Question

我需要在画布上绘制一个Bitmap，但我需要将黑色像素删除为透明。在Android中有一种简单的方法吗？ Bitmap.clearColor似乎行为不同。

Answer 1

检查以确保您创建的叠加位图实际上是透明的。使用配置ARGB_8888明确创建它。 http://developer.android.com/reference/android/graphics/Bitmap.Config.html

您可能希望将位图的创建移出reDraw方法，而只是创建一次。

Answer 2

它将在触摸上工作

  import android.app.Activity;
  import android.content.Context;
  import android.graphics.Bitmap;
  import android.graphics.Bitmap.Config;
  import android.graphics.BlurMaskFilter.Blur;
  import android.graphics.BitmapFactory;
  import android.graphics.BlurMaskFilter;
  import android.graphics.Canvas;
  import android.graphics.Color;
  import android.graphics.Paint;
  import android.graphics.PorterDuff.Mode;
  import android.graphics.PorterDuffXfermode;
  import android.os.Bundle;
  import android.view.MotionEvent;
  import android.view.View;

  public class StartActivity extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(new TouchView(this));


}

class TouchView extends View{
    Bitmap bgr;
    Bitmap overlayDefault;
    Bitmap overlay;
    Paint pTouch;
    int X = -100;
    int Y = -100;
    Canvas c2;

    public TouchView(Context context) {
        super(context);

        bgr = BitmapFactory.decodeResource(getResources(),R.drawable.bgr);
        overlayDefault = BitmapFactory.decodeResource(getResources(),R.drawable.over);
        overlay = BitmapFactory.decodeResource(getResources(),R.drawable.over).copy(Config.ARGB_8888, true);  
        c2 = new Canvas(overlay);

        pTouch = new Paint(Paint.ANTI_ALIAS_FLAG);         
        pTouch.setXfermode(new PorterDuffXfermode(Mode.SRC_OUT)); 
        pTouch.setColor(Color.TRANSPARENT);
        pTouch.setMaskFilter(new BlurMaskFilter(15, Blur.NORMAL));


    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {

        switch (ev.getAction()) {

            case MotionEvent.ACTION_DOWN: {

                X = (int) ev.getX();
                Y = (int) ev.getY();
                invalidate();

                break;
            }

            case MotionEvent.ACTION_MOVE: {

                    X = (int) ev.getX();
                    Y = (int) ev.getY();
                    invalidate();
                    break;

            }           

            case MotionEvent.ACTION_UP:

                break;

        }
        return true;
    }


    @Override
    public void onDraw(Canvas canvas){
        super.onDraw(canvas);

        //draw background
        canvas.drawBitmap(bgr, 0, 0, null);
        //copy the default overlay into temporary overlay and punch a hole in it                          
        c2.drawBitmap(overlayDefault, 0, 0, null); //exclude this line to show all as you draw
        c2.drawCircle(X, Y, 80, pTouch);
        //draw the overlay over the background  
        canvas.drawBitmap(overlay, 0, 0, null);

    }


}

}`

Answer 3

检查answer。它不被接受，但应该工作。不要忘记为使用此位图的视图启用硬件加速。

在画布上绘制位图，将黑色像素替换为透明

3 个答案: