在我的项目中,我有一个位图填充整个屏幕.在这个位图上,我绘制了一个路径

android.graphics.Canvas.drawPath(Path path, Paint paint)

设置绘画以便描边和填充路径的内容.我将实现的是擦除与路径相交的bitamp部分.我设法使用另一个bitmmap而不是路径,并使用porter duff规则获得相同的行为.有没有机会对路径做同样的事情？

    mPaintPath.setARGB(100, 100, 100, 100);// (100, 100, 100, 100)
    mPaintPath.setStyle(Paint.Style.FILL_AND_STROKE);
    mPaintPath.setAntiAlias(true);
    mPath.moveTo(x0, y0));
    mPath.lineTo(x1, y1);
    mPath.lineTo(x2, y2);
    mPath.lineTo(x3, y3);
    mPath.lineTo(x0, y0);
    mPath.close();
    c.drawPath(mPath, mPaintPath);

解决方法:

当然,只需将路径绘制到屏幕外缓冲区,以便在绘制位图时将其用作蒙版,如下所示：

// Create an offscreen buffer
int layer = c.saveLayer(0, 0, width, height, null,
        Canvas.HAS_ALPHA_LAYER_SAVE_FLAG | Canvas.FULL_COLOR_LAYER_SAVE_FLAG);

// Setup a paint object for the path
mPaintPath.setARGB(255, 255, 255, 255);
mPaintPath.setStyle(Paint.Style.FILL_AND_STROKE);
mPaintPath.setAntiAlias(true);

// Draw the path onto the offscreen buffer
mPath.moveTo(x0, y0);
mPath.lineTo(x1, y1);
mPath.lineTo(x2, y2);
mPath.lineTo(x3, y3);
mPath.lineTo(x0, y0);
mPath.close();
c.drawPath(mPath, mPaintPath);

// Draw a bitmap on the offscreen buffer and use the path that's already
// there as a mask
mBitmapPaint.setXfermode(new PorterDuffXfermode(Mode.SRC_OUT));
c.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

// Composit the offscreen buffer (a masked bitmap) to the canvas
c.restoreToCount(layer);

如果你能够抵抗锯齿,那么有一种更简单的方法：只需设置一个剪辑路径(注意使用Region.Op.DIFFERENCE会导致路径的内部被剪掉而不是剪切路径之外的所有内容)：

// Setup a clip path
mPath.moveTo(x0, y0);
mPath.lineTo(x1, y1);
mPath.lineTo(x2, y2);
mPath.lineTo(x3, y3);
mPath.lineTo(x0, y0);
mPath.close();
c.clipPath(mPath, Op.DIFFERENCE);

// Draw the bitmap using the path clip
c.drawBitmap(mBitmap, 0, 0, mBitmapPaint);