diff --git a/java/src/com/android/inputmethod/keyboard/PointerTracker.java b/java/src/com/android/inputmethod/keyboard/PointerTracker.java
index 8f43dce..3fee6c6 100644
--- a/java/src/com/android/inputmethod/keyboard/PointerTracker.java
+++ b/java/src/com/android/inputmethod/keyboard/PointerTracker.java
@@ -24,10 +24,10 @@
 
 import com.android.inputmethod.keyboard.internal.BogusMoveEventDetector;
 import com.android.inputmethod.keyboard.internal.GestureEnabler;
-import com.android.inputmethod.keyboard.internal.GestureStroke;
-import com.android.inputmethod.keyboard.internal.GestureStrokeParams;
-import com.android.inputmethod.keyboard.internal.GestureStrokePreviewParams;
-import com.android.inputmethod.keyboard.internal.GestureStrokeWithPreviewPoints;
+import com.android.inputmethod.keyboard.internal.GestureStrokeDrawingParams;
+import com.android.inputmethod.keyboard.internal.GestureStrokeDrawingPoints;
+import com.android.inputmethod.keyboard.internal.GestureStrokeRecognitionParams;
+import com.android.inputmethod.keyboard.internal.GestureStrokeRecognitionPoints;
 import com.android.inputmethod.keyboard.internal.PointerTrackerQueue;
 import com.android.inputmethod.keyboard.internal.TypingTimeRecorder;
 import com.android.inputmethod.latin.Constants;
@@ -135,8 +135,8 @@
 
     // Parameters for pointer handling.
     private static PointerTrackerParams sParams;
-    private static GestureStrokeParams sGestureStrokeParams;
-    private static GestureStrokePreviewParams sGesturePreviewParams;
+    private static GestureStrokeRecognitionParams sGestureStrokeRecognitionParams;
+    private static GestureStrokeDrawingParams sGestureStrokeDrawingParams;
     private static boolean sNeedsPhantomSuddenMoveEventHack;
     // Move this threshold to resource.
     // TODO: Device specific parameter would be better for device specific hack?
@@ -163,7 +163,7 @@
     private static long sGestureFirstDownTime;
     private static TypingTimeRecorder sTypingTimeRecorder;
     private static final InputPointers sAggregatedPointers = new InputPointers(
-            GestureStroke.DEFAULT_CAPACITY);
+            GestureStrokeRecognitionPoints.DEFAULT_CAPACITY);
     private static int sLastRecognitionPointSize = 0; // synchronized using sAggregatedPointers
     private static long sLastRecognitionTime = 0; // synchronized using sAggregatedPointers
 
@@ -203,16 +203,16 @@
     // true if dragging finger is allowed.
     private boolean mIsAllowedDraggingFinger;
 
-    private final GestureStrokeWithPreviewPoints mGestureStrokeWithPreviewPoints;
+    private final GestureStrokeDrawingPoints mGestureStrokeDrawingPoints;
 
     // TODO: Add PointerTrackerFactory singleton and move some class static methods into it.
     public static void init(final TypedArray mainKeyboardViewAttr, final TimerProxy timerProxy,
             final DrawingProxy drawingProxy) {
         sParams = new PointerTrackerParams(mainKeyboardViewAttr);
-        sGestureStrokeParams = new GestureStrokeParams(mainKeyboardViewAttr);
-        sGesturePreviewParams = new GestureStrokePreviewParams(mainKeyboardViewAttr);
+        sGestureStrokeRecognitionParams = new GestureStrokeRecognitionParams(mainKeyboardViewAttr);
+        sGestureStrokeDrawingParams = new GestureStrokeDrawingParams(mainKeyboardViewAttr);
         sTypingTimeRecorder = new TypingTimeRecorder(
-                sGestureStrokeParams.mStaticTimeThresholdAfterFastTyping,
+                sGestureStrokeRecognitionParams.mStaticTimeThresholdAfterFastTyping,
                 sParams.mSuppressKeyPreviewAfterBatchInputDuration);
 
         final Resources res = mainKeyboardViewAttr.getResources();
@@ -286,8 +286,8 @@
 
     private PointerTracker(final int id) {
         mPointerId = id;
-        mGestureStrokeWithPreviewPoints = new GestureStrokeWithPreviewPoints(
-                id, sGestureStrokeParams, sGesturePreviewParams);
+        mGestureStrokeDrawingPoints = new GestureStrokeDrawingPoints(
+                id, sGestureStrokeRecognitionParams, sGestureStrokeDrawingParams);
     }
 
     // Returns true if keyboard has been changed by this callback.
@@ -408,7 +408,7 @@
         mKeyboardLayoutHasBeenChanged = true;
         final int keyWidth = mKeyboard.mMostCommonKeyWidth;
         final int keyHeight = mKeyboard.mMostCommonKeyHeight;
-        mGestureStrokeWithPreviewPoints.setKeyboardGeometry(keyWidth, mKeyboard.mOccupiedHeight);
+        mGestureStrokeDrawingPoints.setKeyboardGeometry(keyWidth, mKeyboard.mOccupiedHeight);
         final Key newKey = mKeyDetector.detectHitKey(mKeyX, mKeyY);
         if (newKey != mCurrentKey) {
             if (sDrawingProxy != null) {
@@ -523,8 +523,8 @@
         sDrawingProxy.invalidateKey(key);
     }
 
