Canvas.clipPath（路径）不削波如预期 [英] Canvas.clipPath(Path) not clipping as expected

问题描述

我想剪辑画布绘制操作弧形的楔形。不过，我没有收到剪切路径设置到画布后的预期结果。

有关说明，这里是我在做什么：

  path.reset（）;

//移动到点＃1
path.moveTo（rect.centerX（），rect.centerY（））;

//每页文档，这将绘制的连接线从目前的
//位置到弧（在0度）的开始位置，添加弧
//我现在的位置现在位于在＃2。
path.arcTo（矩形，0，-30）;

//这应该然后关闭路径，精加工回在中心点（＃3）
path.close（）;
 

这工作，当我简单地画这条道路（ canvas.drawPath（路径，涂料））它绘制楔形，如上图所示。然而，当我把这个路径作为画布的剪辑路径，并绘制成的：

  //我已经尝试过了有和没有Region.Op参数
canvas.clipPath（路径，Region.Op.REPLACE）;
canvas.drawColor（Color.BLUE）;
 

我得到以下的结果，而不是（楔形留给只是为了显示参考）：

所以，反而好像夹到路径的边界RECT，而不是路径本身。任何想法这里发生了什么？

修改只是作为一个更新，我发现一个更有效的方式这样做，允许硬件加速。首先，绘制整个图像（你会被裁剪）到屏幕外的位图。做一个 BitmapShader 使用该位图，设置着色器到油漆，然后利用得出的楔形路径油漆目标：

  drawMyBitmap（位）;
着色的着色器=新BitmapShader（位图，Shader.TileMode.CLAMP，Shader.TileMode.CLAMP）;
涂料粉刷=新的油漆（Paint.ANTI_ALIAS_FLAG）;
paint.setShader（着色）;

@覆盖
公共无效的OnDraw（帆布油画）{
    canvas.drawArc（矩形，//该矩形边界圆
                   startAngle开始，//角度（CW从3点）开始
                   sweepAngle，//弧的角度（​​CW从3点钟方向）
                   如此，是否绘制填充圆弧//布尔（楔）
                   //油漆涂料附着着色器
    ）;
}
 

解决方案

您使用HC或以上或以其它方式使用硬件加速？

如果是这样，clipPath是不支持的和有问题的。

<一个href="http://developer.android.com/guide/topics/graphics/hardware-accel.html">developer.android.com/guide/topics/graphics/hardware-accel.html.

I'm trying to clip a canvas drawing operation to an arc-shaped wedge. However, I'm not getting the intended result after setting the clipping path to the canvas.

For illustration, here is what I'm doing:

path.reset();

//Move to point #1
path.moveTo(rect.centerX(), rect.centerY());

//Per the documentation, this will draw a connecting line from the current
//position to the starting position of the arc (at 0 degrees), add the arc
//and my current position now lies at #2.
path.arcTo(rect, 0, -30);

//This should then close the path, finishing back at the center point (#3)
path.close();

This works, and when I simply draw this path (canvas.drawPath(path, paint)) it draws the wedge as shown above. However, when I set this path as the canvas's clipping path and draw into it:

//I've tried it with and without the Region.Op parameter
canvas.clipPath(path, Region.Op.REPLACE);
canvas.drawColor(Color.BLUE);

I get the following result instead (the wedge is left just to show reference):

So it instead seems to clip to the bounding rect of the Path, and not the Path itself. Any ideas what's happening here?

EDIT Just as an update, I've found a much more efficient way of doing this that allows for hardware acceleration. First, draw the entire image (that you'd be clipping) into an offscreen bitmap. Make a BitmapShader using this Bitmap, set that shader to a Paint, then draw the wedge path using that Paint object:

drawMyBitmap(bitmap);
Shader shader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setShader(shader);

@Override
public void onDraw(Canvas canvas) {
    canvas.drawArc(rect,         //The rectangle bounding the circle
                   startAngle,   //The angle (CW from 3 o'clock) to start
                   sweepAngle,   //The angle (CW from 3 o'clock) of the arc
                   true,         //Boolean of whether to draw a filled arc (wedge)
                   paint         //The paint with the shader attached
    );
}

解决方案

Are you using HC or above or otherwise using hardware acceleration?

If so, clipPath is unsupported and problematic.

developer.android.com/guide/topics/graphics/hardware-accel.html.

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