我有一个阿尔法掩码，我想把这个掩码用作橡胶，当用户触摸屏幕时，位图的那一部分应该被擦除为阿尔法掩码的形状。我试过了，但它总是把整个位图作为掩码，而不是alpha部分。稍后，用户将保存位图，以便删除的部分应该是透明的。
这是我使用的代码：
paintMask.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
Canvas canvas = new Canvas(bitmapOriginal);
int sc = canvas.saveLayer(0, 0, width, height, null, Canvas.ALL_SAVE_FLAG);
canvas.drawBitmap(bitmapOriginal, 0, 0, null);
canvas.drawBitmap(bitmapMask, 0, 0, paintMask);
canvas.restoreToCount(sc);
public class DrawingView extends View implements View.OnTouchListener {
private int x = 0;
private int y = 0;
Bitmap bitmap;
Path circlePath;
Paint circlePaint;
private final Paint paint = new Paint();
private final Paint eraserPaint = new Paint();
public DrawView(Context context){
super(context);
setFocusable(true);
setFocusableInTouchMode(true);
this.setOnTouchListener(this);
// Set background
this.setBackgroundColor(Color.CYAN);
bp = BitmapFactory.decodeResource(getResources(), R.drawable.bg);
// Set bitmap
bitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);
bitmapCanvas = new Canvas();
bitmapCanvas.setBitmap(bitmap);
bitmapCanvas.drawColor(Color.TRANSPARENT);
bitmapCanvas.drawBitmap(bp, 0, 0, null);
circlePath = new Path();
circlePaint = new Paint();
circlePaint.setAntiAlias(true);
circlePaint.setColor(Color.BLUE);
circlePaint.setStyle(Paint.Style.STROKE);
circlePaint.setStrokeJoin(Paint.Join.MITER);
circlePaint.setStrokeWidth(4f);
// Set eraser paint properties
eraserPaint.setAlpha(0);
eraserPaint.setStrokeJoin(Paint.Join.ROUND);
eraserPaint.setStrokeCap(Paint.Cap.ROUND);
eraserPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
eraserPaint.setAntiAlias(true);
}
@Override
public void onDraw(Canvas canvas) {
canvas.drawBitmap(bitmap, 0, 0, paint);
bitmapCanvas.drawCircle(x, y, 30, eraserPaint);
canvas.drawPath(circlePath, circlePaint);
}
public boolean onTouch(View view, MotionEvent event) {
x = (int) event.getX();
y = (int) event.getY();
bitmapCanvas.drawCircle(x, y, 30, eraserPaint);
circlePath.reset();
circlePath.addCircle(x, y, 30, Path.Direction.CW);
int ac=event.getAction();
switch(ac){
case MotionEvent.ACTION_UP:
Toast.makeText(MainActivity.this, String.valueOf(x), Toast.LENGTH_SHORT).show();
circlePath.reset();
break;
}
invalidate();
return true;
}
}
和布局文件中
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="#00ff00"
tools:context=".MainActivity">
<DrawingView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/ln1"
android:orientation="vertical"
/></LinearLayout>
希望它能帮助