在安卓系统上为imageView渲染圆角

Question

我有下面这段代码来渲染一个圆角的imageView。

public class RoundedCornerImageView extends ImageView {

private int rounded;
public RoundedCornerImageView(Context context) {
    super(context);
}

public RoundedCornerImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public RoundedCornerImageView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}


public int getRounded() {
    return rounded;
}

public void setRounded(int rounded) {
    this.rounded = rounded;

}


@Override
public void onDraw(Canvas canvas)
{


    Drawable drawable = getDrawable();

    int w = drawable.getIntrinsicHeight(),
        h = drawable.getIntrinsicWidth();

    Bitmap rounder = Bitmap.createBitmap(w,h,Bitmap.Config.ARGB_8888);
    Canvas tmpCanvas = new Canvas(rounder);

    // We're going to apply this paint eventually using a porter-duff xfer mode.
    // This will allow us to only overwrite certain pixels. RED is arbitrary. This
    // could be any color that was fully opaque (alpha = 255)
    Paint xferPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    xferPaint.setColor(Color.WHITE);

    // We're just reusing xferPaint to paint a normal looking rounded box, the 20.f
    // is the amount we're rounding by.
    tmpCanvas.drawRoundRect(new RectF(0,0,w,h), 10.0f, 10.0f, xferPaint);

    // Now we apply the 'magic sauce' to the paint
    xferPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

    drawable.draw(canvas);
    canvas.drawBitmap(rounder, 0, 0, xferPaint);
}
}



<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:orientation="vertical"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:background='#a3deef'
    >
<com.example.scheduling_android.view.RoundedCornerImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/eventImageView"
        android:adjustViewBounds="false"/>
</LinearLayout>

它的工作原理是，它确实将图像的角落裁剪掉了。然而，当我试图在一个背景颜色为#a3deef的linearLayout中呈现它时，问题就出现了。结果显示的背景颜色为#a3deef，每个图像都以圆角显示，其中4个裁剪的角全部为黑色。

我应该怎么做，使裁剪的角落透明，而不是黑色？另外，如果有人能向我解释为什么它会是黑色的，而不是其他颜色的，那就太好了！

提前谢谢。

Answer 1

如果源还不是Bitmap，那么所采用的方法就不能很好地工作，主要是因为最好使用绘图回调之外的传输模式将内容绘制到Canvas中(因此它只发生一次，而不是在每次绘制刷新时)，并且调用Drawable.draw() anywhere不会产生正确的结果，因为界限不会像您预期的那样设置。

执行此操作的一种明显更有效的方法是不修改源数据，而只是将四舍五入的剪裁应用于绘图Canvas。对于非常大的半径，这可以创建一些锯齿，但在10px时它不会明显。这种方法唯一的另一个缺点是，硬件加速目前不支持clipPath()，因此您必须将此视图的图层类型设置为软件，以便在Android 3.0+上进行渲染。

public class RoundedCornerImageView extends ImageView {

    private Path roundedPath;
    private int rounded;

    public RoundedCornerImageView(Context context) {
        super(context);
        init();
    }

    public RoundedCornerImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public RoundedCornerImageView(Context context, AttributeSet attrs,
            int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    private void init() {
        // If the application is hardware accelerated,
        // must disable it for this view.
        setLayerType(View.LAYER_TYPE_SOFTWARE, null);
        // Set a default radius
        setRounded(10);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        if (w != oldw || h != oldh) {
            roundedPath = new Path();
            roundedPath.addRoundRect(new RectF(0, 0, w, h),
                    rounded, rounded, Path.Direction.CW);
        }
    }

    public int getRounded() {
        return rounded;
    }

    public void setRounded(int rounded) {
        this.rounded = rounded;
        roundedPath = new Path();
        roundedPath.addRoundRect(new RectF(0, 0, getWidth(), getHeight()),
                rounded, rounded, Path.Direction.CW);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        //Apply the clip
        canvas.clipPath(roundedPath);
        //Let the view draw as normal
        super.onDraw(canvas);
    }
}

在修改后的版本中，您只需在每次视图或半径大小更改时更新剪裁路径，并在绘制之前将该Path作为剪裁应用于Canvas。

HTH

Answer 2

添加以下行以使画布透明：

canvas.saveLayerAlpha(0, 0, canvas.getWidth(), canvas.getHeight(), 255, Canvas.HAS_ALPHA_LAYER_SAVE_FLAG);

此外，我使用反向填充的圆角矩形路径来遮罩位图，因此我不需要像您一样的中间遮罩位图。

public class RoundedImageView extends ImageView {

    private Path mMaskPath;
    private Paint mMaskPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private int mCornerRadius = 10;

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

        init();
    }

    public RoundedImageView(Context context, AttributeSet attributeSet) {
        super(context, attributeSet);

        init();
    }

    public RoundedImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        init();
    }

    private void init() {
        ViewCompat.setLayerType(this, ViewCompat.LAYER_TYPE_SOFTWARE, null);
        mMaskPaint.setXfermode(new PorterDuffXfermode(Mode.CLEAR));
    }

    /**
     * Set the corner radius to use for the RoundedRectangle.
     * 
     * @param Primitive int - The corner radius of the rounded rectangle.
     */
    public void setCornerRadius(int cornerRadius) {
        mCornerRadius = cornerRadius;
        generateMaskPath(getWidth(), getHeight());
        invalidate();
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldW, int oldH) {
        super.onSizeChanged(w, h, oldW, oldH);

        if (w != oldW || h != oldH) {
            generateMaskPath(w, h);
        }
    }

    private void generateMaskPath(int w, int h) {
        mMaskPath = new Path();
        mMaskPath.addRoundRect(new RectF(0,0,w,h), mCornerRadius, mCornerRadius, Direction.CW);
        mMaskPath.setFillType(FillType.INVERSE_WINDING);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if(canvas.isOpaque()) { // If canvas is opaque, make it transparent
            canvas.saveLayerAlpha(0, 0, canvas.getWidth(), canvas.getHeight(), 255, Canvas.HAS_ALPHA_LAYER_SAVE_FLAG);
        }

        super.onDraw(canvas);

        if(mMaskPath != null) {
            canvas.drawPath(mMaskPath, mMaskPaint);
        }
    }
}

Answer 3

这是因为您正在使用的Canvas是不透明的。非透明Canvas的背景为黑色。

This answer将SurfaceView的Canvas设置为透明。对你来说，这可能和将Bitmap的背景设置为透明一样简单。

Bitmap rounder = Bitmap.createBitmap(w,h,Bitmap.Config.ARGB_8888);
rounder.eraseColor(Color.TRANSPARENT);

你也可以在你的ImageView中尝试一下，将它的背景设置为100%透明：

setBackgroundColor(0);