如何在屏幕中央创建一个透明的曲线矩形？

Question

如何在屏幕中央创建一个透明的曲线矩形？

我已经编写了以下代码，并为屏幕中央的曲线矩形添加了alpha值，但是背景颜色显示出来而不是透明。

int width = canvas.getWidth();
int height = canvas.getHeight();
Rect childRect = this.getChildRect();

Paint outerPaint = new Paint();
outerPaint.setColor(Color.LTGRAY);
borderPaint.setStyle(Paint.Style.FILL);


Paint innerPaint = new Paint();
innerPaint.setARGB(0, 0, 0, 0);
innerPaint.setAlpha(0);
innerPaint.setStyle(Paint.Style.FILL);

canvas.drawRect(0.0F, 0.0F, width, height, outerPaint);
canvas.drawRoundRect(new RectF(childRect.left, childRect.top, childRect.right, childRect.bottom), 8F, 8F, innerPaint);

- Aj08

Answer 1

你可以使用 setXfermode() 方法，通过将参数设置为 PorterDuff.Mode.ADD 以及 PorterDuff.Mode.ADD，来获取内部透明区域而不是将 alpha 值添加到画笔中。

请在代码中进行以下更改：

int width = canvas.getWidth();
int height = canvas.getHeight();
Rect childRect = this.getChildRect();

Paint outerPaint = new Paint();
outerPaint.setColor(Color.LTGRAY);
outerPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.ADD));
outerPaint.setAntiAlias(true);

Paint innerPaint = new Paint();
innerPaint.setColor(Color.TRANSPARENT);
innerPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
innerPaint.setAntiAlias(true);

canvas.drawRect(0.0F, 0.0F, width, height, outerPaint);
canvas.drawRoundRect(new RectF(childRect.left, childRect.top, childRect.right, childRect.bottom), 8F, 8F, innerPaint);

- Arshak