUntrustedTouchesMode::BLOCK) {ALOGW("Dropping untrusted touch event due to %s/%d",occlusionInfo.obscuringPackage.c_str(), occlusionInfo.obscuringUid);newTouchedWindowHandle = nullptr;}}
}

BlockUntrustedTouchesMode为DISABLED、PERMISSIVE不拦截

当窗口InputWindowHandle可见visible、信任trustedOverlay时TouchOcclusionInfo默认!isTouchTrustedLocked为false，不拦截

当窗口InputWindowInfo属性touchOcclusionMode=ALLOW时TouchOcclusionInfo默认!isTouchTrustedLocked为false，不拦截

设置adb shell am compat disable BLOCK_UNTRUSTED_TOUCHES com.example.app时com.example.app该应用不拦截(实质同第3种touchOcclusionMode=ALLOW一样)

拦截通知弹框

onUntrustedTouchLocked(occlusionInfo.obscuringPackage) -- JNI -- InputManagerService.java

UNTRUSTED_TOUCHES_TOAST默认关闭Toast弹框

PACKAGE_BLOCKLIST_FOR_UNTRUSTED_TOUCHES_TOAST 配置不弹框
private static final String[] PACKAGE_BLOCKLIST_FOR_UNTRUSTED_TOUCHES_TOAST = {"com.snapchat.android" // b/173297887
};