core/java/com/android/internal/widget/PointerLocationView.java

/*
 * Copyright (C) 2010 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.internal.widget;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RectF;
import android.graphics.Paint.FontMetricsInt;
import android.util.Log;
import android.view.InputDevice;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.MotionEvent.PointerCoords;

import java.util.ArrayList;

public class PointerLocationView extends View {
    private static final String TAG = "Pointer";
    
    public static class PointerState {
        // Trace of previous points.
        private float[] mTraceX = new float[32];
        private float[] mTraceY = new float[32];
        private int mTraceCount;
        
        // True if the pointer is down.
        private boolean mCurDown;
        
        // Most recent coordinates.
        private PointerCoords mCoords = new PointerCoords();
        
        // Most recent velocity.
        private float mXVelocity;
        private float mYVelocity;
        
        public void clearTrace() {
            mTraceCount = 0;
        }
        
        public void addTrace(float x, float y) {
            int traceCapacity = mTraceX.length;
            if (mTraceCount == traceCapacity) {
                traceCapacity *= 2;
                float[] newTraceX = new float[traceCapacity];
                System.arraycopy(mTraceX, 0, newTraceX, 0, mTraceCount);
                mTraceX = newTraceX;
                
                float[] newTraceY = new float[traceCapacity];
                System.arraycopy(mTraceY, 0, newTraceY, 0, mTraceCount);
                mTraceY = newTraceY;
            }
            
            mTraceX[mTraceCount] = x;
            mTraceY[mTraceCount] = y;
            mTraceCount += 1;
        }
    }

    private final ViewConfiguration mVC;
    private final Paint mTextPaint;
    private final Paint mTextBackgroundPaint;
    private final Paint mTextLevelPaint;
    private final Paint mPaint;
    private final Paint mTargetPaint;
    private final Paint mPathPaint;
    private final FontMetricsInt mTextMetrics = new FontMetricsInt();
    private int mHeaderBottom;
    private boolean mCurDown;
    private int mCurNumPointers;
    private int mMaxNumPointers;
    private int mActivePointerId;
    private final ArrayList<PointerState> mPointers = new ArrayList<PointerState>();
    private final PointerCoords mHoverCoords = new PointerCoords();
    
    private final VelocityTracker mVelocity;
    
    private final FasterStringBuilder mText = new FasterStringBuilder();
    
    private boolean mPrintCoords = true;
    
    public PointerLocationView(Context c) {
        super(c);
        setFocusableInTouchMode(true);

        mVC = ViewConfiguration.get(c);
        mTextPaint = new Paint();
        mTextPaint.setAntiAlias(true);
        mTextPaint.setTextSize(10
                * getResources().getDisplayMetrics().density);
        mTextPaint.setARGB(255, 0, 0, 0);
        mTextBackgroundPaint = new Paint();
        mTextBackgroundPaint.setAntiAlias(false);
        mTextBackgroundPaint.setARGB(128, 255, 255, 255);
        mTextLevelPaint = new Paint();
        mTextLevelPaint.setAntiAlias(false);
        mTextLevelPaint.setARGB(192, 255, 0, 0);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setARGB(255, 255, 255, 255);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(2);
        mTargetPaint = new Paint();
        mTargetPaint.setAntiAlias(false);
        mTargetPaint.setARGB(255, 0, 0, 192);
        mPathPaint = new Paint();
        mPathPaint.setAntiAlias(false);
        mPathPaint.setARGB(255, 0, 96, 255);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(1);
        
