Use offscreen bitmap buffer to draw gesture preview trail

Bug: 7042741
Change-Id: Ie3d7054e786938dc501c7aa2ffc96b5924a7967b

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

@@ -182,7 +182,7 @@ public class KeyboardView extends View implements PointerTracker.DrawingProxy {
     private final Region mClipRegion = new Region();
     private Bitmap mOffscreenBuffer;
     /** The canvas for the above mutable keyboard bitmap */
-    private Canvas mOffscreenCanvas;
+    private final Canvas mOffscreenCanvas = new Canvas();
     private final Paint mPaint = new Paint();
     private final Paint.FontMetrics mFontMetrics = new Paint.FontMetrics();
     // This sparse array caches key label text height in pixel indexed by key label text size.
@@ -365,7 +365,8 @@ public class KeyboardView extends View implements PointerTracker.DrawingProxy {
         if (bufferNeedsUpdates || mOffscreenBuffer == null) {
             if (maybeAllocateOffscreenBuffer()) {
                 mInvalidateAllKeys = true;
-                maybeCreateOffscreenCanvas();
+                // TODO: Stop using the offscreen canvas even when in software rendering
+                mOffscreenCanvas.setBitmap(mOffscreenBuffer);
             }
             onDrawKeyboard(mOffscreenCanvas);
         }
@@ -394,15 +395,6 @@ public class KeyboardView extends View implements PointerTracker.DrawingProxy {
         }
     }
 
-    private void maybeCreateOffscreenCanvas() {
-        // TODO: Stop using the offscreen canvas even when in software rendering
-        if (mOffscreenCanvas != null) {
-            mOffscreenCanvas.setBitmap(mOffscreenBuffer);
-        } else {
-            mOffscreenCanvas = new Canvas(mOffscreenBuffer);
-        }
-    }
-
     private void onDrawKeyboard(final Canvas canvas) {
         if (mKeyboard == null) return;
 

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

@@ -17,9 +17,7 @@ package com.android.inputmethod.keyboard.internal;
 import android.content.res.TypedArray;
 import android.graphics.Canvas;
 import android.graphics.Paint;
-import android.graphics.PorterDuff;
+import android.graphics.Rect;
-import android.graphics.PorterDuffXfermode;
-import android.graphics.Xfermode;
 import android.os.SystemClock;
 
 import com.android.inputmethod.latin.Constants;
@@ -118,17 +116,16 @@ final class GesturePreviewTrail {
                 / params.mTrailLingerDuration, 0.0f);
     }
 
-    private final static Xfermode PORTER_DUFF_MODE_SRC =
-            new PorterDuffXfermode(PorterDuff.Mode.SRC);
-
     /**
      * Draw gesture preview trail
      * @param canvas The canvas to draw the gesture preview trail
      * @param paint The paint object to be used to draw the gesture preview trail
+     * @param outBoundsRect the bounding box of this gesture trail drawing
      * @param params The drawing parameters of gesture preview trail
      * @return true if some gesture preview trails remain to be drawn
      */
-    public boolean drawGestureTrail(final Canvas canvas, final Paint paint, final Params params) {
+    public boolean drawGestureTrail(final Canvas canvas, final Paint paint,
+            final Rect outBoundsRect, final Params params) {
         final int trailSize = mEventTimes.getLength();
         if (trailSize == 0) {
             return false;
@@ -149,12 +146,14 @@ final class GesturePreviewTrail {
         mTrailStartIndex = startIndex;
 
         if (startIndex < trailSize) {
-            int lastX = getXCoordValue(xCoords[startIndex]);
-            int lastY = yCoords[startIndex];
             paint.setColor(params.mTrailColor);
             paint.setStyle(Paint.Style.STROKE);
             paint.setStrokeCap(Paint.Cap.ROUND);
-            paint.setXfermode(PORTER_DUFF_MODE_SRC);
+            int lastX = getXCoordValue(xCoords[startIndex]);
+            int lastY = yCoords[startIndex];
+            float maxWidth = getWidth(sinceDown - eventTimes[startIndex], params);
+            // Initialize bounds rectangle.
+            outBoundsRect.set(lastX, lastY, lastX, lastY);
             for (int i = startIndex + 1; i < trailSize - 1; i++) {
                 final int x = xCoords[i];
                 final int y = yCoords[i];
@@ -166,10 +165,16 @@ final class GesturePreviewTrail {
                     final float width = getWidth(elapsedTime, params);
                     paint.setStrokeWidth(width);
                     canvas.drawLine(lastX, lastY, x, y, paint);
+                    // Take union for the bounds.
+                    outBoundsRect.union(x, y);
+                    maxWidth = Math.max(maxWidth, width);
                 }
                 lastX = getXCoordValue(x);
                 lastY = y;
             }
+            // Take care of trail line width.
+            final int inset = -((int)maxWidth + 1);
+            outBoundsRect.inset(inset, inset);
         }
 
         final int newSize = trailSize - startIndex;