-    public GestureStrokeWithPreviewPoints getGestureStrokeWithPreviewPoints() {
-        return mGestureStrokeWithPreviewPoints;
+    public GestureStrokeDrawingPoints getGestureStrokeDrawingPoints() {
+        return mGestureStrokeDrawingPoints;
     }
 
     public void getLastCoordinates(final int[] outCoords) {
@@ -581,7 +581,7 @@
      * @return true if the batch input has started successfully.
      */
     private boolean mayStartBatchInput() {
-        if (!mGestureStrokeWithPreviewPoints.isStartOfAGesture()) {
+        if (!mGestureStrokeDrawingPoints.isStartOfAGesture()) {
             return false;
         }
         if (DEBUG_LISTENER) {
@@ -609,13 +609,13 @@
 
     public void updateBatchInputByTimer(final long syntheticMoveEventTime) {
         final int gestureTime = (int)(syntheticMoveEventTime - sGestureFirstDownTime);
-        mGestureStrokeWithPreviewPoints.duplicateLastPointWith(gestureTime);
+        mGestureStrokeDrawingPoints.duplicateLastPointWith(gestureTime);
         updateBatchInput(syntheticMoveEventTime);
     }
 
     private void updateBatchInput(final long moveEventTime) {
         synchronized (sAggregatedPointers) {
-            final GestureStroke stroke = mGestureStrokeWithPreviewPoints;
+            final GestureStrokeRecognitionPoints stroke = mGestureStrokeDrawingPoints;
             stroke.appendIncrementalBatchPoints(sAggregatedPointers);
             final int size = sAggregatedPointers.getPointerSize();
             if (size > sLastRecognitionPointSize
@@ -642,7 +642,7 @@
     private boolean mayEndBatchInput(final long upEventTime) {
         boolean hasEndBatchInputSuccessfully = false;
         synchronized (sAggregatedPointers) {
-            mGestureStrokeWithPreviewPoints.appendAllBatchPoints(sAggregatedPointers);
+            mGestureStrokeDrawingPoints.appendAllBatchPoints(sAggregatedPointers);
             if (getActivePointerTrackerCount() == 1) {
                 hasEndBatchInputSuccessfully = true;
                 sTypingTimeRecorder.onEndBatchInput(upEventTime);
@@ -754,7 +754,7 @@
             if (getActivePointerTrackerCount() == 1) {
                 sGestureFirstDownTime = eventTime;
             }
-            mGestureStrokeWithPreviewPoints.onDownEvent(x, y, eventTime, sGestureFirstDownTime,
+            mGestureStrokeDrawingPoints.onDownEvent(x, y, eventTime, sGestureFirstDownTime,
                     sTypingTimeRecorder.getLastLetterTypingTime());
         }
     }
@@ -814,11 +814,11 @@
         if (!mIsDetectingGesture) {
             return;
         }
-        final int beforeLength = mGestureStrokeWithPreviewPoints.getLength();
+        final int beforeLength = mGestureStrokeDrawingPoints.getLength();
         final int gestureTime = (int)(eventTime - sGestureFirstDownTime);
-        final boolean onValidArea = mGestureStrokeWithPreviewPoints.addPointOnKeyboard(
+        final boolean onValidArea = mGestureStrokeDrawingPoints.addPointOnKeyboard(
                 x, y, gestureTime, isMajorEvent);
-        if (mGestureStrokeWithPreviewPoints.getLength() > beforeLength) {
+        if (mGestureStrokeDrawingPoints.getLength() > beforeLength) {
             sTimerProxy.startUpdateBatchInputTimer(this);
         }
         // If the move event goes out from valid batch input area, cancel batch input.
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokePreviewParams.java b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeDrawingParams.java
similarity index 81%
rename from java/src/com/android/inputmethod/keyboard/internal/GestureStrokePreviewParams.java
rename to java/src/com/android/inputmethod/keyboard/internal/GestureStrokeDrawingParams.java
index 6695476..478639d 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokePreviewParams.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeDrawingParams.java
@@ -20,7 +20,15 @@
 
 import com.android.inputmethod.latin.R;
 
-public final class GestureStrokePreviewParams {
+/**
+ * This class holds parameters to control how a gesture stroke is sampled and drawn on the screen.
+ *
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailMinSamplingDistance
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailMaxInterpolationAngularThreshold
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailMaxInterpolationDistanceThreshold
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailMaxInterpolationSegments
+ */
+public final class GestureStrokeDrawingParams {
     public final double mMinSamplingDistance; // in pixel
     public final double mMaxInterpolationAngularThreshold; // in radian
     public final double mMaxInterpolationDistanceThreshold; // in pixel
@@ -31,7 +39,7 @@
     private static final float DEFAULT_MAX_INTERPOLATION_DISTANCE_THRESHOLD = 0.0f; // dp
     private static final int DEFAULT_MAX_INTERPOLATION_SEGMENTS = 4;
 
-    public GestureStrokePreviewParams(final TypedArray mainKeyboardViewAttr) {
+    public GestureStrokeDrawingParams(final TypedArray mainKeyboardViewAttr) {
         mMinSamplingDistance = mainKeyboardViewAttr.getDimension(
                 R.styleable.MainKeyboardView_gestureTrailMinSamplingDistance,
                 DEFAULT_MIN_SAMPLING_DISTANCE);
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeDrawingPoints.java
similarity index 82%
rename from java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java
rename to java/src/com/android/inputmethod/keyboard/internal/GestureStrokeDrawingPoints.java
index 22407d8..0c09cbc 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeDrawingPoints.java
@@ -18,14 +18,20 @@
 
 import com.android.inputmethod.latin.utils.ResizableIntArray;
 
-public final class GestureStrokeWithPreviewPoints extends GestureStroke {
+/**
+ * This class holds drawing points to represent a gesture stroke on the screen.
+ * TODO: Currently this class extends {@link GestureStrokeRecognitionPoints} that holds recognition
+ * points of a gesture stroke. This class should be independent from
+ * {@link GestureStrokeRecognitionPoints}.
+ */
+public final class GestureStrokeDrawingPoints extends GestureStrokeRecognitionPoints {
     public static final int PREVIEW_CAPACITY = 256;
 
     private final ResizableIntArray mPreviewEventTimes = new ResizableIntArray(PREVIEW_CAPACITY);
     private final ResizableIntArray mPreviewXCoordinates = new ResizableIntArray(PREVIEW_CAPACITY);
     private final ResizableIntArray mPreviewYCoordinates = new ResizableIntArray(PREVIEW_CAPACITY);
 
