我按照指纹代码和其他一些代码来创建一个应用程序，允许您绘制到屏幕上，背景图像就位于顶部。另外，我想制作一个擦除笔的橡皮擦工具，而不是背景图像。我想我必须使用两个画布，但无法弄清楚它如何与Canvas的onDraw一起使用。
这是我的代码。现在笔绘图工作，橡皮擦绘图擦除但它擦除背景图像。我只想要它擦掉笔。
如果你能给我一些关于该做什么的提示，我会非常感激。
===
//MainActivity.java
public class MainActivity extends Activity implements OnClickListener {
public MyView myView;
boolean penOn;
boolean eraserOn;
Bitmap bMap;
private Canvas mCanvas;
private Canvas myForegroundCanvas;
private Path mPath;
private Bitmap mBitmap;
private Paint mPaint, mBitmapPaint;
private ArrayList<DrawAction> paths = new ArrayList<DrawAction>();
private ArrayList<DrawAction> undonePaths = new ArrayList<DrawAction>();
int selectedColor=Color.RED;
RelativeLayout container;
private int width;
private int height;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
View mainView = getLayoutInflater().inflate(R.layout.activity_main,
null);
myView = new MyView(this);
container = (RelativeLayout) mainView.findViewById(R.id.container);
container.addView(myView);
setContentView(mainView);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.RED);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(16);
Button pen = (Button) mainView.findViewById(R.id.buttonpen);
pen.setOnClickListener(this);
Button eraser = (Button) mainView.findViewById(R.id.buttonerase);
eraser.setOnClickListener(this);
pen.bringToFront();
eraser.bringToFront();
}
public class MyView extends View {
public MyView(Context c) {
super(c);
if (android.os.Build.VERSION.SDK_INT >= 11) {
setLayerType(View.LAYER_TYPE_SOFTWARE, null);
}
DisplayMetrics displaymetrics = new DisplayMetrics();
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
Display display = getWindowManager().getDefaultDisplay();
Point size = new Point();
display.getSize(size);
MainActivity.this.width = size.x;
MainActivity.this.height = size.y;
bMap = getBitmapFromAsset(MainActivity.this, "google.png");
Bitmap background = Bitmap.createScaledBitmap(bMap,
MainActivity.this.width, MainActivity.this.height, false);
mBitmap = background.copy(Bitmap.Config.ARGB_8888, true);
mCanvas = new Canvas(mBitmap);
myForegroundCanvas = new Canvas(mBitmap);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(Color.TRANSPARENT);
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
Paint textPaint = new Paint();
textPaint.setTextSize(40);
final Iterator<DrawAction> i = paths.iterator();
while (i.hasNext()) {
final DrawAction d = i.next();
if (d.type.equals("pen")) {
mPaint.setColor(d.color);
mPaint.setXfermode(null);// clear the draw
canvas.drawPath(d.path, mPaint);
// myForegroundCanvas.drawPath(d.path, mPaint);
} else if (d.type.equals("eraser")) {
// mPaint.setAlpha(0xFF);//transperent color
mPaint.setXfermode(new PorterDuffXfermode(
PorterDuff.Mode.CLEAR));// clear the draw
canvas.drawPath(d.path, mPaint);
// myForegroundCanvas.drawPath(d.path, mPaint);
}
}
mPaint.setColor(selectedColor);
canvas.drawPath(mPath, mPaint);
// canvas.drawCanvas(myForegroundCanvas, 0, 0, null);
}
private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;
private void touch_start(float x, float y) {
undonePaths.clear();
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
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;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
DrawAction d = new DrawAction(mPath, Color.RED);
paths.add(d);
mPath = new Path();
}
private void touch_start_eraser(float x, float y) {
undonePaths.clear();
mPaint.setColor(Color.WHITE);
selectedColor=Color.WHITE;
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move_eraser(float x, float y) {
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;
}
}
private void touch_up_eraser() {
mPath.lineTo(mX, mY);
DrawAction d = new DrawAction(mPath, true);
paths.add(d);
mPath = new Path();
}
@Override
public boolean onTouchEvent(MotionEvent event) {
if ( !penOn && eraserOn) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
touch_start_eraser(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touch_move_eraser(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up_eraser();
invalidate();
break;
}
return true;
} else {
float x = event.getX();
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;
}
}
}
public Bitmap getBitmapFromAsset(Context context, String strName) {
AssetManager assetManager = context.getAssets();
InputStream istr;
Bitmap bitmap = null;
try {
istr = assetManager.open(strName);
bitmap = BitmapFactory.decodeStream(istr);
} catch (IOException e) {
return null;
}
return bitmap;
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.buttonpen:
penOn=true;
eraserOn=false;
break;
case R.id.buttonerase:
penOn=false;
eraserOn=true;
break;
}
}
}
===
//DrawAction.java, a helper class for holding the path and what type of drawing to do (pen or erase)
public class DrawAction {
public String type;
public Path path;
public int color;
public DrawAction(final Path p, final int color) {
this.type="pen";
this.path=p;
this.color=color;
}
public DrawAction(final Path p, final boolean isEraser) {
this.type="eraser";
this.path=p;
}
}
====
//activity_main.xml the layout code
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.doodle5.MainActivity"
tools:ignore="MergeRootFrame" >
<Button
android:id="@+id/buttonpen"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="25dp"
android:layout_marginRight="25dp"
android:layout_marginTop="50dp"
android:text="Pen" />
<Button
android:id="@+id/buttonerase"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_marginRight="25dp"
android:layout_marginTop="50dp"
android:text="Erase" />
</RelativeLayout>
答案 0 :(得分：1)
我明白了。我最终将背景图像作为背景绘制在容器上，而不是将其绘制到画布上。
在onDraw中我注释掉了这一行：
canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
在onCreate中我添加了：
BitmapDrawable ob = new BitmapDrawable(backgroundBitmap);
container.setBackgroundDrawable(ob);