        PointerState ps = new PointerState();
        mPointers.add(ps);
        mActivePointerId = 0;
        
        mVelocity = VelocityTracker.obtain();
        
        logInputDeviceCapabilities();
    }
    
    private void logInputDeviceCapabilities() {
        int[] deviceIds = InputDevice.getDeviceIds();
        for (int i = 0; i < deviceIds.length; i++) {
            InputDevice device = InputDevice.getDevice(deviceIds[i]);
            if (device != null) {
                Log.i(TAG, device.toString());
            }
        }
    }

    public void setPrintCoords(boolean state) {
        mPrintCoords = state;
    }
    
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        mTextPaint.getFontMetricsInt(mTextMetrics);
        mHeaderBottom = -mTextMetrics.ascent+mTextMetrics.descent+2;
        if (false) {
            Log.i("foo", "Metrics: ascent=" + mTextMetrics.ascent
                    + " descent=" + mTextMetrics.descent
                    + " leading=" + mTextMetrics.leading
                    + " top=" + mTextMetrics.top
                    + " bottom=" + mTextMetrics.bottom);
        }
    }
    
    // Draw an oval.  When angle is 0 radians, orients the major axis vertically,
    // angles less than or greater than 0 radians rotate the major axis left or right.
    private RectF mReusableOvalRect = new RectF();
    private void drawOval(Canvas canvas, float x, float y, float major, float minor,
            float angle, Paint paint) {
        canvas.save(Canvas.MATRIX_SAVE_FLAG);
        canvas.rotate((float) (angle * 180 / Math.PI), x, y);
        mReusableOvalRect.left = x - minor / 2;
        mReusableOvalRect.right = x + minor / 2;
        mReusableOvalRect.top = y - major / 2;
        mReusableOvalRect.bottom = y + major / 2;
        canvas.drawOval(mReusableOvalRect, paint);
        canvas.restore();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        synchronized (mPointers) {
            final int w = getWidth();
            final int itemW = w/7;
            final int base = -mTextMetrics.ascent+1;
            final int bottom = mHeaderBottom;
            
            final int NP = mPointers.size();
            
            // Labels
            if (mActivePointerId >= 0) {
                final PointerState ps = mPointers.get(mActivePointerId);
                
                canvas.drawRect(0, 0, itemW-1, bottom,mTextBackgroundPaint);
                canvas.drawText(mText.clear()
                        .append("P: ").append(mCurNumPointers)
                        .append(" / ").append(mMaxNumPointers)
                        .toString(), 1, base, mTextPaint);

                final int N = ps.mTraceCount;
                if ((mCurDown && ps.mCurDown) || N == 0) {
                    canvas.drawRect(itemW, 0, (itemW * 2) - 1, bottom, mTextBackgroundPaint);
                    canvas.drawText(mText.clear()
                            .append("X: ").append(ps.mCoords.x, 1)
                            .toString(), 1 + itemW, base, mTextPaint);
                    canvas.drawRect(itemW * 2, 0, (itemW * 3) - 1, bottom, mTextBackgroundPaint);
                    canvas.drawText(mText.clear()
                            .append("Y: ").append(ps.mCoords.y, 1)
                            .toString(), 1 + itemW * 2, base, mTextPaint);
                } else {
                    float dx = ps.mTraceX[N - 1] - ps.mTraceX[0];
                    float dy = ps.mTraceY[N - 1] - ps.mTraceY[0];
                    canvas.drawRect(itemW, 0, (itemW * 2) - 1, bottom,
                            Math.abs(dx) < mVC.getScaledTouchSlop()
                            ? mTextBackgroundPaint : mTextLevelPaint);
                    canvas.drawText(mText.clear()
                            .append("dX: ").append(dx, 1)
                            .toString(), 1 + itemW, base, mTextPaint);
                    canvas.drawRect(itemW * 2, 0, (itemW * 3) - 1, bottom,
                            Math.abs(dy) < mVC.getScaledTouchSlop()
                            ? mTextBackgroundPaint : mTextLevelPaint);
                    canvas.drawText(mText.clear()
                            .append("dY: ").append(dy, 1)
                            .toString(), 1 + itemW * 2, base, mTextPaint);
                }
                
                canvas.drawRect(itemW * 3, 0, (itemW * 4) - 1, bottom, mTextBackgroundPaint);
                canvas.drawText(mText.clear()
                        .append("Xv: ").append(ps.mXVelocity, 3)
                        .toString(), 1 + itemW * 3, base, mTextPaint);
                
