Android example source code file (TouchPaint.java)

This example Android source code file (TouchPaint.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, bitmap, canvas, clear_id, drawing, fade_delay, fade_id, fade_msg, graphics, graphicsactivity, handler, max_fade_steps, myview, os, override, paint, rect, trackball_scale, ui, view

The TouchPaint.java Android example source code

/*
 * Copyright (C) 2007 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.example.android.apis.graphics;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;

//Need the following import to get access to the app resources, since this
//class is in a sub-package.


/**
 * Demonstrates the handling of touch screen and trackball events to
 * implement a simple painting app.
 */
public class TouchPaint extends GraphicsActivity {
    /** Used as a pulse to gradually fade the contents of the window. */
    private static final int FADE_MSG = 1;
    
    /** Menu ID for the command to clear the window. */
    private static final int CLEAR_ID = Menu.FIRST;
    /** Menu ID for the command to toggle fading. */
    private static final int FADE_ID = Menu.FIRST+1;
    
    /** How often to fade the contents of the window (in ms). */
    private static final int FADE_DELAY = 100;
    
    /** The view responsible for drawing the window. */
    MyView mView;
    /** Is fading mode enabled? */
    boolean mFading;
    
    @Override protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        // Create and attach the view that is responsible for painting.
        mView = new MyView(this);
        setContentView(mView);
        mView.requestFocus();
        
        // Restore the fading option if we are being thawed from a
        // previously saved state.  Note that we are not currently remembering
        // the contents of the bitmap.
        mFading = savedInstanceState != null ? savedInstanceState.getBoolean("fading", true) : true;
    }
    
    @Override public boolean onCreateOptionsMenu(Menu menu) {
        menu.add(0, CLEAR_ID, 0, "Clear");
        menu.add(0, FADE_ID, 0, "Fade").setCheckable(true);
        return super.onCreateOptionsMenu(menu);
    }

    @Override public boolean onPrepareOptionsMenu(Menu menu) {
        menu.findItem(FADE_ID).setChecked(mFading);
        return super.onPrepareOptionsMenu(menu);
    }

    @Override public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case CLEAR_ID:
                mView.clear();
                return true;
            case FADE_ID:
                mFading = !mFading;
                if (mFading) {
                    startFading();
                } else {
                    stopFading();
                }
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    @Override protected void onResume() {
        super.onResume();
        // If fading mode is enabled, then as long as we are resumed we want
        // to run pulse to fade the contents.
        if (mFading) {
            startFading();
        }
    }

    @Override protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        // Save away the fading state to restore if needed later.  Note that
        // we do not currently save the contents of the display.
        outState.putBoolean("fading", mFading);
    }

    @Override protected void onPause() {
        super.onPause();
        // Make sure to never run the fading pulse while we are paused or
        // stopped.
        stopFading();
    }

    /**
     * Start up the pulse to fade the screen, clearing any existing pulse to
     * ensure that we don't have multiple pulses running at a time.
     */
    void startFading() {
        mHandler.removeMessages(FADE_MSG);
        mHandler.sendMessageDelayed(
                mHandler.obtainMessage(FADE_MSG), FADE_DELAY);
    }
    
    /**
     * Stop the pulse to fade the screen.
     */
    void stopFading() {
        mHandler.removeMessages(FADE_MSG);
    }
    
    private Handler mHandler = new Handler() {
        @Override public void handleMessage(Message msg) {
            switch (msg.what) {
                // Upon receiving the fade pulse, we have the view perform a
                // fade and then enqueue a new message to pulse at the desired
                // next time.
                case FADE_MSG: {
                    mView.fade();
                    mHandler.sendMessageDelayed(
                            mHandler.obtainMessage(FADE_MSG), FADE_DELAY);
                    break;
                }
                default:
                    super.handleMessage(msg);
            }
        }
    };
    
    public class MyView extends View {
        private static final int FADE_ALPHA = 0x06;
        private static final int MAX_FADE_STEPS = 256/FADE_ALPHA + 4;
        private static final int TRACKBALL_SCALE = 10;

        private Bitmap mBitmap;
        private Canvas mCanvas;
        private final Rect mRect = new Rect();
        private final Paint mPaint;
        private final Paint mFadePaint;
        private float mCurX;
        private float mCurY;
        private int mFadeSteps = MAX_FADE_STEPS;
        
