Fix resampling for multiple pointers

If more than one pointer is present and identical coordinates are
encountered for any pointer, the lastResample value will not be
invalidated (by clearing its bits). As a result, the same lastResample
value will be used to subsequently rewriteMessage any time in the
future. This can cause significant jumps in the pointer coordinates, and
is a bug. To further clarify, this bug has only to do with resampling
and nothing to do with both pointers having the same X or Y value.

This CL makes this logic to be per-pointer. As soon as non-identical
value is encountered and the timing conditions are such that the
resampled value is not needed to be used, the lastResample bit for that
pointer will be cleared, meaning that the value in lastResample for this
pointer is stale. This value will no longer be used anywhere.

When performing resampling, allow the process to happen on a per-pointer
basis. If one of the pointers has encountered events with identical
coordinates, then use the previously resampled value (do not resample
again), if that value is still valid (see above). Otherwise, the normal
resampling path will be taken. On the other pointers that do not have
identical coordinates, go through the normal path as well.

Bug: 68840121
Test: recorded a repro event with inputstudio and replayed it while
observing the screen. Saw that the coordinates jump before the fix,
and do not jump with the fix.

Change-Id: If43c323759de8f0184b76221d1ae599a75349ce9
Merged-In: If43c323759de8f0184b76221d1ae599a75349ce9

1 files changed, 36 insertions, 23 deletions

diff --git a/libs/input/InputTransport.cpp b/libs/input/InputTransport.cpp
index 9abd04ca04..905d336bfe 100644
--- a/libs/input/InputTransport.cpp
+++ b/libs/input/InputTransport.cpp
@@ -614,10 +614,7 @@ void InputConsumer::updateTouchState(InputMessage& msg) {
         if (index >= 0) {
             TouchState& touchState = mTouchStates.editItemAt(index);
             touchState.addHistory(msg);
-            bool messageRewritten = rewriteMessage(touchState, msg);
-            if (!messageRewritten) {
-                touchState.lastResample.idBits.clear();
-            }
+            rewriteMessage(touchState, msg);
         }
         break;
     }
@@ -645,7 +642,7 @@ void InputConsumer::updateTouchState(InputMessage& msg) {
     case AMOTION_EVENT_ACTION_SCROLL: {
         ssize_t index = findTouchState(deviceId, source);
         if (index >= 0) {
-            const TouchState& touchState = mTouchStates.itemAt(index);
+            TouchState& touchState = mTouchStates.editItemAt(index);
             rewriteMessage(touchState, msg);
         }
         break;
@@ -655,7 +652,7 @@ void InputConsumer::updateTouchState(InputMessage& msg) {
     case AMOTION_EVENT_ACTION_CANCEL: {
         ssize_t index = findTouchState(deviceId, source);
         if (index >= 0) {
-            const TouchState& touchState = mTouchStates.itemAt(index);
+            TouchState& touchState = mTouchStates.editItemAt(index);
             rewriteMessage(touchState, msg);
             mTouchStates.removeAt(index);
         }
@@ -664,28 +661,38 @@ void InputConsumer::updateTouchState(InputMessage& msg) {
     }
 }
 
-bool InputConsumer::rewriteMessage(const TouchState& state, InputMessage& msg) {
-    bool messageRewritten = false;
+/**
+ * Replace the coordinates in msg with the coordinates in lastResample, if necessary.
+ *
+ * If lastResample is no longer valid for a specific pointer (i.e. the lastResample time
+ * is in the past relative to msg and the past two events do not contain identical coordinates),
+ * then invalidate the lastResample data for that pointer.
+ * If the two past events have identical coordinates, then lastResample data for that pointer will
+ * remain valid, and will be used to replace these coordinates. Thus, if a certain coordinate x0 is
+ * resampled to the new value x1, then x1 will always be used to replace x0 until some new value
+ * not equal to x0 is received.
+ */
+void InputConsumer::rewriteMessage(TouchState& state, InputMessage& msg) {
     nsecs_t eventTime = msg.body.motion.eventTime;
     for (uint32_t i = 0; i < msg.body.motion.pointerCount; i++) {
         uint32_t id = msg.body.motion.pointers[i].properties.id;
         if (state.lastResample.idBits.hasBit(id)) {
-            PointerCoords& msgCoords = msg.body.motion.pointers[i].coords;
-            const PointerCoords& resampleCoords = state.lastResample.getPointerById(id);
             if (eventTime < state.lastResample.eventTime ||
                     state.recentCoordinatesAreIdentical(id)) {
-                msgCoords.setAxisValue(AMOTION_EVENT_AXIS_X, resampleCoords.getX());
-                msgCoords.setAxisValue(AMOTION_EVENT_AXIS_Y, resampleCoords.getY());
+                PointerCoords& msgCoords = msg.body.motion.pointers[i].coords;
+                const PointerCoords& resampleCoords = state.lastResample.getPointerById(id);
 #if DEBUG_RESAMPLING
                 ALOGD("[%d] - rewrite (%0.3f, %0.3f), old (%0.3f, %0.3f)", id,
                         resampleCoords.getX(), resampleCoords.getY(),
                         msgCoords.getX(), msgCoords.getY());
 #endif
-                messageRewritten = true;
+                msgCoords.setAxisValue(AMOTION_EVENT_AXIS_X, resampleCoords.getX());
+                msgCoords.setAxisValue(AMOTION_EVENT_AXIS_Y, resampleCoords.getY());
+            } else {
+                state.lastResample.idBits.clearBit(id);
             }
         }
     }
-    return messageRewritten;
 }
 