                canvas.drawRect(itemW * 4, 0, (itemW * 5) - 1, bottom, mTextBackgroundPaint);
                canvas.drawText(mText.clear()
                        .append("Yv: ").append(ps.mYVelocity, 3)
                        .toString(), 1 + itemW * 4, base, mTextPaint);
                
                canvas.drawRect(itemW * 5, 0, (itemW * 6) - 1, bottom, mTextBackgroundPaint);
                canvas.drawRect(itemW * 5, 0, (itemW * 5) + (ps.mCoords.pressure * itemW) - 1,
                        bottom, mTextLevelPaint);
                canvas.drawText(mText.clear()
                        .append("Prs: ").append(ps.mCoords.pressure, 2)
                        .toString(), 1 + itemW * 5, base, mTextPaint);
                
                canvas.drawRect(itemW * 6, 0, w, bottom, mTextBackgroundPaint);
                canvas.drawRect(itemW * 6, 0, (itemW * 6) + (ps.mCoords.size * itemW) - 1,
                        bottom, mTextLevelPaint);
                canvas.drawText(mText.clear()
                        .append("Size: ").append(ps.mCoords.size, 2)
                        .toString(), 1 + itemW * 6, base, mTextPaint);
            }
            
            // Pointer trace.
            for (int p = 0; p < NP; p++) {
                final PointerState ps = mPointers.get(p);
                
                // Draw path.
                final int N = ps.mTraceCount;
                float lastX = 0, lastY = 0;
                boolean haveLast = false;
                boolean drawn = false;
                mPaint.setARGB(255, 128, 255, 255);
                for (int i=0; i < N; i++) {
                    float x = ps.mTraceX[i];
                    float y = ps.mTraceY[i];
                    if (Float.isNaN(x)) {
                        haveLast = false;
                        continue;
                    }
                    if (haveLast) {
                        canvas.drawLine(lastX, lastY, x, y, mPathPaint);
                        canvas.drawPoint(lastX, lastY, mPaint);
                        drawn = true;
                    }
                    lastX = x;
                    lastY = y;
                    haveLast = true;
                }
                
                // Draw velocity vector.
                if (drawn) {
                    mPaint.setARGB(255, 255, 64, 128);
                    float xVel = ps.mXVelocity * (1000 / 60);
                    float yVel = ps.mYVelocity * (1000 / 60);
                    canvas.drawLine(lastX, lastY, lastX + xVel, lastY + yVel, mPaint);
                }
                
                if (mCurDown && ps.mCurDown) {
                    // Draw crosshairs.
                    canvas.drawLine(0, ps.mCoords.y, getWidth(), ps.mCoords.y, mTargetPaint);
                    canvas.drawLine(ps.mCoords.x, 0, ps.mCoords.x, getHeight(), mTargetPaint);
                    
                    // Draw current point.
                    int pressureLevel = (int)(ps.mCoords.pressure * 255);
                    mPaint.setARGB(255, pressureLevel, 255, 255 - pressureLevel);
                    canvas.drawPoint(ps.mCoords.x, ps.mCoords.y, mPaint);
                    
                    // Draw current touch ellipse.
                    mPaint.setARGB(255, pressureLevel, 255 - pressureLevel, 128);
                    drawOval(canvas, ps.mCoords.x, ps.mCoords.y, ps.mCoords.touchMajor,
                            ps.mCoords.touchMinor, ps.mCoords.orientation, mPaint);
                    
                    // Draw current tool ellipse.
                    mPaint.setARGB(255, pressureLevel, 128, 255 - pressureLevel);
                    drawOval(canvas, ps.mCoords.x, ps.mCoords.y, ps.mCoords.toolMajor,
                            ps.mCoords.toolMinor, ps.mCoords.orientation, mPaint);

