在画布上绘图 - PorterDuff.Mode.CLEAR 绘制黑色！为什么?

问题描述

我正在尝试创建一个自定义视图，它的工作很简单:有一个由弧形路径显示的位图 - 从 0deg 到 360deg.度数随着某些 FPS 的变化而变化.

I'm trying to create a custom View which works simple: there is a Bitmap which is revealed by arc path - from 0deg to 360deg. Degrees are changing with some FPS.

所以我使用重写的 onDraw() 方法制作了一个自定义视图:

So I made a custom View with overridden onDraw() method:

@Override
protected void onDraw(Canvas canvas) {

    canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
    arcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));
    canvas.drawArc(arcRectF, -90, currentAngleSweep, true, arcPaint);
    arcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    canvas.drawBitmap(bitmap, circleSourceRect, circleDestRect, arcPaint);
}

arcPaint 初始化如下:

arcPaint = new Paint();
arcPaint.setAntiAlias(true);
arcPaint.setColor(Color.RED); // Color doesn't matter

现在，一切都画得很好，但是......整个视图的背景都是黑色的.

Now, everything draws great, but... the background is BLACK in whole View.

如果我设置 canvas.drawColor(..., PorterDuff.Mode.DST) 并省略 canvas.drawBitmap() - 在透明背景上正确绘制圆弧.

If I set canvas.drawColor(..., PorterDuff.Mode.DST) and omit canvas.drawBitmap() - the arc is drawn properly on transparent background.

我的问题是 - 如何设置 PorterDuff 模式以使其具有透明度?

My question is - how to set PorterDuff modes to make it work with transparency?

当然 bitmap 是带有 alpha 通道的 32 位 PNG.

Of course bitmap is 32-bit PNG with alpha channel.

推荐答案

PorterDuff.Mode.CLEAR 不适用于硬件加速.只需设置

PorterDuff.Mode.CLEAR doesn't work with hardware acceleration. Just set

view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);

非常适合我.

这篇关于在画布上绘图 - PorterDuff.Mode.CLEAR 绘制黑色！为什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！