Use Path to draw gesture preview trail

This change also reduces the number of points to use as preview trail.

Bug: 7167303
Change-Id: I0cf4908efa44b17b42d4fddd6725238236ac2654

java/src/com/android/inputmethod/keyboard/PointerTracker.java

@@ -23,7 +23,7 @@ import android.view.MotionEvent;
 
 import com.android.inputmethod.accessibility.AccessibilityUtils;
 import com.android.inputmethod.keyboard.internal.GestureStroke;
-import com.android.inputmethod.keyboard.internal.GestureStrokeWithPreviewTrail;
+import com.android.inputmethod.keyboard.internal.GestureStrokeWithPreviewPoints;
 import com.android.inputmethod.keyboard.internal.PointerTrackerQueue;
 import com.android.inputmethod.latin.CollectionUtils;
 import com.android.inputmethod.latin.InputPointers;
@@ -208,7 +208,7 @@ public class PointerTracker implements PointerTrackerQueue.Element {
     private static final KeyboardActionListener EMPTY_LISTENER =
             new KeyboardActionListener.Adapter();
 
-    private final GestureStrokeWithPreviewTrail mGestureStrokeWithPreviewTrail;
+    private final GestureStrokeWithPreviewPoints mGestureStrokeWithPreviewPoints;
 
     public static void init(boolean hasDistinctMultitouch,
             boolean needsPhantomSuddenMoveEventHack) {
@@ -293,7 +293,7 @@ public class PointerTracker implements PointerTrackerQueue.Element {
             throw new NullPointerException();
         }
         mPointerId = id;
-        mGestureStrokeWithPreviewTrail = new GestureStrokeWithPreviewTrail(id);
+        mGestureStrokeWithPreviewPoints = new GestureStrokeWithPreviewPoints(id);
         setKeyDetectorInner(handler.getKeyDetector());
         mListener = handler.getKeyboardActionListener();
         mDrawingProxy = handler.getDrawingProxy();
@@ -392,7 +392,7 @@ public class PointerTracker implements PointerTrackerQueue.Element {
     private void setKeyDetectorInner(final KeyDetector keyDetector) {
         mKeyDetector = keyDetector;
         mKeyboard = keyDetector.getKeyboard();
-        mGestureStrokeWithPreviewTrail.setGestureSampleLength(mKeyboard.mMostCommonKeyWidth);
+        mGestureStrokeWithPreviewPoints.setKeyboardGeometry(mKeyboard.mMostCommonKeyWidth);
         final Key newKey = mKeyDetector.detectHitKey(mKeyX, mKeyY);
         if (newKey != mCurrentKey) {
             if (mDrawingProxy != null) {
@@ -502,8 +502,8 @@ public class PointerTracker implements PointerTrackerQueue.Element {
         mDrawingProxy.invalidateKey(key);
     }
 
-    public GestureStrokeWithPreviewTrail getGestureStrokeWithPreviewTrail() {
+    public GestureStrokeWithPreviewPoints getGestureStrokeWithPreviewPoints() {
-        return mGestureStrokeWithPreviewTrail;
+        return mGestureStrokeWithPreviewPoints;
     }
 
     public int getLastX() {
@@ -544,8 +544,8 @@ public class PointerTracker implements PointerTrackerQueue.Element {
         return (sPointerTrackerQueue == null) ? 1 : sPointerTrackerQueue.size();
     }
 
-    private void startBatchInput() {
+    private void mayStartBatchInput() {
-        if (sInGesture || !mGestureStrokeWithPreviewTrail.isStartOfAGesture()) {
+        if (sInGesture || !mGestureStrokeWithPreviewPoints.isStartOfAGesture()) {
             return;
         }
         if (DEBUG_LISTENER) {
@@ -559,7 +559,7 @@ public class PointerTracker implements PointerTrackerQueue.Element {
 
     private void updateBatchInput(final long eventTime) {
         synchronized (sAggregratedPointers) {
-            mGestureStrokeWithPreviewTrail.appendIncrementalBatchPoints(sAggregratedPointers);
+            mGestureStrokeWithPreviewPoints.appendIncrementalBatchPoints(sAggregratedPointers);
             final int size = sAggregratedPointers.getPointerSize();
             if (size > sLastRecognitionPointSize
                     && eventTime > sLastRecognitionTime + MIN_GESTURE_RECOGNITION_TIME) {
@@ -575,10 +575,10 @@ public class PointerTracker implements PointerTrackerQueue.Element {
         mDrawingProxy.showGesturePreviewTrail(this, isOldestTracker);
     }
 
