使用路径绘制圆形扇区

Question

我想画这样的东西：

因此，我想在每张照片上放置一个带有黑色区域的圆形扇形（切割弧）。我如何使用例如来实现这一点

canvas.draw(Path path, Paint paint);

我在下面尝试过，但没有达到我想要的效果：

Path path = new Path();
path.setFillType(Path.FillType.EVEN_ODD);
path.addCircle(getWidth() / 2, getHeight() / 2, getHeight() / 2, Path.Direction.CW);
path.addRect(0, getHeight() - 70, getWidth(), getHeight(), Path.Direction.CW);

Answer 1

你几乎让它工作了。您只需要在绘制之前剪切画布并使用Path.FillType.INVERSE_EVEN_ODD 来绘制您的扇区：

// Limit the drawable region of the canvas (saving the state before)
canvas.save();
canvas.clipRect(new Rect(0, canvas.getHeight() - 70, canvas.getWidth(), canvas.getHeight()));

Path path = new Path();
path.setFillType(Path.FillType.INVERSE_EVEN_ODD);
path.addCircle(canvas.getWidth() / 2, canvas.getHeight() / 2, canvas.getHeight() / 2, Path.Direction.CW);
path.addRect(0, canvas.getHeight() - 70, canvas.getWidth(), canvas.getHeight(), Path.Direction.CW);
canvas.drawPath(path, paint);

// Restore the canvas to the saved state to remove clip
canvas.restore();

// Draw more things on the canvas...

或者，您可以使用Canvas.drawArc (documentation)

我假设您的问题是您需要为您的扇区分配一个固定高度，因此您需要根据该高度计算 startAngle 和 sweepAngle（drawArc 方法的参数）（假设一个正方形图片）。这是示例代码（API 级别 15 兼容）：

int sectorHeigh = 70; // The height of your sector in pixels

// Compute the start angle based on your desired sector height
float startAngle = (float) Math.toDegrees(Math.asin((canvas.getHeight() / 2f - sectorHeigh) / (canvas.getHeight() / 2f)));
// Add the arc (calculating the sweepAngle based on startAngle)
canvas.drawArc(new RectF(0, 0, canvas.getWidth(), canvas.getHeight()), startAngle, 2 * (90 - startAngle), false, paint);

另一种使用弧线绘制扇区的方法是创建Path 对象，使用Path.addArc (documentation) 添加弧线，然后使用Canvas.drawPath (documentation) 绘制它。