Objectif.
Le but est de réaliser un mini logiciel de dessin pour Android. Le code est celui de l'ancien fingerpaint pour android 1.1.
Réalisation.
MainActivity.java.
Pour dessiner on a besoin de 4 éléments : 
Le path est une courbe de bézier qui trace le bitmap.
 * 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.fingerpaint;
import android.app.*;
import android.content.Context;
import android.graphics.*;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
public class MainActivity extends Activity
 implements ColorPickerDialog.OnColorChangedListener {
 private Paint mPaint;
 private MaskFilter mEmboss;
 private MaskFilter mBlur;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(new MyView(this));
 // creation d'un objet paint
 mPaint = new Paint();
 // customization du paint
 mPaint.setAntiAlias(true);
 mPaint.setDither(true);
 mPaint.setColor(0xFFFF0000);
 mPaint.setStyle(Paint.Style.STROKE);
 mPaint.setStrokeJoin(Paint.Join.ROUND);
 mPaint.setStrokeCap(Paint.Cap.ROUND);
 mPaint.setStrokeWidth(12);
 // modification des propriétés sur la brosse
 mEmboss = new EmbossMaskFilter(new float[] { 1, 1, 1 },
 0.4f, 6, 3.5f);
 mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
 // permet d'assigner la couleur à l'objet paint
 public void colorChanged(int color) {
 mPaint.setColor(color);
 public class MyView extends View {
 private static final float MINP = 0.25f;
 private static final float MAXP = 0.75f;
 // les 4 éléments de bases pour permettre le dessin
 private Bitmap mBitmap;
 private Canvas mCanvas;
 private Path mPath;
 private Paint mBitmapPaint;
 public MyView(Context c) {
 super(c);
 // instanciation du path
 mPath = new Path();
 // instanciation du paint avec tramage à on.
 mBitmapPaint = new Paint(Paint.DITHER_FLAG);
 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
 super.onSizeChanged(w, h, oldw, oldh);
 // creation du bitmap ou objet du trait
 mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
 // instanciation du canvas
 mCanvas = new Canvas(mBitmap);
 // methode appelée dynamiquement quand on dessine
 @Override
 protected void onDraw(Canvas canvas) {
 // assignation de la couleur au canvas
 canvas.drawColor(0xFFAAAAAA);
 // assignation du bitmap au canvas
 canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
 // assignation du chemin au canvas
 canvas.drawPath(mPath, mPaint);
 private float mX, mY;
 // tolérance de la touche
 private static final float TOUCH_TOLERANCE = 4;
 // à la touche posée
 private void touch_start(float x, float y) {
 mPath.reset();
 // deplacement du path et positionnement en x,y
 mPath.moveTo(x, y);
 mX = x;
 mY = y;
 // à la touche en déplacement
 private void touch_move(float x, float y) {
 // approximation du bezier au deplacement
 float dx = Math.abs(x - mX);
 float dy = Math.abs(y - mY);
 if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
 mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
 mX = x;
 mY = y;
 // a la touche levée
 private void touch_up() {
 mPath.lineTo(mX, mY);
 // dessin du path sur l'objet paint
 mCanvas.drawPath(mPath, mPaint);
 // reset du path pour ne pas avoir le chemin précédent
 mPath.reset();
 // lancement des methodes de touch de l'écran tactile du smartphone
 @Override
 public boolean onTouchEvent(MotionEvent event) {
 // prend l'axe des X
 float x = event.getX();
 // prend l'axe des Y
 float y = event.getY();
 switch (event.getAction()) {
 case MotionEvent.ACTION_DOWN:
 touch_start(x, y);
 invalidate();
 break;
 case MotionEvent.ACTION_MOVE:
 touch_move(x, y);
 invalidate();
 break;
 case MotionEvent.ACTION_UP:
 touch_up();
 invalidate();
 break;
 return true;
 // assignation des ids du menu
 private static final int COLOR_MENU_ID = Menu.FIRST;
 private static final int EMBOSS_MENU_ID = Menu.FIRST + 1;
 private static final int BLUR_MENU_ID = Menu.FIRST + 2;
 private static final int ERASE_MENU_ID = Menu.FIRST + 3;
 private static final int SRCATOP_MENU_ID = Menu.FIRST + 4;
 // assignation des éléments du menu
 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
 super.onCreateOptionsMenu(menu);
 menu.add(0, COLOR_MENU_ID, 0, "Color").setShortcut('3', 'c');
 menu.add(0, EMBOSS_MENU_ID, 0, "Emboss").setShortcut('4', 's');
 menu.add(0, BLUR_MENU_ID, 0, "Blur").setShortcut('5', 'z');
 menu.add(0, ERASE_MENU_ID, 0, "Erase").setShortcut('5', 'z');
 menu.add(0, SRCATOP_MENU_ID, 0, "SrcATop").setShortcut('5', 'z');
 /**** Is this the mechanism to extend with filter effects?