                    // Draw the orientation arrow.
                    mPaint.setARGB(255, pressureLevel, 255, 0);
                    float orientationVectorX = (float) (Math.sin(-ps.mCoords.orientation)
                            * ps.mCoords.toolMajor * 0.7);
                    float orientationVectorY = (float) (Math.cos(-ps.mCoords.orientation)
                            * ps.mCoords.toolMajor * 0.7);
                    canvas.drawLine(
                            ps.mCoords.x - orientationVectorX, ps.mCoords.y - orientationVectorY,
                            ps.mCoords.x + orientationVectorX, ps.mCoords.y + orientationVectorY,
                            mPaint);
                }
            }
        }
    }
    
    private void logPointerCoords(int action, int index, MotionEvent.PointerCoords coords, int id) {
        final String prefix;
        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                prefix = "DOWN";
                break;
            case MotionEvent.ACTION_UP:
                prefix = "UP";
                break;
            case MotionEvent.ACTION_MOVE:
                prefix = "MOVE";
                break;
            case MotionEvent.ACTION_CANCEL:
                prefix = "CANCEL";
                break;
            case MotionEvent.ACTION_OUTSIDE:
                prefix = "OUTSIDE";
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                if (index == ((action & MotionEvent.ACTION_POINTER_INDEX_MASK)
                        >> MotionEvent.ACTION_POINTER_INDEX_SHIFT)) {
                    prefix = "DOWN";
                } else {
                    prefix = "MOVE";
                }
                break;
            case MotionEvent.ACTION_POINTER_UP:
                if (index == ((action & MotionEvent.ACTION_POINTER_INDEX_MASK)
                        >> MotionEvent.ACTION_POINTER_INDEX_SHIFT)) {
                    prefix = "UP";
                } else {
                    prefix = "MOVE";
                }
                break;
            case MotionEvent.ACTION_HOVER_MOVE:
                prefix = "HOVER MOVE";
                break;
            case MotionEvent.ACTION_HOVER_ENTER:
                prefix = "HOVER ENTER";
                break;
            case MotionEvent.ACTION_HOVER_EXIT:
                prefix = "HOVER EXIT";
                break;
            case MotionEvent.ACTION_SCROLL:
                prefix = "SCROLL";
                break;
            default:
                prefix = Integer.toString(action);
                break;
        }

        Log.i(TAG, mText.clear()
                .append("Pointer ").append(id + 1)
                .append(": ")
                .append(prefix)
                .append(" (").append(coords.x, 3).append(", ").append(coords.y, 3)
                .append(") Pressure=").append(coords.pressure, 3)
                .append(" Size=").append(coords.size, 3)
                .append(" TouchMajor=").append(coords.touchMajor, 3)
                .append(" TouchMinor=").append(coords.touchMinor, 3)
                .append(" ToolMajor=").append(coords.toolMajor, 3)
                .append(" ToolMinor=").append(coords.toolMinor, 3)
                .append(" Orientation=").append((float)(coords.orientation * 180 / Math.PI), 1)
                .append("deg")
                .append(" VScroll=").append(coords.getAxisValue(MotionEvent.AXIS_VSCROLL), 1)
                .append(" HScroll=").append(coords.getAxisValue(MotionEvent.AXIS_HSCROLL), 1)
                .toString());
    }

    public void addPointerEvent(MotionEvent event) {
        synchronized (mPointers) {
            int action = event.getAction();
            
            //Log.i(TAG, "Motion: action=0x" + Integer.toHexString(action)
            //        + " pointers=" + event.getPointerCount());
            
            int NP = mPointers.size();
            
            //mRect.set(0, 0, getWidth(), mHeaderBottom+1);
            //invalidate(mRect);
            //if (mCurDown) {
            //    mRect.set(mCurX-mCurWidth-3, mCurY-mCurWidth-3,
            //            mCurX+mCurWidth+3, mCurY+mCurWidth+3);
            //} else {
            //    mRect.setEmpty();
            //}
            if (action == MotionEvent.ACTION_DOWN
                    || (action & MotionEvent.ACTION_MASK) == MotionEvent.ACTION_POINTER_DOWN) {
                final int index = (action & MotionEvent.ACTION_POINTER_INDEX_MASK)
                        >> MotionEvent.ACTION_POINTER_INDEX_SHIFT; // will be 0 for down
                if (action == MotionEvent.ACTION_DOWN) {
                    for (int p=0; p<NP; p++) {
                        final PointerState ps = mPointers.get(p);
                        ps.clearTrace();
                        ps.mCurDown = false;
                    }
                    mCurDown = true;
                    mCurNumPointers = 0;
                    mMaxNumPointers = 0;
                    mVelocity.clear();
                }