-    private final GestureStrokePreviewParams mPreviewParams;
+    private final GestureStrokeDrawingParams mDrawingParams;
 
     private int mStrokeId;
     private int mLastPreviewSize;
@@ -36,11 +42,11 @@
     private int mLastY;
     private double mDistanceFromLastSample;
 
-    public GestureStrokeWithPreviewPoints(final int pointerId,
-            final GestureStrokeParams strokeParams,
-            final GestureStrokePreviewParams previewParams) {
-        super(pointerId, strokeParams);
-        mPreviewParams = previewParams;
+    public GestureStrokeDrawingPoints(final int pointerId,
+            final GestureStrokeRecognitionParams recognitionParams,
+            final GestureStrokeDrawingParams drawingParams) {
+        super(pointerId, recognitionParams);
+        mDrawingParams = drawingParams;
     }
 
     @Override
@@ -63,7 +69,7 @@
         mLastX = x;
         mLastY = y;
         final boolean isDownEvent = (mPreviewEventTimes.getLength() == 0);
-        if (mDistanceFromLastSample >= mPreviewParams.mMinSamplingDistance || isDownEvent) {
+        if (mDistanceFromLastSample >= mDrawingParams.mMinSamplingDistance || isDownEvent) {
             mDistanceFromLastSample = 0.0d;
             return true;
         }
@@ -89,7 +95,7 @@
      * @param xCoords the x-coordinates array of gesture trail to be drawn.
      * @param yCoords the y-coordinates array of gesture trail to be drawn.
      * @param types the point types array of gesture trail. This is valid only when
-     * {@link GestureTrail#DEBUG_SHOW_POINTS} is true.
+     * {@link GestureTrailDrawingPoints#DEBUG_SHOW_POINTS} is true.
      */
     public void appendPreviewStroke(final ResizableIntArray eventTimes,
             final ResizableIntArray xCoords, final ResizableIntArray yCoords,
@@ -101,8 +107,8 @@
         eventTimes.append(mPreviewEventTimes, mLastPreviewSize, length);
         xCoords.append(mPreviewXCoordinates, mLastPreviewSize, length);
         yCoords.append(mPreviewYCoordinates, mLastPreviewSize, length);
-        if (GestureTrail.DEBUG_SHOW_POINTS) {
-            types.fill(GestureTrail.POINT_TYPE_SAMPLED, types.getLength(), length);
+        if (GestureTrailDrawingPoints.DEBUG_SHOW_POINTS) {
+            types.fill(GestureTrailDrawingPoints.POINT_TYPE_SAMPLED, types.getLength(), length);
         }
         mLastPreviewSize = mPreviewEventTimes.getLength();
     }
@@ -119,7 +125,7 @@
      * @param xCoords the x-coordinates array of gesture trail to be drawn.
      * @param yCoords the y-coordinates array of gesture trail to be drawn.
      * @param types the point types array of gesture trail. This is valid only when
-     * {@link GestureTrail#DEBUG_SHOW_POINTS} is true.
+     * {@link GestureTrailDrawingPoints#DEBUG_SHOW_POINTS} is true.
      * @return the start index of the last interpolated segment of input arrays.
      */
     public int interpolateStrokeAndReturnStartIndexOfLastSegment(final int lastInterpolatedIndex,
@@ -145,12 +151,12 @@
             final double m2 = Math.atan2(mInterpolator.mSlope2Y, mInterpolator.mSlope2X);
             final double deltaAngle = Math.abs(angularDiff(m2, m1));
             final int segmentsByAngle = (int)Math.ceil(
-                    deltaAngle / mPreviewParams.mMaxInterpolationAngularThreshold);
+                    deltaAngle / mDrawingParams.mMaxInterpolationAngularThreshold);
             final double deltaDistance = Math.hypot(mInterpolator.mP1X - mInterpolator.mP2X,
                     mInterpolator.mP1Y - mInterpolator.mP2Y);
             final int segmentsByDistance = (int)Math.ceil(deltaDistance
-                    / mPreviewParams.mMaxInterpolationDistanceThreshold);
-            final int segments = Math.min(mPreviewParams.mMaxInterpolationSegments,
+                    / mDrawingParams.mMaxInterpolationDistanceThreshold);
+            final int segments = Math.min(mDrawingParams.mMaxInterpolationSegments,
                     Math.max(segmentsByAngle, segmentsByDistance));
             final int t1 = eventTimes.get(d1);
             final int dt = pt[p2] - pt[p1];
@@ -161,16 +167,16 @@
                 eventTimes.add(d1, (int)(dt * t) + t1);
                 xCoords.add(d1, (int)mInterpolator.mInterpolatedX);
                 yCoords.add(d1, (int)mInterpolator.mInterpolatedY);
-                if (GestureTrail.DEBUG_SHOW_POINTS) {
-                    types.add(d1, GestureTrail.POINT_TYPE_INTERPOLATED);
+                if (GestureTrailDrawingPoints.DEBUG_SHOW_POINTS) {
+                    types.add(d1, GestureTrailDrawingPoints.POINT_TYPE_INTERPOLATED);
                 }
                 d1++;
             }
             eventTimes.add(d1, pt[p2]);
             xCoords.add(d1, px[p2]);
             yCoords.add(d1, py[p2]);
-            if (GestureTrail.DEBUG_SHOW_POINTS) {
-                types.add(d1, GestureTrail.POINT_TYPE_SAMPLED);
+            if (GestureTrailDrawingPoints.DEBUG_SHOW_POINTS) {
+                types.add(d1, GestureTrailDrawingPoints.POINT_TYPE_SAMPLED);
             }
         }
         return lastInterpolatedDrawIndex;
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeParams.java b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeRecognitionParams.java
similarity index 77%
rename from java/src/com/android/inputmethod/keyboard/internal/GestureStrokeParams.java
rename to java/src/com/android/inputmethod/keyboard/internal/GestureStrokeRecognitionParams.java
index fdae5b9..07b1451 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeParams.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeRecognitionParams.java
@@ -21,7 +21,22 @@
 import com.android.inputmethod.latin.R;
 import com.android.inputmethod.latin.utils.ResourceUtils;
 