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

@@ -18,7 +18,9 @@ package com.android.inputmethod.keyboard.internal;
 
 import android.content.Context;
 import android.content.res.TypedArray;
+import android.graphics.Bitmap;
 import android.graphics.Canvas;
+import android.graphics.Color;
 import android.graphics.Paint;
 import android.graphics.Paint.Align;
 import android.graphics.PorterDuff;
@@ -54,6 +56,10 @@ public class PreviewPlacerView extends RelativeLayout {
     private final Params mGesturePreviewTrailParams;
     private final Paint mGesturePaint;
     private boolean mDrawsGesturePreviewTrail;
+    private Bitmap mOffscreenBuffer;
+    private final Canvas mOffscreenCanvas = new Canvas();
+    private final Rect mOffscreenDirtyRect = new Rect();
+    private final Rect mGesturePreviewTrailBoundsRect = new Rect(); // per trail
 
     private final Paint mTextPaint;
     private String mGestureFloatingPreviewText;
@@ -154,6 +160,7 @@ public class PreviewPlacerView extends RelativeLayout {
 
         final Paint gesturePaint = new Paint();
         gesturePaint.setAntiAlias(true);
+        gesturePaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
         mGesturePaint = gesturePaint;
 
         final Paint textPaint = new Paint();
@@ -198,11 +205,31 @@ public class PreviewPlacerView extends RelativeLayout {
         invalidate();
     }
 
+    @Override
+    protected void onDetachedFromWindow() {
+        if (mOffscreenBuffer != null) {
+            mOffscreenBuffer.recycle();
+            mOffscreenBuffer = null;
+        }
+    }
+
     @Override
     public void onDraw(final Canvas canvas) {
         super.onDraw(canvas);
         canvas.translate(mXOrigin, mYOrigin);
         if (mDrawsGesturePreviewTrail) {
+            if (mOffscreenBuffer == null) {
+                mOffscreenBuffer = Bitmap.createBitmap(
+                        getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
+                mOffscreenCanvas.setBitmap(mOffscreenBuffer);
+            }
+            if (!mOffscreenDirtyRect.isEmpty()) {
+                // Clear previous dirty rectangle.
+                mGesturePaint.setColor(Color.TRANSPARENT);
+                mGesturePaint.setStyle(Paint.Style.FILL);
+                mOffscreenCanvas.drawRect(mOffscreenDirtyRect, mGesturePaint);
+                mOffscreenDirtyRect.setEmpty();
+            }
             boolean needsUpdatingGesturePreviewTrail = false;
             synchronized (mGesturePreviewTrails) {
                 // Trails count == fingers count that have ever been active.
@@ -210,10 +237,18 @@ public class PreviewPlacerView extends RelativeLayout {
                 for (int index = 0; index < trailsCount; index++) {
                     final GesturePreviewTrail trail = mGesturePreviewTrails.valueAt(index);
                     needsUpdatingGesturePreviewTrail |=
-                            trail.drawGestureTrail(canvas, mGesturePaint,
+                            trail.drawGestureTrail(mOffscreenCanvas, mGesturePaint,
-                                    mGesturePreviewTrailParams);
+                                    mGesturePreviewTrailBoundsRect, mGesturePreviewTrailParams);
+                    // {@link #mGesturePreviewTrailBoundsRect} has bounding box of the trail.
+                    mOffscreenDirtyRect.union(mGesturePreviewTrailBoundsRect);
                 }
             }
+            if (!mOffscreenDirtyRect.isEmpty()) {
+                canvas.drawBitmap(mOffscreenBuffer, mOffscreenDirtyRect, mOffscreenDirtyRect,
+                        mGesturePaint);
+                // Note: Defer clearing the dirty rectangle here because we will get cleared
+                // rectangle on the canvas.
+            }
             if (needsUpdatingGesturePreviewTrail) {
                 mDrawingHandler.postUpdateGestureTrailPreview();
             }
@@ -263,7 +298,6 @@ public class PreviewPlacerView extends RelativeLayout {
         final float round = mGestureFloatingPreviewRoundRadius;
         paint.setColor(mGestureFloatingPreviewColor);
         canvas.drawRoundRect(rectangle, round, round, paint);
-
         // Paint the text preview
         paint.setColor(mGestureFloatingPreviewTextColor);
         final float textX = rectX + hPad + textWidth / 2.0f;