-    private void endBatchInput() {
+    private void mayEndBatchInput() {
         synchronized (sAggregratedPointers) {
-            mGestureStrokeWithPreviewTrail.appendAllBatchPoints(sAggregratedPointers);
+            mGestureStrokeWithPreviewPoints.appendAllBatchPoints(sAggregratedPointers);
-            mGestureStrokeWithPreviewTrail.reset();
+            mGestureStrokeWithPreviewPoints.reset();
             if (getActivePointerTrackerCount() == 1) {
                 if (DEBUG_LISTENER) {
                     Log.d(TAG, "onEndBatchInput: batchPoints="
@@ -601,7 +601,7 @@ public class PointerTracker implements PointerTrackerQueue.Element {
         final int trackersSize = sTrackers.size();
         for (int i = 0; i < trackersSize; ++i) {
             final PointerTracker tracker = sTrackers.get(i);
-            tracker.mGestureStrokeWithPreviewTrail.reset();
+            tracker.mGestureStrokeWithPreviewPoints.reset();
         }
         sAggregratedPointers.reset();
         sLastRecognitionPointSize = 0;
@@ -678,17 +678,20 @@ public class PointerTracker implements PointerTrackerQueue.Element {
                     && mKeyboard.mId.isAlphabetKeyboard();
             if (isAlphabetKeyboard && !mIsShowingMoreKeysPanel && key != null
                     && Keyboard.isLetterCode(key.mCode)) {
-                mIsDetectingGesture = true;
                 sGestureFirstDownTime = eventTime;
-                mGestureStrokeWithPreviewTrail.addPoint(x, y, 0, false /* isHistorical */);
+                onGestureDownEvent(x, y, eventTime);
             }
         } else if (sInGesture && activePointerTrackerCount > 1) {
+            onGestureDownEvent(x, y, eventTime);
+        }
+    }
+
+    private void onGestureDownEvent(final int x, final int y, final long eventTime) {
         mIsDetectingGesture = true;
         final int elapsedTimeFromFirstDown = (int)(eventTime - sGestureFirstDownTime);
-            mGestureStrokeWithPreviewTrail.addPoint(x, y, elapsedTimeFromFirstDown,
+        mGestureStrokeWithPreviewPoints.addPoint(x, y, elapsedTimeFromFirstDown,
                 false /* isHistorical */);
     }
-    }
 
     private void onDownEventInternal(final int x, final int y, final long eventTime) {
         Key key = onDownKey(x, y, eventTime);
@@ -726,8 +729,8 @@ public class PointerTracker implements PointerTrackerQueue.Element {
             final boolean isHistorical, final Key key) {
         final int gestureTime = (int)(eventTime - sGestureFirstDownTime);
         if (mIsDetectingGesture) {
-            mGestureStrokeWithPreviewTrail.addPoint(x, y, gestureTime, isHistorical);
+            mGestureStrokeWithPreviewPoints.addPoint(x, y, gestureTime, isHistorical);
-            startBatchInput();
+            mayStartBatchInput();
             if (sInGesture && key != null) {
                 updateBatchInput(eventTime);
             }
@@ -919,7 +922,7 @@ public class PointerTracker implements PointerTrackerQueue.Element {
             if (currentKey != null) {
                 callListenerOnRelease(currentKey, currentKey.mCode, true);
             }
-            endBatchInput();
+            mayEndBatchInput();
             return;
         }
         // This event will be recognized as a regular code input. Clear unused possible batch points

java/src/com/android/inputmethod/keyboard/internal/GesturePreviewTrail.java

@@ -17,7 +17,9 @@ package com.android.inputmethod.keyboard.internal;
 import android.content.res.TypedArray;
 import android.graphics.Canvas;
 import android.graphics.Paint;
+import android.graphics.Path;
 import android.graphics.Rect;
+import android.graphics.RectF;
 import android.os.SystemClock;
 