                mCurNumPointers += 1;
                if (mMaxNumPointers < mCurNumPointers) {
                    mMaxNumPointers = mCurNumPointers;
                }

                final int id = event.getPointerId(index);
                while (NP <= id) {
                    PointerState ps = new PointerState();
                    mPointers.add(ps);
                    NP++;
                }
                
                if (mActivePointerId < 0 ||
                        !mPointers.get(mActivePointerId).mCurDown) {
                    mActivePointerId = id;
                }
                
                final PointerState ps = mPointers.get(id);
                ps.mCurDown = true;
            }

            final int NI = event.getPointerCount();

            mVelocity.addMovement(event);
            mVelocity.computeCurrentVelocity(1);

            final int N = event.getHistorySize();
            for (int historyPos = 0; historyPos < N; historyPos++) {
                for (int i = 0; i < NI; i++) {
                    final int id = event.getPointerId(i);
                    final PointerState ps = mCurDown ? mPointers.get(id) : null;
                    final PointerCoords coords = ps != null ? ps.mCoords : mHoverCoords;
                    event.getHistoricalPointerCoords(i, historyPos, coords);
                    if (mPrintCoords) {
                        logPointerCoords(action, i, coords, id);
                    }
                    if (ps != null) {
                        ps.addTrace(coords.x, coords.y);
                    }
                }
            }
            for (int i = 0; i < NI; i++) {
                final int id = event.getPointerId(i);
                final PointerState ps = mCurDown ? mPointers.get(id) : null;
                final PointerCoords coords = ps != null ? ps.mCoords : mHoverCoords;
                event.getPointerCoords(i, coords);
                if (mPrintCoords) {
                    logPointerCoords(action, i, coords, id);
                }
                if (ps != null) {
                    ps.addTrace(coords.x, coords.y);
                    ps.mXVelocity = mVelocity.getXVelocity(id);
                    ps.mYVelocity = mVelocity.getYVelocity(id);
                }
            }

            if (action == MotionEvent.ACTION_UP
                    || action == MotionEvent.ACTION_CANCEL
                    || (action & MotionEvent.ACTION_MASK) == MotionEvent.ACTION_POINTER_UP) {
                final int index = (action & MotionEvent.ACTION_POINTER_INDEX_MASK)
                        >> MotionEvent.ACTION_POINTER_INDEX_SHIFT; // will be 0 for UP
                
                final int id = event.getPointerId(index);
                final PointerState ps = mPointers.get(id);
                ps.mCurDown = false;
                
                if (action == MotionEvent.ACTION_UP
                        || action == MotionEvent.ACTION_CANCEL) {
                    mCurDown = false;
                    mCurNumPointers = 0;
                } else {
                    mCurNumPointers -= 1;
                    if (mActivePointerId == id) {
                        mActivePointerId = event.getPointerId(index == 0 ? 1 : 0);
                    }
                    ps.addTrace(Float.NaN, Float.NaN);
                }
            }
            
            //if (mCurDown) {
            //    mRect.union(mCurX-mCurWidth-3, mCurY-mCurWidth-3,
            //            mCurX+mCurWidth+3, mCurY+mCurWidth+3);
            //}
            //invalidate(mRect);
            postInvalidate();
        }
    }
    
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        addPointerEvent(event);

        if (event.getAction() == MotionEvent.ACTION_DOWN && !isFocused()) {
            requestFocus();
        }
        return true;
    }