-public final class GestureStrokeParams {
+/**
+ * This class holds parameters to control how a gesture stroke is sampled and recognized.
+ * This class also has parameters to distinguish gesture input events from fast typing events.
+ *
+ * @attr ref R.styleable#MainKeyboardView_gestureStaticTimeThresholdAfterFastTyping
+ * @attr ref R.styleable#MainKeyboardView_gestureDetectFastMoveSpeedThreshold
+ * @attr ref R.styleable#MainKeyboardView_gestureDynamicThresholdDecayDuration
+ * @attr ref R.styleable#MainKeyboardView_gestureDynamicTimeThresholdFrom
+ * @attr ref R.styleable#MainKeyboardView_gestureDynamicTimeThresholdTo
+ * @attr ref R.styleable#MainKeyboardView_gestureDynamicDistanceThresholdFrom
+ * @attr ref R.styleable#MainKeyboardView_gestureDynamicDistanceThresholdTo
+ * @attr ref R.styleable#MainKeyboardView_gestureSamplingMinimumDistance
+ * @attr ref R.styleable#MainKeyboardView_gestureRecognitionMinimumTime
+ * @attr ref R.styleable#MainKeyboardView_gestureRecognitionSpeedThreshold
+ */
+public final class GestureStrokeRecognitionParams {
     // Static threshold for gesture after fast typing
     public final int mStaticTimeThresholdAfterFastTyping; // msec
     // Static threshold for starting gesture detection
@@ -40,10 +55,11 @@
     public final int mRecognitionMinimumTime; // msec
     public final float mRecognitionSpeedThreshold; // keyWidth/sec
 
-    // Default GestureStroke parameters.
-    public static final GestureStrokeParams DEFAULT = new GestureStrokeParams();
+    // Default GestureStrokeRecognitionPoints parameters.
+    public static final GestureStrokeRecognitionParams DEFAULT =
+            new GestureStrokeRecognitionParams();
 
-    private GestureStrokeParams() {
+    private GestureStrokeRecognitionParams() {
         // These parameter values are default and intended for testing.
         mStaticTimeThresholdAfterFastTyping = 350; // msec
         mDetectFastMoveSpeedThreshold = 1.5f; // keyWidth/sec
@@ -58,7 +74,7 @@
         mRecognitionSpeedThreshold = 5.5f; // keyWidth/sec
     }
 
-    public GestureStrokeParams(final TypedArray mainKeyboardViewAttr) {
+    public GestureStrokeRecognitionParams(final TypedArray mainKeyboardViewAttr) {
         mStaticTimeThresholdAfterFastTyping = mainKeyboardViewAttr.getInt(
                 R.styleable.MainKeyboardView_gestureStaticTimeThresholdAfterFastTyping,
                 DEFAULT.mStaticTimeThresholdAfterFastTyping);
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureStroke.java b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeRecognitionPoints.java
similarity index 84%
rename from java/src/com/android/inputmethod/keyboard/internal/GestureStroke.java
rename to java/src/com/android/inputmethod/keyboard/internal/GestureStrokeRecognitionPoints.java
index 605d53f..343c898 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GestureStroke.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeRecognitionPoints.java
@@ -21,8 +21,12 @@
 import com.android.inputmethod.latin.InputPointers;
 import com.android.inputmethod.latin.utils.ResizableIntArray;
 
-public class GestureStroke {
-    private static final String TAG = GestureStroke.class.getSimpleName();
+/**
+ * This class holds event points to recognize a gesture stroke.
+ * TODO: Should be final and package private class.
+ */
+public class GestureStrokeRecognitionPoints {
+    private static final String TAG = GestureStrokeRecognitionPoints.class.getSimpleName();
     private static final boolean DEBUG = false;
     private static final boolean DEBUG_SPEED = false;
 
@@ -37,7 +41,7 @@
     private final ResizableIntArray mXCoordinates = new ResizableIntArray(DEFAULT_CAPACITY);
     private final ResizableIntArray mYCoordinates = new ResizableIntArray(DEFAULT_CAPACITY);
 
-    private final GestureStrokeParams mParams;
+    private final GestureStrokeRecognitionParams mRecognitionParams;
 
     private int mKeyWidth; // pixel
     private int mMinYCoordinate; // pixel
@@ -63,9 +67,10 @@
 
     private static final int MSEC_PER_SEC = 1000;
 