        public MyView(Context c) {
            super(c);
            setFocusable(true);
            mPaint = new Paint();
            mPaint.setAntiAlias(true);
            mPaint.setARGB(255, 255, 255, 255);
            mFadePaint = new Paint();
            mFadePaint.setDither(true);
            mFadePaint.setARGB(FADE_ALPHA, 0, 0, 0);
        }

        public void clear() {
            if (mCanvas != null) {
                mPaint.setARGB(0xff, 0, 0, 0);
                mCanvas.drawPaint(mPaint);
                invalidate();
                mFadeSteps = MAX_FADE_STEPS;
            }
        }
        
        public void fade() {
            if (mCanvas != null && mFadeSteps < MAX_FADE_STEPS) {
                mCanvas.drawPaint(mFadePaint);
                invalidate();
                mFadeSteps++;
            }
        }
        
        @Override protected void onSizeChanged(int w, int h, int oldw,
                int oldh) {
            int curW = mBitmap != null ? mBitmap.getWidth() : 0;
            int curH = mBitmap != null ? mBitmap.getHeight() : 0;
            if (curW >= w && curH >= h) {
                return;
            }
            
            if (curW < w) curW = w;
            if (curH < h) curH = h;
            
            Bitmap newBitmap = Bitmap.createBitmap(curW, curH,
                                                   Bitmap.Config.RGB_565);
            Canvas newCanvas = new Canvas();
            newCanvas.setBitmap(newBitmap);
            if (mBitmap != null) {
                newCanvas.drawBitmap(mBitmap, 0, 0, null);
            }
            mBitmap = newBitmap;
            mCanvas = newCanvas;
            mFadeSteps = MAX_FADE_STEPS;
        }
        
        @Override protected void onDraw(Canvas canvas) {
            if (mBitmap != null) {
                canvas.drawBitmap(mBitmap, 0, 0, null);
            }
        }

        @Override public boolean onTrackballEvent(MotionEvent event) {
            int N = event.getHistorySize();
            final float scaleX = event.getXPrecision() * TRACKBALL_SCALE;
            final float scaleY = event.getYPrecision() * TRACKBALL_SCALE;
            for (int i=0; i<N; i++) {
                //Log.i("TouchPaint", "Intermediate trackball #" + i
                //        + ": x=" + event.getHistoricalX(i)
                //        + ", y=" + event.getHistoricalY(i));
                mCurX += event.getHistoricalX(i) * scaleX;
                mCurY += event.getHistoricalY(i) * scaleY;
                drawPoint(mCurX, mCurY, 1.0f, 16.0f);
            }
            //Log.i("TouchPaint", "Trackball: x=" + event.getX()
            //        + ", y=" + event.getY());
            mCurX += event.getX() * scaleX;
            mCurY += event.getY() * scaleY;
            drawPoint(mCurX, mCurY, 1.0f, 16.0f);
            return true;
        }
        
        @Override public boolean onTouchEvent(MotionEvent event) {
            int action = event.getActionMasked();
            if (action != MotionEvent.ACTION_UP && action != MotionEvent.ACTION_CANCEL) {
                int N = event.getHistorySize();
                int P = event.getPointerCount();
                for (int i = 0; i < N; i++) {
                    for (int j = 0; j < P; j++) {
                        mCurX = event.getHistoricalX(j, i);
                        mCurY = event.getHistoricalY(j, i);
                        drawPoint(mCurX, mCurY,
                                event.getHistoricalPressure(j, i),
                                event.getHistoricalTouchMajor(j, i));
                    }
                }
                for (int j = 0; j < P; j++) {
                    mCurX = event.getX(j);
                    mCurY = event.getY(j);
                    drawPoint(mCurX, mCurY, event.getPressure(j), event.getTouchMajor(j));
                }
            }
            return true;
        }
        
        private void drawPoint(float x, float y, float pressure, float width) {
            //Log.i("TouchPaint", "Drawing: " + x + "x" + y + " p="
            //        + pressure + " width=" + width);
            if (width < 1) width = 1;
            if (mBitmap != null) {
                float radius = width / 2;
                int pressureLevel = (int)(pressure * 255);
                mPaint.setARGB(pressureLevel, 255, 255, 255);
                mCanvas.drawCircle(x, y, radius, mPaint);
                mRect.set((int) (x - radius - 2), (int) (y - radius - 2),
                        (int) (x + radius + 2), (int) (y + radius + 2));
                invalidate(mRect);
            }
            mFadeSteps = 0;
        }
    }
}