android - 通过在android中拖动一个圆圈来制作下面的图像

Question

在我的实现中，我有两张图片，一张叠加在另一张上。因为，我将一个圆形对象移动到顶部图像上，我想让圆形内部的那个区域透明，这样我就可以看到下面的图像。例如，我有两个图像 - 汽车图像及其框架图像。我将汽车图像覆盖在框架图像上，当我在汽车图像上拖动一个圆圈时，它应该显示下面的框架。

我试图搜索很多但没有得到任何指示。在某处我读到我需要使用 alpha 遮罩或使用 porterduff 和 xfermode 的图像遮罩。但我不明白。

具体来说，

我怎样才能使上面的图像透明，我怎样才能只使圆圈内的区域透明？

谢谢你

score 0 · Accepted Answer

我使用了来自问题PorterduffXfermode: Clear a section of a bitmap 的有用输入。在下面的示例中，触摸区域变为“透明”，并且可以观察down_image下方的部分up_image（两个图像都只是资源中的 jpg 可绘制对象）。

基本上有两种可能的实现：

禁用绘图的硬件加速，这将使PorterDuff.Mode.CLEAR视图透明（有关硬件加速效果的更多详细信息，请参阅此处）：

活动：

public class MyActivity extends Activity {
    /** Overlay image */
    private DrawingView mDrawingView = null;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        requestWindowFeature(Window.FEATURE_NO_TITLE);

        final RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
            ViewGroup.LayoutParams.MATCH_PARENT);

        // Create the view for the xfermode test
        mDrawingView = new DrawingView(this);

        params.addRule(RelativeLayout.CENTER_IN_PARENT);
        mDrawingView.setLayoutParams(params);

        final RelativeLayout relativeLayout = new RelativeLayout(this);

        relativeLayout.setBackgroundResource(R.drawable.down_image);
        relativeLayout.addView(mDrawingView);

        // Main part of the implementation - make layer drawing software
        if (android.os.Build.VERSION.SDK_INT >= 11) {
            mDrawingView.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        }

        // Show the layout with the test view
        setContentView(relativeLayout);
    }
}

绘图视图：

/**
 * View which makes touch area transparent
 */
public class DrawingView extends View {
    /**  Paint to clear touch area */
    private Paint mClearPaint = null;
    /** Main bitmap */
    private Bitmap mBitmap = null;

    /** X coordinate of touch circle */
    private int mXTouch = -1;
    /** Y coordinate of touch circle */
    private int mYTouch = -1;
    /** Radius of touch circle */
    private int mRadius = 0;

    /**
     * Default constructor
     *
     * @param ct {@link Context}
     */
    public DrawingView(final Context ct) {
        super(ct);

        // Generate bitmap used for background
        mBitmap = BitmapFactory.decodeResource(ct.getResources(), R.drawable.up_image);

        // Generate array of paints
        mClearPaint = new Paint();
        mClearPaint.setARGB(255, 255, 255, 0);
        mClearPaint.setStrokeWidth(20);
        mClearPaint.setStyle(Paint.Style.FILL);

        // Set all transfer modes
        mClearPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

        mRadius = getResources().getDimensionPixelSize(R.dimen.radius);
    }

    @Override
    public void onDraw(final Canvas canv) {
        // Background colour for canvas
        canv.drawColor(Color.argb(255, 0, 0, 0));

        // Draw the bitmap leaving small outside border to see background
        canv.drawBitmap(mBitmap, null, new RectF(0, 0, getMeasuredWidth(), getMeasuredHeight()), null);

        // Loop, draws 4 circles per row, in 4 rows on top of bitmap
        // Drawn in the order of mClearPaint (alphabetical)
        if (mXTouch > 0 && mYTouch > 0) {
            canv.drawCircle(mXTouch, mYTouch, mRadius, mClearPaint);
        }
    }

    @Override
    public boolean onTouchEvent(final MotionEvent event) {
        boolean handled = false;

        // get touch event coordinates and make transparent circle from it
        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
            case MotionEvent.ACTION_MOVE:
                mXTouch = (int) event.getX();
                mYTouch = (int) event.getY();
                // TODO: Note, in case of large scene it's better not to use invalidate without rectangle specified
                invalidate();
                handled = true;
                break;

            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_POINTER_UP:
            case MotionEvent.ACTION_CANCEL:
                mXTouch = -1;
                mYTouch = -1;
                // TODO: Note, in case of large scene it's better not to use invalidate without rectangle specified
                invalidate();
                handled = true;
                break;

            default:
                // do nothing
                break;
        }

        return super.onTouchEvent(event) || handled;
    }
}

采用这个解决方案，但看起来它取决于 Android 版本，因为建议的解决方案根本不适用于我的 4.2 设备。

android - 通过在android中拖动一个圆圈来制作下面的图像

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