-    public GestureStroke(final int pointerId, final GestureStrokeParams params) {
+    public GestureStrokeRecognitionPoints(final int pointerId,
+            final GestureStrokeRecognitionParams recognitionParams) {
         mPointerId = pointerId;
-        mParams = params;
+        mRecognitionParams = recognitionParams;
     }
 
     public void setKeyboardGeometry(final int keyWidth, final int keyboardHeight) {
@@ -73,18 +78,22 @@
         mMinYCoordinate = -(int)(keyboardHeight * EXTRA_GESTURE_TRAIL_AREA_ABOVE_KEYBOARD_RATIO);
         mMaxYCoordinate = keyboardHeight;
         // TODO: Find an appropriate base metric for these length. Maybe diagonal length of the key?
-        mDetectFastMoveSpeedThreshold = (int)(keyWidth * mParams.mDetectFastMoveSpeedThreshold);
-        mGestureDynamicDistanceThresholdFrom =
-                (int)(keyWidth * mParams.mDynamicDistanceThresholdFrom);
-        mGestureDynamicDistanceThresholdTo = (int)(keyWidth * mParams.mDynamicDistanceThresholdTo);
-        mGestureSamplingMinimumDistance = (int)(keyWidth * mParams.mSamplingMinimumDistance);
-        mGestureRecognitionSpeedThreshold = (int)(keyWidth * mParams.mRecognitionSpeedThreshold);
+        mDetectFastMoveSpeedThreshold = (int)(
+                keyWidth * mRecognitionParams.mDetectFastMoveSpeedThreshold);
+        mGestureDynamicDistanceThresholdFrom = (int)(
+                keyWidth * mRecognitionParams.mDynamicDistanceThresholdFrom);
+        mGestureDynamicDistanceThresholdTo = (int)(
+                keyWidth * mRecognitionParams.mDynamicDistanceThresholdTo);
+        mGestureSamplingMinimumDistance = (int)(
+                keyWidth * mRecognitionParams.mSamplingMinimumDistance);
+        mGestureRecognitionSpeedThreshold = (int)(
+                keyWidth * mRecognitionParams.mRecognitionSpeedThreshold);
         if (DEBUG) {
             Log.d(TAG, String.format(
                     "[%d] setKeyboardGeometry: keyWidth=%3d tT=%3d >> %3d tD=%3d >> %3d",
                     mPointerId, keyWidth,
-                    mParams.mDynamicTimeThresholdFrom,
-                    mParams.mDynamicTimeThresholdTo,
+                    mRecognitionParams.mDynamicTimeThresholdFrom,
+                    mRecognitionParams.mDynamicTimeThresholdTo,
                     mGestureDynamicDistanceThresholdFrom,
                     mGestureDynamicDistanceThresholdTo));
         }
@@ -98,7 +107,7 @@
             final long gestureFirstDownTime, final long lastTypingTime) {
         reset();
         final long elapsedTimeAfterTyping = downTime - lastTypingTime;
-        if (elapsedTimeAfterTyping < mParams.mStaticTimeThresholdAfterFastTyping) {
+        if (elapsedTimeAfterTyping < mRecognitionParams.mStaticTimeThresholdAfterFastTyping) {
             mAfterFastTyping = true;
         }
         if (DEBUG) {
@@ -110,23 +119,24 @@
     }
 
     private int getGestureDynamicDistanceThreshold(final int deltaTime) {
-        if (!mAfterFastTyping || deltaTime >= mParams.mDynamicThresholdDecayDuration) {
+        if (!mAfterFastTyping || deltaTime >= mRecognitionParams.mDynamicThresholdDecayDuration) {
             return mGestureDynamicDistanceThresholdTo;
         }
         final int decayedThreshold =
                 (mGestureDynamicDistanceThresholdFrom - mGestureDynamicDistanceThresholdTo)
-                * deltaTime / mParams.mDynamicThresholdDecayDuration;
+                * deltaTime / mRecognitionParams.mDynamicThresholdDecayDuration;
         return mGestureDynamicDistanceThresholdFrom - decayedThreshold;
     }
 
     private int getGestureDynamicTimeThreshold(final int deltaTime) {
-        if (!mAfterFastTyping || deltaTime >= mParams.mDynamicThresholdDecayDuration) {
-            return mParams.mDynamicTimeThresholdTo;
+        if (!mAfterFastTyping || deltaTime >= mRecognitionParams.mDynamicThresholdDecayDuration) {
+            return mRecognitionParams.mDynamicTimeThresholdTo;
         }
         final int decayedThreshold =
-                (mParams.mDynamicTimeThresholdFrom - mParams.mDynamicTimeThresholdTo)
-                * deltaTime / mParams.mDynamicThresholdDecayDuration;
-        return mParams.mDynamicTimeThresholdFrom - decayedThreshold;
+                (mRecognitionParams.mDynamicTimeThresholdFrom
+                        - mRecognitionParams.mDynamicTimeThresholdTo)
+                * deltaTime / mRecognitionParams.mDynamicThresholdDecayDuration;
+        return mRecognitionParams.mDynamicTimeThresholdFrom - decayedThreshold;
     }
 
     public final boolean isStartOfAGesture() {
@@ -285,7 +295,7 @@
 
     public final boolean hasRecognitionTimePast(
             final long currentTime, final long lastRecognitionTime) {
-        return currentTime > lastRecognitionTime + mParams.mRecognitionMinimumTime;
+        return currentTime > lastRecognitionTime + mRecognitionParams.mRecognitionMinimumTime;
     }
 
     public final void appendAllBatchPoints(final InputPointers out) {
@@ -307,10 +317,6 @@
     }
 
