Preserve multi-touch slot state when resetting input mappers
The existing pattern in InputReader is that when a mapper is reset, all
of its state is cleared and state of the buttons/axes is
queried through EventHub to rebuild the current state of the mapper.
This approach does not work for multi-touch devices, since there is no
way to query the current state of the contacts through the evdev
multi-touch protocol.
Since we cannot fully rebuild the current state of a multi-touch device,
we work around this limitation by never clearing the multi-touch state.
Bug: 248506674
Test: atest inputflinger_tests
Change-Id: Ic59d9fcb4e13fe262c422825c2485185004b719b
diff --git a/services/inputflinger/reader/mapper/MultiTouchInputMapper.cpp b/services/inputflinger/reader/mapper/MultiTouchInputMapper.cpp
index 8f5dc9b..047f068 100644
--- a/services/inputflinger/reader/mapper/MultiTouchInputMapper.cpp
+++ b/services/inputflinger/reader/mapper/MultiTouchInputMapper.cpp
@@ -38,13 +38,9 @@
bool usingSlotsProtocol) {
mUsingSlotsProtocol = usingSlotsProtocol;
mHaveStylus = deviceContext.hasAbsoluteAxis(ABS_MT_TOOL_TYPE);
-
mSlots = std::vector<Slot>(slotCount);
-}
-void MultiTouchMotionAccumulator::reset(InputDeviceContext& deviceContext) {
- // Unfortunately there is no way to read the initial contents of the slots.
- // So when we reset the accumulator, we must assume they are all zeroes.
+ mCurrentSlot = -1;
if (mUsingSlotsProtocol) {
// Query the driver for the current slot index and use it as the initial slot
// before we start reading events from the device. It is possible that the
@@ -56,22 +52,20 @@
// This can cause the touch point to "jump", but at least there will be
// no stuck touches.
int32_t initialSlot;
- status_t status = deviceContext.getAbsoluteAxisValue(ABS_MT_SLOT, &initialSlot);
- if (status) {
- ALOGD("Could not retrieve current multitouch slot index. status=%d", status);
- initialSlot = -1;
+ if (const auto status = deviceContext.getAbsoluteAxisValue(ABS_MT_SLOT, &initialSlot);
+ status == OK) {
+ mCurrentSlot = initialSlot;
+ } else {
+ ALOGD("Could not retrieve current multi-touch slot index. status=%d", status);
}
- clearSlots(initialSlot);
- } else {
- clearSlots(-1);
}
}
-void MultiTouchMotionAccumulator::clearSlots(int32_t initialSlot) {
+void MultiTouchMotionAccumulator::resetSlots() {
for (Slot& slot : mSlots) {
slot.clear();
}
- mCurrentSlot = initialSlot;
+ mCurrentSlot = -1;
}
void MultiTouchMotionAccumulator::process(const RawEvent* rawEvent) {
@@ -159,7 +153,7 @@
void MultiTouchMotionAccumulator::finishSync() {
if (!mUsingSlotsProtocol) {
- clearSlots(-1);
+ resetSlots();
}
}
@@ -198,10 +192,12 @@
MultiTouchInputMapper::~MultiTouchInputMapper() {}
void MultiTouchInputMapper::reset(nsecs_t when) {
- mMultiTouchMotionAccumulator.reset(getDeviceContext());
-
- mPointerIdBits.clear();
-
+ // The evdev multi-touch protocol does not allow userspace applications to query the initial or
+ // current state of the pointers at any time. This means if we clear our accumulated state when
+ // resetting the input mapper, there's no way to rebuild the full initial state of the pointers.
+ // We can only wait for updates to all the pointers and axes. Rather than clearing the state and
+ // rebuilding the state from scratch, we work around this kernel API limitation by never
+ // fully clearing any state specific to the multi-touch protocol.
TouchInputMapper::reset(when);
}