 import com.android.inputmethod.latin.Constants;
@@ -25,7 +27,7 @@ import com.android.inputmethod.latin.R;
 import com.android.inputmethod.latin.ResizableIntArray;
 
 final class GesturePreviewTrail {
-    private static final int DEFAULT_CAPACITY = GestureStrokeWithPreviewTrail.PREVIEW_CAPACITY;
+    private static final int DEFAULT_CAPACITY = GestureStrokeWithPreviewPoints.PREVIEW_CAPACITY;
 
     private final ResizableIntArray mXCoordinates = new ResizableIntArray(DEFAULT_CAPACITY);
     private final ResizableIntArray mYCoordinates = new ResizableIntArray(DEFAULT_CAPACITY);
@@ -78,7 +80,7 @@ final class GesturePreviewTrail {
                 ? DOWN_EVENT_MARKER - xCoordOrMark : xCoordOrMark;
     }
 
-    public void addStroke(final GestureStrokeWithPreviewTrail stroke, final long downTime) {
+    public void addStroke(final GestureStrokeWithPreviewPoints stroke, final long downTime) {
         final int trailSize = mEventTimes.getLength();
         stroke.appendPreviewStroke(mEventTimes, mXCoordinates, mYCoordinates);
         if (mEventTimes.getLength() == trailSize) {
@@ -116,6 +118,99 @@ final class GesturePreviewTrail {
                 / params.mTrailLingerDuration, 0.0f);
     }
 
+    static final class WorkingSet {
+        // Input
+        // Previous point (P1) coordinates and trail radius.
+        public float p1x, p1y;
+        public float r1;
+        // Current point (P2) coordinates and trail radius.
+        public float p2x, p2y;
+        public float r2;
+
+        // Output
+        // Closing point of arc at P1.
+        public float p1ax, p1ay;
+        // Opening point of arc at P1.
+        public float p1bx, p1by;
+        // Opening point of arc at P2.
+        public float p2ax, p2ay;
+        // Closing point of arc at P2.
+        public float p2bx, p2by;
+        // Start angle of the trail arcs.
+        public float aa;
+        // Sweep angle of the trail arc at P1.
+        public float a1;
+        public RectF arc1 = new RectF();
+        // Sweep angle of the trail arc at P2.
+        public float a2;
+        public RectF arc2 = new RectF();
+    }
+
+    private static final float RIGHT_ANGLE = (float)(Math.PI / 2.0d);
+    private static final float RADIAN_TO_DEGREE = (float)(180.0d / Math.PI);
+
+    private static boolean calculatePathPoints(final WorkingSet w) {
+        final float dx = w.p2x - w.p1x;
+        final float dy = w.p2y - w.p1y;
+        // Distance of the points.
+        final double l = Math.hypot(dx, dy);
+        if (Double.compare(0.0d, l) == 0) {
+            return false;
+        }
+        // Angle of the line p1-p2
+        final float a = (float)Math.atan2(dy, dx);
+        // Difference of trail cap radius.
+        final float dr = w.r2 - w.r1;
+        // Variation of angle at trail cap.
+        final float ar = (float)Math.asin(dr / l);
+        // The start angle of trail cap arc at P1.
+        final float aa = a - (RIGHT_ANGLE + ar);
+        // The end angle of trail cap arc at P2.
+        final float ab = a + (RIGHT_ANGLE + ar);
+        final float cosa = (float)Math.cos(aa);
+        final float sina = (float)Math.sin(aa);
+        final float cosb = (float)Math.cos(ab);
+        final float sinb = (float)Math.sin(ab);
+        w.p1ax = w.p1x + w.r1 * cosa;
+        w.p1ay = w.p1y + w.r1 * sina;
+        w.p1bx = w.p1x + w.r1 * cosb;
+        w.p1by = w.p1y + w.r1 * sinb;
+        w.p2ax = w.p2x + w.r2 * cosa;
+        w.p2ay = w.p2y + w.r2 * sina;
+        w.p2bx = w.p2x + w.r2 * cosb;
+        w.p2by = w.p2y + w.r2 * sinb;
+        w.aa = aa * RADIAN_TO_DEGREE;
+        final float ar2degree = ar * 2.0f * RADIAN_TO_DEGREE;
+        w.a1 = -180.0f + ar2degree;
+        w.a2 = 180.0f + ar2degree;
+        w.arc1.set(w.p1x, w.p1y, w.p1x, w.p1y);
+        w.arc1.inset(-w.r1, -w.r1);
+        w.arc2.set(w.p2x, w.p2y, w.p2x, w.p2y);
+        w.arc2.inset(-w.r2, -w.r2);
+        return true;
+    }
+
+    private static void createPath(final Path path, final WorkingSet w) {
+        path.rewind();
+        // Trail cap at P1.
+        path.moveTo(w.p1x, w.p1y);
+        path.arcTo(w.arc1, w.aa, w.a1);
+        // Trail cap at P2.
+        path.moveTo(w.p2x, w.p2y);
+        path.arcTo(w.arc2, w.aa, w.a2);
+        // Two trapezoids connecting P1 and P2.
+        path.moveTo(w.p1ax, w.p1ay);
+        path.lineTo(w.p1x, w.p1y);
+        path.lineTo(w.p1bx, w.p1by);
+        path.lineTo(w.p2bx, w.p2by);
+        path.lineTo(w.p2x, w.p2y);
+        path.lineTo(w.p2ax, w.p2ay);
+        path.close();
+    }
+
+    private final WorkingSet mWorkingSet = new WorkingSet();
+    private final Path mPath = new Path();
+
     /**
      * Draw gesture preview trail
      * @param canvas The canvas to draw the gesture preview trail
@@ -147,30 +242,38 @@ final class GesturePreviewTrail {
 