     private static int getDistance(final int x1, final int y1, final int x2, final int y2) {
-        final int dx = x1 - x2;
-        final int dy = y1 - y2;
-        // Note that, in recent versions of Android, FloatMath is actually slower than
-        // java.lang.Math due to the way the JIT optimizes java.lang.Math.
-        return (int)Math.sqrt(dx * dx + dy * dy);
+        return (int)Math.hypot(x1 - x2, y1 - y2);
     }
 }
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureTrailDrawingParams.java b/java/src/com/android/inputmethod/keyboard/internal/GestureTrailDrawingParams.java
new file mode 100644
index 0000000..088f03a
--- /dev/null
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureTrailDrawingParams.java
@@ -0,0 +1,79 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.keyboard.internal;
+
+import android.content.res.TypedArray;
+
+import com.android.inputmethod.latin.R;
+
+/**
+ * This class holds parameters to control how a gesture trail is drawn and animated on the screen.
+ *
+ * On the other hand, {@link GestureStrokeDrawingParams} class controls how each gesture stroke is
+ * sampled and interpolated. This class controls how those gesture strokes are displayed as a
+ * gesture trail and animated on the screen.
+ *
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailFadeoutStartDelay
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailFadeoutDuration
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailUpdateInterval
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailColor
+ * @attr ref R.styleable#MainKeyboardView_gestureTrailWidth
+ */
+final class GestureTrailDrawingParams {
+    private static final int FADEOUT_START_DELAY_FOR_DEBUG = 2000; // millisecond
+    private static final int FADEOUT_DURATION_FOR_DEBUG = 200; // millisecond
+
+    public final int mTrailColor;
+    public final float mTrailStartWidth;
+    public final float mTrailEndWidth;
+    public final float mTrailBodyRatio;
+    public boolean mTrailShadowEnabled;
+    public final float mTrailShadowRatio;
+    public final int mFadeoutStartDelay;
+    public final int mFadeoutDuration;
+    public final int mUpdateInterval;
+
+    public final int mTrailLingerDuration;
+
+    public GestureTrailDrawingParams(final TypedArray mainKeyboardViewAttr) {
+        mTrailColor = mainKeyboardViewAttr.getColor(
+                R.styleable.MainKeyboardView_gestureTrailColor, 0);
+        mTrailStartWidth = mainKeyboardViewAttr.getDimension(
+                R.styleable.MainKeyboardView_gestureTrailStartWidth, 0.0f);
+        mTrailEndWidth = mainKeyboardViewAttr.getDimension(
+                R.styleable.MainKeyboardView_gestureTrailEndWidth, 0.0f);
+        final int PERCENTAGE_INT = 100;
+        mTrailBodyRatio = (float)mainKeyboardViewAttr.getInt(
+                R.styleable.MainKeyboardView_gestureTrailBodyRatio, PERCENTAGE_INT)
+                / (float)PERCENTAGE_INT;
+        final int trailShadowRatioInt = mainKeyboardViewAttr.getInt(
+                R.styleable.MainKeyboardView_gestureTrailShadowRatio, 0);
+        mTrailShadowEnabled = (trailShadowRatioInt > 0);
+        mTrailShadowRatio = (float)trailShadowRatioInt / (float)PERCENTAGE_INT;
+        mFadeoutStartDelay = GestureTrailDrawingPoints.DEBUG_SHOW_POINTS
+                ? FADEOUT_START_DELAY_FOR_DEBUG
+                : mainKeyboardViewAttr.getInt(
+                        R.styleable.MainKeyboardView_gestureTrailFadeoutStartDelay, 0);
+        mFadeoutDuration = GestureTrailDrawingPoints.DEBUG_SHOW_POINTS
+                ? FADEOUT_DURATION_FOR_DEBUG
+                : mainKeyboardViewAttr.getInt(
+                        R.styleable.MainKeyboardView_gestureTrailFadeoutDuration, 0);
+        mTrailLingerDuration = mFadeoutStartDelay + mFadeoutDuration;
+        mUpdateInterval = mainKeyboardViewAttr.getInt(
+                R.styleable.MainKeyboardView_gestureTrailUpdateInterval, 0);
+    }
+}
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureTrail.java b/java/src/com/android/inputmethod/keyboard/internal/GestureTrailDrawingPoints.java
similarity index 77%
rename from java/src/com/android/inputmethod/keyboard/internal/GestureTrail.java
rename to java/src/com/android/inputmethod/keyboard/internal/GestureTrailDrawingPoints.java
index aca6679..bf4c4da 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GestureTrail.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureTrailDrawingPoints.java
@@ -16,7 +16,6 @@
 
 package com.android.inputmethod.keyboard.internal;
 
-import android.content.res.TypedArray;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
@@ -25,24 +24,22 @@
 import android.os.SystemClock;
 
 import com.android.inputmethod.latin.Constants;
-import com.android.inputmethod.latin.R;
 import com.android.inputmethod.latin.utils.ResizableIntArray;
 
-/*
- * @attr ref R.styleable#MainKeyboardView_gestureTrailFadeoutStartDelay
- * @attr ref R.styleable#MainKeyboardView_gestureTrailFadeoutDuration
- * @attr ref R.styleable#MainKeyboardView_gestureTrailUpdateInterval
- * @attr ref R.styleable#MainKeyboardView_gestureTrailColor
- * @attr ref R.styleable#MainKeyboardView_gestureTrailWidth
+/**
+ * This class holds drawing points to represent a gesture trail. The gesture trail may contain
+ * multiple non-contiguous gesture strokes and will be animated asynchronously from gesture input.
+ *
+ * On the other hand, {@link GestureStrokeDrawingPoints} class holds drawing points of each gesture
+ * stroke. This class holds drawing points of those gesture strokes to draw as a gesture trail.
+ * Drawing points in this class will be asynchronously removed when fading out animation goes.
  */
-final class GestureTrail {
+final class GestureTrailDrawingPoints {
     public static final boolean DEBUG_SHOW_POINTS = false;
     public static final int POINT_TYPE_SAMPLED = 1;
     public static final int POINT_TYPE_INTERPOLATED = 2;
-    private static final int FADEOUT_START_DELAY_FOR_DEBUG = 2000; // millisecond
-    private static final int FADEOUT_DURATION_FOR_DEBUG = 200; // millisecond
 
-    private static final int DEFAULT_CAPACITY = GestureStrokeWithPreviewPoints.PREVIEW_CAPACITY;
+    private static final int DEFAULT_CAPACITY = GestureStrokeDrawingPoints.PREVIEW_CAPACITY;
 
     // These three {@link ResizableIntArray}s should be synchronized by {@link #mEventTimes}.
     private final ResizableIntArray mXCoordinates = new ResizableIntArray(DEFAULT_CAPACITY);
@@ -56,46 +53,6 @@
     private int mTrailStartIndex;
     private int mLastInterpolatedDrawIndex;
 
