8

我正在玩位图蒙版,在尝试使用Paint绘制ALPHA_8位图蒙版时偶尔会发现一个有趣的问题。PorterDuff.Mode.DST_IN它只是不起作用,至少在 Android 6.x 和 5.x 上是这样。
这是我的示例可绘制代码:

public class MaskedDrawablePorterDuffDstIn extends Drawable {

    private Bitmap mPictureBitmap;
    private Bitmap mMaskBitmap;
    private Bitmap mBufferBitmap;
    private Canvas mBufferCanvas;
    private final Paint mPaintDstIn = new Paint();

    public MaskedDrawablePorterDuffDstIn() {
        mPaintDstIn.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
    }

    @Override
    public void draw(Canvas canvas) {
        if (mPictureBitmap == null || mMaskBitmap == null) {
            return;
        }

        mBufferCanvas.drawBitmap(mPictureBitmap, 0, 0, null);
        mBufferCanvas.drawBitmap(mMaskBitmap, 0, 0, mPaintDstIn);
        canvas.drawBitmap(mBufferBitmap, 0, 0, null);
    }

    @Override
    protected void onBoundsChange(Rect bounds) {
        super.onBoundsChange(bounds);
        final int width = bounds.width();
        final int height = bounds.height();

        if (width <= 0 || height <= 0) {
            return;
        }

        mBufferBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        mBufferCanvas = new Canvas(mBufferBitmap);
    }
...

mMaskBitmapARGB_8888配置它工作得很好。但是当我使用ALPHA_8它时不会。在这种情况下,图片根本没有被掩盖。

这是我在 Activity 中加载资源的方式:

private void loadImages() {
    mPictureBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.picture);
    mMaskBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.mask_circle).extractAlpha();
}

请注意.extractAlpha()哪个给了我ALPHA_8位图。

以下是我使用 Drawable 的方法:

public void setDrawablePDDstIn(View view) {
    MaskedDrawablePorterDuffDstIn maskedDrawable = new MaskedDrawablePorterDuffDstIn();
    maskedDrawable.setPictureBitmap(mPictureBitmap);
    maskedDrawable.setMaskBitmap(mMaskBitmap);
    mImageView.setImageDrawable(maskedDrawable);
}

更有趣的是,当我尝试另一种方法时,先绘制蒙版,然后使用SRC_INPaint 绘制图片 - 它再次正常工作,即使使用ALPHA_8蒙版:

public class MaskedDrawablePorterDuffSrcIn extends Drawable {

    private Bitmap mPictureBitmap;
    private Bitmap mMaskBitmap;
    private Bitmap mBufferBitmap;
    private Canvas mBufferCanvas;
    private final Paint mPaintSrcIn = new Paint();

    public MaskedDrawablePorterDuffSrcIn() {
        mPaintSrcIn.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    }
    @Override
    public void draw(Canvas canvas) {
        if (mPictureBitmap == null || mMaskBitmap == null) {
            return;
        }

        mBufferCanvas.drawBitmap(mMaskBitmap, 0, 0, null);
        mBufferCanvas.drawBitmap(mPictureBitmap, 0, 0, mPaintSrcIn);

        //dump the buffer
        canvas.drawBitmap(mBufferBitmap, 0, 0, null);
    }

...

这是我在GitHub 上试验的整个项目的链接。它包含非工作和工作解决方案,请随意使用。

任何人都知道为什么组合DST_INALPHA_8不按预期工作?

4

0 回答 0