         if (startIndex < trailSize) {
             paint.setColor(params.mTrailColor);
-            paint.setStyle(Paint.Style.STROKE);
+            paint.setStyle(Paint.Style.FILL);
-            paint.setStrokeCap(Paint.Cap.ROUND);
+            final Path path = mPath;
-            int lastX = getXCoordValue(xCoords[startIndex]);
+            final WorkingSet w = mWorkingSet;
-            int lastY = yCoords[startIndex];
+            w.p1x = getXCoordValue(xCoords[startIndex]);
-            float maxWidth = getWidth(sinceDown - eventTimes[startIndex], params);
+            w.p1y = yCoords[startIndex];
+            int lastTime = sinceDown - eventTimes[startIndex];
+            float maxWidth = getWidth(lastTime, params);
+            w.r1 = maxWidth / 2.0f;
             // Initialize bounds rectangle.
-            outBoundsRect.set(lastX, lastY, lastX, lastY);
+            outBoundsRect.set((int)w.p1x, (int)w.p1y, (int)w.p1x, (int)w.p1y);
             for (int i = startIndex + 1; i < trailSize - 1; i++) {
-                final int x = xCoords[i];
-                final int y = yCoords[i];
                 final int elapsedTime = sinceDown - eventTimes[i];
+                w.p2x = getXCoordValue(xCoords[i]);
+                w.p2y = yCoords[i];
                 // Draw trail line only when the current point isn't a down point.
-                if (!isDownEventXCoord(x)) {
+                if (!isDownEventXCoord(xCoords[i])) {
                     final int alpha = getAlpha(elapsedTime, params);
                     paint.setAlpha(alpha);
                     final float width = getWidth(elapsedTime, params);
-                    paint.setStrokeWidth(width);
+                    w.r2 = width / 2.0f;
-                    canvas.drawLine(lastX, lastY, x, y, paint);
+                    if (calculatePathPoints(w)) {
+                        createPath(path, w);
+                        canvas.drawPath(path, paint);
+                        outBoundsRect.union((int)w.p2x, (int)w.p2y);
+                    }
                     // Take union for the bounds.
-                    outBoundsRect.union(x, y);
                     maxWidth = Math.max(maxWidth, width);
                 }
-                lastX = getXCoordValue(x);
+                w.p1x = w.p2x;
-                lastY = y;
+                w.p1y = w.p2y;
+                w.r1 = w.r2;
+                lastTime = elapsedTime;
             }
             // Take care of trail line width.
             final int inset = -((int)maxWidth + 1);

java/src/com/android/inputmethod/keyboard/internal/GestureStroke.java

@@ -44,7 +44,7 @@ public class GestureStroke {
         mPointerId = pointerId;
     }
 