    @Override
    public boolean onGenericMotionEvent(MotionEvent event) {
        final int source = event.getSource();
        if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {
            addPointerEvent(event);
        } else if ((source & InputDevice.SOURCE_CLASS_JOYSTICK) != 0) {
            Log.i(TAG, "Joystick: " + event);
        } else if ((source & InputDevice.SOURCE_CLASS_POSITION) != 0) {
            Log.i(TAG, "Position: " + event);
        } else {
            Log.i(TAG, "Generic: " + event);
        }
        return true;
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (shouldLogKey(keyCode)) {
            final int repeatCount = event.getRepeatCount();
            if (repeatCount == 0) {
                Log.i(TAG, "Key Down: " + event);
            } else {
                Log.i(TAG, "Key Repeat #" + repeatCount + ": " + event);
            }
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (shouldLogKey(keyCode)) {
            Log.i(TAG, "Key Up: " + event);
            return true;
        }
        return super.onKeyUp(keyCode, event);
    }

    private static boolean shouldLogKey(int keyCode) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_DPAD_UP:
            case KeyEvent.KEYCODE_DPAD_DOWN:
            case KeyEvent.KEYCODE_DPAD_LEFT:
            case KeyEvent.KEYCODE_DPAD_RIGHT:
            case KeyEvent.KEYCODE_DPAD_CENTER:
                return true;
            default:
                return KeyEvent.isGamepadButton(keyCode)
                    || KeyEvent.isModifierKey(keyCode);
        }
    }

    @Override
    public boolean onTrackballEvent(MotionEvent event) {
        Log.i(TAG, "Trackball: " + event);
        return true;
    }
    
    // HACK
    // A quick and dirty string builder implementation optimized for GC.
    // Using String.format causes the application grind to a halt when
    // more than a couple of pointers are down due to the number of
    // temporary objects allocated while formatting strings for drawing or logging.
    private static final class FasterStringBuilder {
        private char[] mChars;
        private int mLength;
        
        public FasterStringBuilder() {
            mChars = new char[64];
        }
        
        public FasterStringBuilder clear() {
            mLength = 0;
            return this;
        }
        
        public FasterStringBuilder append(String value) {
            final int valueLength = value.length();
            final int index = reserve(valueLength);
            value.getChars(0, valueLength, mChars, index);
            mLength += valueLength;
            return this;
        }
        
        public FasterStringBuilder append(int value) {
            return append(value, 0);
        }
        
        public FasterStringBuilder append(int value, int zeroPadWidth) {
            final boolean negative = value < 0;
            if (negative) {
                value = - value;
                if (value < 0) {
                    append("-2147483648");
                    return this;
                }
            }
            
            int index = reserve(11);
            final char[] chars = mChars;
            
            if (value == 0) {
                chars[index++] = '0';
                mLength += 1;
                return this;
            }
            
            if (negative) {
                chars[index++] = '-';
            }

            int divisor = 1000000000;
            int numberWidth = 10;
            while (value < divisor) {
                divisor /= 10;
                numberWidth -= 1;
                if (numberWidth < zeroPadWidth) {
                    chars[index++] = '0';
                }
            }
            
            do {
                int digit = value / divisor;
                value -= digit * divisor;
                divisor /= 10;
                chars[index++] = (char) (digit + '0');
            } while (divisor != 0);
            
            mLength = index;
            return this;
        }
        
        public FasterStringBuilder append(float value, int precision) {
            int scale = 1;
            for (int i = 0; i < precision; i++) {
                scale *= 10;
            }
            value = (float) (Math.rint(value * scale) / scale);
            
            append((int) value);

            if (precision != 0) {
                append(".");
                value = Math.abs(value);
                value -= Math.floor(value);
                append((int) (value * scale), precision);
            }
            
            return this;
        }
        
        @Override
        public String toString() {
            return new String(mChars, 0, mLength);
        }
        
        private int reserve(int length) {
            final int oldLength = mLength;
            final int newLength = mLength + length;
            final char[] oldChars = mChars;
            final int oldCapacity = oldChars.length;
            if (newLength > oldCapacity) {
                final int newCapacity = oldCapacity * 2;
                final char[] newChars = new char[newCapacity];
                System.arraycopy(oldChars, 0, newChars, 0, oldLength);
                mChars = newChars;
            }
            return oldLength;
        }
    }
}