-    static final class Params {
-        public final int mTrailColor;
-        public final float mTrailStartWidth;
-        public final float mTrailEndWidth;
-        public final float mTrailBodyRatio;
-        public boolean mTrailShadowEnabled;
-        public final float mTrailShadowRatio;
-        public final int mFadeoutStartDelay;
-        public final int mFadeoutDuration;
-        public final int mUpdateInterval;
-
-        public final int mTrailLingerDuration;
-
-        public Params(final TypedArray mainKeyboardViewAttr) {
-            mTrailColor = mainKeyboardViewAttr.getColor(
-                    R.styleable.MainKeyboardView_gestureTrailColor, 0);
-            mTrailStartWidth = mainKeyboardViewAttr.getDimension(
-                    R.styleable.MainKeyboardView_gestureTrailStartWidth, 0.0f);
-            mTrailEndWidth = mainKeyboardViewAttr.getDimension(
-                    R.styleable.MainKeyboardView_gestureTrailEndWidth, 0.0f);
-            final int PERCENTAGE_INT = 100;
-            mTrailBodyRatio = (float)mainKeyboardViewAttr.getInt(
-                    R.styleable.MainKeyboardView_gestureTrailBodyRatio, PERCENTAGE_INT)
-                    / (float)PERCENTAGE_INT;
-            final int trailShadowRatioInt = mainKeyboardViewAttr.getInt(
-                    R.styleable.MainKeyboardView_gestureTrailShadowRatio, 0);
-            mTrailShadowEnabled = (trailShadowRatioInt > 0);
-            mTrailShadowRatio = (float)trailShadowRatioInt / (float)PERCENTAGE_INT;
-            mFadeoutStartDelay = DEBUG_SHOW_POINTS ? FADEOUT_START_DELAY_FOR_DEBUG
-                    : mainKeyboardViewAttr.getInt(
-                            R.styleable.MainKeyboardView_gestureTrailFadeoutStartDelay, 0);
-            mFadeoutDuration = DEBUG_SHOW_POINTS ? FADEOUT_DURATION_FOR_DEBUG
-                    : mainKeyboardViewAttr.getInt(
-                            R.styleable.MainKeyboardView_gestureTrailFadeoutDuration, 0);
-            mTrailLingerDuration = mFadeoutStartDelay + mFadeoutDuration;
-            mUpdateInterval = mainKeyboardViewAttr.getInt(
-                    R.styleable.MainKeyboardView_gestureTrailUpdateInterval, 0);
-        }
-    }
-
     // Use this value as imaginary zero because x-coordinates may be zero.
     private static final int DOWN_EVENT_MARKER = -128;
 
@@ -112,13 +69,13 @@
                 ? DOWN_EVENT_MARKER - xCoordOrMark : xCoordOrMark;
     }
 
-    public void addStroke(final GestureStrokeWithPreviewPoints stroke, final long downTime) {
+    public void addStroke(final GestureStrokeDrawingPoints stroke, final long downTime) {
         synchronized (mEventTimes) {
             addStrokeLocked(stroke, downTime);
         }
     }
 
-    private void addStrokeLocked(final GestureStrokeWithPreviewPoints stroke, final long downTime) {
+    private void addStrokeLocked(final GestureStrokeDrawingPoints stroke, final long downTime) {
         final int trailSize = mEventTimes.getLength();
         stroke.appendPreviewStroke(mEventTimes, mXCoordinates, mYCoordinates, mPointTypes);
         if (mEventTimes.getLength() == trailSize) {
@@ -126,13 +83,14 @@
         }
         final int[] eventTimes = mEventTimes.getPrimitiveArray();
         final int strokeId = stroke.getGestureStrokeId();
-        // Because interpolation algorithm in {@link GestureStrokeWithPreviewPoints} can't determine
+        // Because interpolation algorithm in {@link GestureStrokeDrawingPoints} can't determine
         // the interpolated points in the last segment of gesture stroke, it may need recalculation
         // of interpolation when new segments are added to the stroke.
         // {@link #mLastInterpolatedDrawIndex} holds the start index of the last segment. It may
         // be updated by the interpolation
-        // {@link GestureStrokeWithPreviewPoints#interpolatePreviewStroke}
-        // or by animation {@link #drawGestureTrail(Canvas,Paint,Rect,Params)} below.
+        // {@link GestureStrokeDrawingPoints#interpolatePreviewStroke}
+        // or by animation {@link #drawGestureTrail(Canvas,Paint,Rect,GestureTrailDrawingParams)}
+        // below.
         final int lastInterpolatedIndex = (strokeId == mCurrentStrokeId)
                 ? mLastInterpolatedDrawIndex : trailSize;
         mLastInterpolatedDrawIndex = stroke.interpolateStrokeAndReturnStartIndexOfLastSegment(
@@ -161,7 +119,7 @@
      * @param params gesture trail display parameters
      * @return the width of a gesture trail
      */
-    private static int getAlpha(final int elapsedTime, final Params params) {
+    private static int getAlpha(final int elapsedTime, final GestureTrailDrawingParams params) {
         if (elapsedTime < params.mFadeoutStartDelay) {
             return Constants.Color.ALPHA_OPAQUE;
         }
@@ -180,7 +138,7 @@
      * @param params gesture trail display parameters
      * @return the width of a gesture trail
      */
-    private static float getWidth(final int elapsedTime, final Params params) {
+    private static float getWidth(final int elapsedTime, final GestureTrailDrawingParams params) {
         final float deltaWidth = params.mTrailStartWidth - params.mTrailEndWidth;
         return params.mTrailStartWidth - (deltaWidth * elapsedTime) / params.mTrailLingerDuration;
     }
@@ -197,14 +155,14 @@
      * @return true if some gesture trails remain to be drawn
      */
     public boolean drawGestureTrail(final Canvas canvas, final Paint paint,
-            final Rect outBoundsRect, final Params params) {
+            final Rect outBoundsRect, final GestureTrailDrawingParams params) {
         synchronized (mEventTimes) {
             return drawGestureTrailLocked(canvas, paint, outBoundsRect, params);
         }
     }
 