-    public void setGestureSampleLength(final int keyWidth) {
+    public void setKeyboardGeometry(final int keyWidth) {
         // TODO: Find an appropriate base metric for these length. Maybe diagonal length of the key?
         mMinGestureLength = (int)(keyWidth * MIN_GESTURE_LENGTH_RATIO_TO_KEY_WIDTH);
         mMinGestureSampleLength = (int)(keyWidth * MIN_GESTURE_SAMPLING_RATIO_TO_KEY_WIDTH);

java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java

@@ -16,7 +16,7 @@ package com.android.inputmethod.keyboard.internal;
 
 import com.android.inputmethod.latin.ResizableIntArray;
 
-public class GestureStrokeWithPreviewTrail extends GestureStroke {
+public class GestureStrokeWithPreviewPoints extends GestureStroke {
     public static final int PREVIEW_CAPACITY = 256;
 
     private final ResizableIntArray mPreviewEventTimes = new ResizableIntArray(PREVIEW_CAPACITY);
@@ -26,7 +26,14 @@ public class GestureStrokeWithPreviewTrail extends GestureStroke {
     private int mStrokeId;
     private int mLastPreviewSize;
 
-    public GestureStrokeWithPreviewTrail(final int pointerId) {
+    private int mMinPreviewSampleLengthSquare;
+    private int mLastX;
+    private int mLastY;
+
+    // TODO: Move this to resource.
+    private static final float MIN_PREVIEW_SAMPLE_LENGTH_RATIO_TO_KEY_WIDTH = 0.1f;
+
+    public GestureStrokeWithPreviewPoints(final int pointerId) {
         super(pointerId);
     }
 
@@ -48,13 +55,33 @@ public class GestureStrokeWithPreviewTrail extends GestureStroke {
         return mPreviewEventTimes.getLength();
     }
 
+    @Override
+    public void setKeyboardGeometry(final int keyWidth) {
+        super.setKeyboardGeometry(keyWidth);
+        final float sampleLength = keyWidth * MIN_PREVIEW_SAMPLE_LENGTH_RATIO_TO_KEY_WIDTH;
+        mMinPreviewSampleLengthSquare = (int)(sampleLength * sampleLength);
+    }
+
+    private boolean needsSampling(final int x, final int y) {
+        final int dx = x - mLastX;
+        final int dy = y - mLastY;
+        final boolean needsSampling = (dx * dx + dy * dy >= mMinPreviewSampleLengthSquare);
+        if (needsSampling) {
+            mLastX = x;
+            mLastY = y;
+        }
+        return needsSampling;
+    }
+
     @Override
     public void addPoint(final int x, final int y, final int time, final boolean isHistorical) {
         super.addPoint(x, y, time, isHistorical);
+        if (mPreviewEventTimes.getLength() == 0 || isHistorical || needsSampling(x, y)) {
             mPreviewEventTimes.add(time);
             mPreviewXCoordinates.add(x);
             mPreviewYCoordinates.add(y);
         }
+    }
 
     public void appendPreviewStroke(final ResizableIntArray eventTimes,
             final ResizableIntArray xCoords, final ResizableIntArray yCoords) {

java/src/com/android/inputmethod/keyboard/internal/PreviewPlacerView.java

@@ -205,7 +205,7 @@ public class PreviewPlacerView extends RelativeLayout {
                     mGesturePreviewTrails.put(tracker.mPointerId, trail);
                 }
             }
-            trail.addStroke(tracker.getGestureStrokeWithPreviewTrail(), tracker.getDownTime());
+            trail.addStroke(tracker.getGestureStrokeWithPreviewPoints(), tracker.getDownTime());
         }
 
         // TODO: Should narrow the invalidate region.