touchui: Convert XI2 MT tracking id to slot id for gesture recognizer

views/touchui/touch_factory.cc

Index: views/touchui/touch_factory.cc
diff --git a/views/touchui/touch_factory.cc b/views/touchui/touch_factory.cc
index 09eb704196bd382d2e4911538ba868ca272e3606..30f6c59e1324c7d6681410a1bf4c1606bd35ae8a 100644
--- a/views/touchui/touch_factory.cc
+++ b/views/touchui/touch_factory.cc
@@ -129,10 +129,11 @@ TouchFactory::TouchFactory()
       keep_mouse_cursor_(false),
       cursor_timer_(),
       pointer_device_lookup_(),
+      touch_device_list_(),
 #if defined(USE_XI2_MT)
-      touch_device_list_() {
+      slots_used_(),
+      tracking_id_map_() {
 #else
-      touch_device_list_(),
       slots_used_() {
 #endif
 #if defined(TOUCH_UI)
@@ -319,7 +320,39 @@ bool TouchFactory::IsTouchDevice(unsigned deviceid) const {
       touch_device_lookup_[deviceid] : false;
 }
 
-#if !defined(USE_XI2_MT)
+#if defined(USE_XI2_MT)
+int TouchFactory::GetSlotForTrackingID(uint32 tracking_id) {
+  TrackingIdMap::iterator itr = tracking_id_map_.find(tracking_id);
+  if (itr != tracking_id_map_.end())
+    return itr->second;
+
+  // Finds the lowest available slot and sets up the mapping.
+  int slot = 0;

[Daniel Kurtz, 2011/09/24 01:53:36]

If you store minSlotAvailable as a member variable, you could save yourself some
iterating instead of always starting from 0:

minSlotAvailable starts as 0.
As fingers are added, minSlotAvailable takes the value of the last assigned slot
+ 1 (actually, iterate from assigned slot up until IsSlotUsed() == false).
If a finger is removed, and its slot < minSlotAvailable, then it becomes the new
minSlotAvailable.

[sadrul, 2011/09/24 03:06:31]

This sounds like a good proposal; although I don't expect this to make a lot of
perf improvement.

[ningxin.hu, 2011/09/25 16:35:39]

Good idea! I will follow up the solution. Thanks.

+  while (slot < kMaxTouchPoints) {
+    if (!IsSlotUsed(slot))
+      break;
+    slot++;
+  }
+  if (slot == kMaxTouchPoints) {
+    LOG(ERROR) << "Could not find available slot for touch point";
+    return 0;
+  }
+  SetSlotUsed(slot, true);
+  tracking_id_map_.insert(std::make_pair(tracking_id, slot));
+  return slot;
+}
+
+void TouchFactory::ReleaseSlotForTrackingID(uint32 tracking_id) {
+  TrackingIdMap::iterator itr = tracking_id_map_.find(tracking_id);
+  if (itr != tracking_id_map_.end()) {
+    SetSlotUsed(itr->second, false);
+    tracking_id_map_.erase(itr);
+  } else {
+    NOTREACHED() << "Cannot find slot mapping to tracking ID " << tracking_id;
+  }
+}
+#endif
+
 bool TouchFactory::IsSlotUsed(int slot) const {
   CHECK_LT(slot, kMaxTouchPoints);
   return slots_used_[slot];
@@ -329,7 +362,6 @@ void TouchFactory::SetSlotUsed(int slot, bool used) {
   CHECK_LT(slot, kMaxTouchPoints);
   slots_used_[slot] = used;
 }
-#endif
 
 bool TouchFactory::GrabTouchDevices(Display* display, ::Window window) {
 #if defined(TOUCH_UI)