 void InputConsumer::resampleTouchState(nsecs_t sampleTime, MotionEvent* event,
@@ -713,7 +720,6 @@ void InputConsumer::resampleTouchState(nsecs_t sampleTime, MotionEvent* event,
     }
 
     // Ensure that the current sample has all of the pointers that need to be reported.
-    // Also ensure that the past two "real" touch events do not contain duplicate coordinates
     const History* current = touchState.getHistory(0);
     size_t pointerCount = event->getPointerCount();
     for (size_t i = 0; i < pointerCount; i++) {
@@ -724,12 +730,6 @@ void InputConsumer::resampleTouchState(nsecs_t sampleTime, MotionEvent* event,
 #endif
             return;
         }
-        if (touchState.recentCoordinatesAreIdentical(id)) {
-#if DEBUG_RESAMPLING
-            ALOGD("Not resampled, past two historical events have duplicate coordinates");
-#endif
-            return;
-        }
     }
 
     // Find the data to use for resampling.
@@ -783,18 +783,32 @@ void InputConsumer::resampleTouchState(nsecs_t sampleTime, MotionEvent* event,
     }
 
     // Resample touch coordinates.
+    History oldLastResample;
+    oldLastResample.initializeFrom(touchState.lastResample);
     touchState.lastResample.eventTime = sampleTime;
     touchState.lastResample.idBits.clear();
     for (size_t i = 0; i < pointerCount; i++) {
         uint32_t id = event->getPointerId(i);
         touchState.lastResample.idToIndex[id] = i;
         touchState.lastResample.idBits.markBit(id);
+        if (oldLastResample.hasPointerId(id) && touchState.recentCoordinatesAreIdentical(id)) {
+            // We maintain the previously resampled value for this pointer (stored in
+            // oldLastResample) when the coordinates for this pointer haven't changed since then.
+            // This way we don't introduce artificial jitter when pointers haven't actually moved.
+
+            // We know here that the coordinates for the pointer haven't changed because we
+            // would've cleared the resampled bit in rewriteMessage if they had. We can't modify
+            // lastResample in place becasue the mapping from pointer ID to index may have changed.
+            touchState.lastResample.pointers[i].copyFrom(oldLastResample.getPointerById(id));
+            continue;
+        }
+
         PointerCoords& resampledCoords = touchState.lastResample.pointers[i];
         const PointerCoords& currentCoords = current->getPointerById(id);
+        resampledCoords.copyFrom(currentCoords);
         if (other->idBits.hasBit(id)
                 && shouldResampleTool(event->getToolType(i))) {
             const PointerCoords& otherCoords = other->getPointerById(id);
-            resampledCoords.copyFrom(currentCoords);
             resampledCoords.setAxisValue(AMOTION_EVENT_AXIS_X,
                     lerp(currentCoords.getX(), otherCoords.getX(), alpha));
             resampledCoords.setAxisValue(AMOTION_EVENT_AXIS_Y,
@@ -808,7 +822,6 @@ void InputConsumer::resampleTouchState(nsecs_t sampleTime, MotionEvent* event,
                     alpha);
 #endif
         } else {
-            resampledCoords.copyFrom(currentCoords);
 #if DEBUG_RESAMPLING
             ALOGD("[%d] - out (%0.3f, %0.3f), cur (%0.3f, %0.3f)",
                     id, resampledCoords.getX(), resampledCoords.getY(),