 Intent intent = new Intent(null, getIntent().getData());
 intent.addCategory(Intent.CATEGORY_ALTERNATIVE);
 menu.addIntentOptions(
 Menu.ALTERNATIVE, 0,
 new ComponentName(this, NotesList.class),
 null, intent, 0, null);
 return true;
 @Override
 public boolean onPrepareOptionsMenu(Menu menu) {
 super.onPrepareOptionsMenu(menu);
 return true;
 // événements lancés selon les éléments du menu appelés
 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
 mPaint.setXfermode(null);
 mPaint.setAlpha(0xFF);
 switch (item.getItemId()) {
 case COLOR_MENU_ID:
 // ouverture d'un colorpicker
 new ColorPickerDialog(this, this, mPaint.getColor()).show();
 return true;
 case EMBOSS_MENU_ID:
 // application d'un filtre emboss sur les traits de la brosse
 if (mPaint.getMaskFilter() != mEmboss) {
 mPaint.setMaskFilter(mEmboss);
 } else {
 mPaint.setMaskFilter(null);
 return true;
 case BLUR_MENU_ID:
 // application d'un filtre blur sur les traits de la brosse
 if (mPaint.getMaskFilter() != mBlur) {
 mPaint.setMaskFilter(mBlur);
 } else {
 mPaint.setMaskFilter(null);
 return true;
 case ERASE_MENU_ID:
 // effacement du contenu de l'objet paint
 mPaint.setXfermode(new PorterDuffXfermode(
 PorterDuff.Mode.CLEAR));
 return true;
 case SRCATOP_MENU_ID:
 mPaint.setXfermode(new PorterDuffXfermode(
 PorterDuff.Mode.SRC_ATOP));
 mPaint.setAlpha(0x80);
 return true;
 return super.onOptionsItemSelected(item);
ColorPickerDialog.java.
package com.example.fingerpaint;
import android.os.Bundle;
import android.app.Dialog;
import android.content.Context;
import android.graphics.*;
import android.view.MotionEvent;
import android.view.View;
 public class ColorPickerDialog extends Dialog {
 public interface OnColorChangedListener {
 void colorChanged(int color);
 private OnColorChangedListener mListener;
 private int mInitialColor;
 private static class ColorPickerView extends View {
 private Paint mPaint;
 private Paint mCenterPaint;
 private final int[] mColors;
 private OnColorChangedListener mListener;
 ColorPickerView(Context c, OnColorChangedListener l, int color) {
 super(c);
 mListener = l;
 mColors = new int[] {
 0xFFFF0000, 0xFFFF00FF, 0xFF0000FF, 0xFF00FFFF, 0xFF00FF00,
 0xFFFFFF00, 0xFFFF0000
 Shader s = new SweepGradient(0, 0, mColors, null);
 mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
 mPaint.setShader(s);
 mPaint.setStyle(Paint.Style.STROKE);
 mPaint.setStrokeWidth(32);
 mCenterPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
 mCenterPaint.setColor(color);
 mCenterPaint.setStrokeWidth(5);
 private boolean mTrackingCenter;
 private boolean mHighlightCenter;
 @Override
 protected void onDraw(Canvas canvas) {
 float r = CENTER_X - mPaint.getStrokeWidth()*0.5f;
 canvas.translate(CENTER_X, CENTER_X);
 canvas.drawOval(new RectF(-r, -r, r, r), mPaint);
 canvas.drawCircle(0, 0, CENTER_RADIUS, mCenterPaint);
 if (mTrackingCenter) {
 int c = mCenterPaint.getColor();
 mCenterPaint.setStyle(Paint.Style.STROKE);
 if (mHighlightCenter) {
 mCenterPaint.setAlpha(0xFF);
 } else {
 mCenterPaint.setAlpha(0x80);
 canvas.drawCircle(0, 0,
 CENTER_RADIUS + mCenterPaint.getStrokeWidth(),
 mCenterPaint);
 mCenterPaint.setStyle(Paint.Style.FILL);
