在Android上隐藏一个可绘制/位图

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我目前正在寻找一种方法来使用黑白位图来屏蔽另一个位图的alpha通道,或者在Android上绘制。我很想知道做这件事的最佳方法是什么。我当然有几个关于如何做这件事的想法,但它们并不是最理想的。

我需要能够应用一个新的面具,每隔一次的图像。

任何关于如何实现这一目标的反馈都将不胜感激。

提问于
用户回答回答于

我得到它的工作,所以这是这样的:

    // we first same the layer, rectF is the area of interest we plan on drawing
    // this will create an offscreen bitmap
    canvas.saveLayer(rectF, null, Canvas.MATRIX_SAVE_FLAG
            | Canvas.CLIP_SAVE_FLAG | Canvas.HAS_ALPHA_LAYER_SAVE_FLAG
            | Canvas.FULL_COLOR_LAYER_SAVE_FLAG
            | Canvas.CLIP_TO_LAYER_SAVE_FLAG);

    // draw our unmasked stuff
    super.draw(canvas);
    // We same a layer again but this time we pass a paint object to mask
    // the above layer
    maskPaint = new Paint()
    maskPaint.setColor(0xFFFFFFFF);
    maskPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY));

    canvas.saveLayer(rectF, maskPaint,
            Canvas.MATRIX_SAVE_FLAG | Canvas.CLIP_SAVE_FLAG
                    | Canvas.HAS_ALPHA_LAYER_SAVE_FLAG
                    | Canvas.FULL_COLOR_LAYER_SAVE_FLAG
                    | Canvas.CLIP_TO_LAYER_SAVE_FLAG);
    // we draw the mask which is black and white. In my case
    // I have a path, and I use a blurPaint which blurs the mask slightly
    // You can do anti aliasing or whatever you which. Just black & white
    canvas.drawPath(path, blurPaint);
    // We restore twice, this merges the results upward
    // as each saveLayer() allocates a new drawing bitmap
    canvas.restore();
    canvas.restore();
用户回答回答于

我将这些变量声明为字段:

private Paint maskingPaint = new Paint();
private Drawable mask = <insert your drawable here>

然后,在onDraw()之外的某处,设置对象:

// Xfermode won't work if hardware accelerated
setLayerType(View.LAYER_TYPE_SOFTWARE, null);

// Using destination shape as a mask
// For a good explanation of PorterDuff transfer modes : http://ssp.impulsetrain.com/porterduff.html
maskingPaint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
maskingPaint.setAntiAlias(true);

// Position the mask
mask.setBounds(<insert your mask bounds here>);

最后,onDraw()方法应用掩码:

@Override
protected synchronized void onDraw(Canvas canvas)
{
    // Draw the mask first, making it the PorterDuff destination
    mask.draw(canvas);

    // Save the layer with the masking paint, that will be applied on restore()
    // Using CLIP_TO_LAYER_SAVE_FLAG to avoid any overflow of the masked image outside the mask bounds.
    Rect bounds = mask.getBounds();
    canvas.saveLayer(bounds.left, bounds.top, bounds.right, bounds.bottom, maskingPaint, 
            Canvas.CLIP_TO_LAYER_SAVE_FLAG);

    // Draw the shape offscreen, making it the PorterDuff source
    super.onDraw(canvas);

    // Apply the source to the destination, using SRC_IN transfer mode
    canvas.restore();
}

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