     private boolean drawGestureTrailLocked(final Canvas canvas, final Paint paint,
-            final Rect outBoundsRect, final Params params) {
+            final Rect outBoundsRect, final GestureTrailDrawingParams params) {
         // Initialize bounds rectangle.
         outBoundsRect.setEmpty();
         final int trailSize = mEventTimes.getLength();
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureTrailsDrawingPreview.java b/java/src/com/android/inputmethod/keyboard/internal/GestureTrailsDrawingPreview.java
index 13f2b60..eef4b36 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GestureTrailsDrawingPreview.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureTrailsDrawingPreview.java
@@ -29,16 +29,16 @@
 import android.view.View;
 
 import com.android.inputmethod.keyboard.PointerTracker;
-import com.android.inputmethod.keyboard.internal.GestureTrail.Params;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 import com.android.inputmethod.latin.utils.LeakGuardHandlerWrapper;
 
 /**
- * Draw gesture trail preview graphics during gesture.
+ * Draw preview graphics of multiple gesture trails during gesture input.
  */
 public final class GestureTrailsDrawingPreview extends AbstractDrawingPreview {
-    private final SparseArray<GestureTrail> mGestureTrails = CollectionUtils.newSparseArray();
-    private final Params mGestureTrailParams;
+    private final SparseArray<GestureTrailDrawingPoints> mGestureTrails =
+            CollectionUtils.newSparseArray();
+    private final GestureTrailDrawingParams mDrawingParams;
     private final Paint mGesturePaint;
     private int mOffscreenWidth;
     private int mOffscreenHeight;
@@ -55,12 +55,12 @@
             extends LeakGuardHandlerWrapper<GestureTrailsDrawingPreview> {
         private static final int MSG_UPDATE_GESTURE_TRAIL = 0;
 
-        private final Params mGestureTrailParams;
+        private final GestureTrailDrawingParams mDrawingParams;
 
         public DrawingHandler(final GestureTrailsDrawingPreview ownerInstance,
-                final Params gestureTrailParams) {
+                final GestureTrailDrawingParams drawingParams) {
             super(ownerInstance);
-            mGestureTrailParams = gestureTrailParams;
+            mDrawingParams = drawingParams;
         }
 
         @Override
@@ -79,15 +79,15 @@
         public void postUpdateGestureTrailPreview() {
             removeMessages(MSG_UPDATE_GESTURE_TRAIL);
             sendMessageDelayed(obtainMessage(MSG_UPDATE_GESTURE_TRAIL),
-                    mGestureTrailParams.mUpdateInterval);
+                    mDrawingParams.mUpdateInterval);
         }
     }
 
     public GestureTrailsDrawingPreview(final View drawingView,
             final TypedArray mainKeyboardViewAttr) {
         super(drawingView);
-        mGestureTrailParams = new Params(mainKeyboardViewAttr);
-        mDrawingHandler = new DrawingHandler(this, mGestureTrailParams);
+        mDrawingParams = new GestureTrailDrawingParams(mainKeyboardViewAttr);
+        mDrawingHandler = new DrawingHandler(this, mDrawingParams);
         final Paint gesturePaint = new Paint();
         gesturePaint.setAntiAlias(true);
         gesturePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
@@ -96,8 +96,8 @@
 
     @Override
     public void setKeyboardGeometry(final int[] originCoords, final int width, final int height) {
-        mOffscreenOffsetY = (int)(
-                height * GestureStroke.EXTRA_GESTURE_TRAIL_AREA_ABOVE_KEYBOARD_RATIO);
+        mOffscreenOffsetY = (int)(height
+                * GestureStrokeRecognitionPoints.EXTRA_GESTURE_TRAIL_AREA_ABOVE_KEYBOARD_RATIO);
         mOffscreenWidth = width;
         mOffscreenHeight = mOffscreenOffsetY + height;
     }
@@ -143,9 +143,9 @@
             // Trails count == fingers count that have ever been active.
             final int trailsCount = mGestureTrails.size();
             for (int index = 0; index < trailsCount; index++) {
-                final GestureTrail trail = mGestureTrails.valueAt(index);
+                final GestureTrailDrawingPoints trail = mGestureTrails.valueAt(index);
                 needsUpdatingGestureTrail |= trail.drawGestureTrail(offscreenCanvas, paint,
-                        mGestureTrailBoundsRect, mGestureTrailParams);
+                        mGestureTrailBoundsRect, mDrawingParams);
                 // {@link #mGestureTrailBoundsRect} has bounding box of the trail.
                 dirtyRect.union(mGestureTrailBoundsRect);
             }
@@ -188,15 +188,15 @@
         if (!isPreviewEnabled()) {
             return;
         }
-        GestureTrail trail;
+        GestureTrailDrawingPoints trail;
         synchronized (mGestureTrails) {
             trail = mGestureTrails.get(tracker.mPointerId);
             if (trail == null) {
-                trail = new GestureTrail();
+                trail = new GestureTrailDrawingPoints();
                 mGestureTrails.put(tracker.mPointerId, trail);
             }
         }
-        trail.addStroke(tracker.getGestureStrokeWithPreviewPoints(), tracker.getDownTime());
+        trail.addStroke(tracker.getGestureStrokeDrawingPoints(), tracker.getDownTime());
 
         // TODO: Should narrow the invalidate region.
         getDrawingView().invalidate();