 mCenterPaint.setColor(c);
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 setMeasuredDimension(CENTER_X*2, CENTER_Y*2);
 private static final int CENTER_X = 100;
 private static final int CENTER_Y = 100;
 private static final int CENTER_RADIUS = 32;
 private int floatToByte(float x) {
 int n = java.lang.Math.round(x);
 return n;
 private int pinToByte(int n) {
 if (n < 0) {
 n = 0;
 } else if (n > 255) {
 n = 255;
 return n;
 private int ave(int s, int d, float p) {
 return s + java.lang.Math.round(p * (d - s));
 private int interpColor(int colors[], float unit) {
 if (unit <= 0) {
 return colors[0];
 if (unit >= 1) {
 return colors[colors.length - 1];
 float p = unit * (colors.length - 1);
 int i = (int)p;
 p -= i;
 // now p is just the fractional part [0...1) and i is the index
 int c0 = colors[i];
 int c1 = colors[i+1];
 int a = ave(Color.alpha(c0), Color.alpha(c1), p);
 int r = ave(Color.red(c0), Color.red(c1), p);
 int g = ave(Color.green(c0), Color.green(c1), p);
 int b = ave(Color.blue(c0), Color.blue(c1), p);
 return Color.argb(a, r, g, b);
 private int rotateColor(int color, float rad) {
 float deg = rad * 180 / 3.1415927f;
 int r = Color.red(color);
 int g = Color.green(color);
 int b = Color.blue(color);
 ColorMatrix cm = new ColorMatrix();
 ColorMatrix tmp = new ColorMatrix();
 cm.setRGB2YUV();
 tmp.setRotate(0, deg);
 cm.postConcat(tmp);
 tmp.setYUV2RGB();
 cm.postConcat(tmp);
 final float[] a = cm.getArray();
 int ir = floatToByte(a[0] * r + a[1] * g + a[2] * b);
 int ig = floatToByte(a[5] * r + a[6] * g + a[7] * b);
 int ib = floatToByte(a[10] * r + a[11] * g + a[12] * b);
 return Color.argb(Color.alpha(color), pinToByte(ir),
 pinToByte(ig), pinToByte(ib));
 private static final float PI = 3.1415926f;
 @Override
 public boolean onTouchEvent(MotionEvent event) {
 float x = event.getX() - CENTER_X;
 float y = event.getY() - CENTER_Y;
 boolean inCenter = java.lang.Math.sqrt(x*x + y*y) <= CENTER_RADIUS;
 switch (event.getAction()) {
 case MotionEvent.ACTION_DOWN:
 mTrackingCenter = inCenter;
 if (inCenter) {
 mHighlightCenter = true;
 invalidate();
 break;
 case MotionEvent.ACTION_MOVE:
 if (mTrackingCenter) {
 if (mHighlightCenter != inCenter) {
 mHighlightCenter = inCenter;
 invalidate();
 } else {
 float angle = (float)java.lang.Math.atan2(y, x);
 // need to turn angle [-PI ... PI] into unit [0...1]
 float unit = angle/(2*PI);
 if (unit < 0) {
 unit += 1;
 mCenterPaint.setColor(interpColor(mColors, unit));
 invalidate();
 break;
 case MotionEvent.ACTION_UP:
 if (mTrackingCenter) {
 if (inCenter) {
 mListener.colorChanged(mCenterPaint.getColor());
 mTrackingCenter = false; // so we draw w/o halo
 invalidate();
 break;
 return true;
 public ColorPickerDialog(Context context,
 OnColorChangedListener listener,
 int initialColor) {
 super(context);
 mListener = listener;
 mInitialColor = initialColor;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 OnColorChangedListener l = new OnColorChangedListener() {
 public void colorChanged(int color) {
 mListener.colorChanged(color);
 dismiss();
 };
 setContentView(new ColorPickerView(getContext(), l, mInitialColor));
 setTitle("Pick a Color");