Question

我在画布上有两个点，现在我可以使用

在这些点之间绘制一条线，如下图所示

此代码canvas.drawLine(p1.x, p1.y, p2.x, p2.y, paint); enter image description here

我想在两个点之间绘制弧线，如下图所示。

enter image description here

我怎么画这样。

Answer 1

最后我从这段代码中得到了解决方案：

float radius = 20;
final RectF oval = new RectF();
oval.set(point1.x - radius, point1.y - radius, point1.x + radius, point1.y+ radius);
Path myPath = new Path();
myPath.arcTo(oval, startAngle, -(float) sweepAngle, true);

要计算startAngle，请使用以下代码：

int startAngle = (int) (180 / Math.PI * Math.atan2(point.y - point1.y, point.x - point1.x));

此处，point1表示您要开始绘制Arc的位置。 sweepAngle表示两条线之间的角度。我们必须通过使用两个点来计算它，比如我的问题图像中的蓝点。

Answer 2

做这样的事情：

@Override
protected void onDraw(Canvas canvas) {      
    Paint p = new Paint();
    RectF rectF = new RectF(50, 20, 100, 80);
    p.setColor(Color.BLACK);
    canvas.drawArc (rectF, 90, 45, true, p);
}

Answer 3

我试图做一些与众不同的事情，而且都是关于计算扫描和开始角度的。

我希望显示一个圆弧，表示从上到下的圆圈上的进度。

所以我从0到100有进度值，我希望显示一个从上到下开始的弧，以便在进度为100时填充圆圈。

要计算我使用的sweepAngle：

    int sweepAngle = (int) (360 * (getProgress() / 100.f));

接下来是计算startAngle

    int startAngle = 270 - sweepAngle / 2;

以这种方式计算起始角度，因为：

它始终从左侧开始，从上到下。所以顶部的起始角度等于270（注意它顺时针方向，0 = 3 o＆＃39;时钟，所以12 o＆＃39;时钟等于270度）
接下来我想计算我离开起点（270）的距离，并且我只计算扫描角度的一半，因为只有一半的弧线在左侧另一半在右边。

所以考虑到我有25％的进步

sweepAngle = 90 degrees (90 degrees is quarter of a circle)
start angle = 225 (45 degrees away from 270)

如果您希望从其他方面（从左到右，从右到左等）进度，您只需要在开始角度时替换270.

Answer 4

绘制弧的样本。

from jsonpath_ng.ext import parse

abilityname = "device_info"
propertyname = "manufacturer"
result = parse('$[?(@.name=="' + abilityname + '")].properties[?(@.name=="' + propertyname + '")]').find(myJson)
if len(result) == 1:
    return str(result[0].value['value'])
else:
    return ""

Answer 5

Langkiller提出了here一个简单的解决方案。从起点到控制点到终点画一条三次线。

Path path = new Path();
float startX = 0;
float startY = 2;
float controlX = 2;
float controlY = 4;
float endX = 4
float endY = 2
conePath.cubicTo(startX, startY, controlX, controlY,endX, endY);

Paint paint = new Paint();
paint.setARGB(200, 62, 90, 177);
paint.setStyle(Paint.Style.FILL);

canvas.drawPath(path, paint)

Answer 6

我可能来晚了，但我得到了更多信息。

Android Lollipop 之后，有两种方法可以解决此问题

public void drawArc（RectF椭圆形，float startAngle，float sweepAngle，   布尔useCenter，油漆）

public void drawArc（向左浮动，向顶部浮动，向右浮动，向下方浮动，   float startAngle，float sweepAngle，boolean useCenter，Paint paint）

用法：

   RectF rectF = new RectF(left, top, right, bottom);

    // method 1
    canvas.drawArc (rectF, 90, 45, true,  paints[0]);

    // method 2
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        canvas.drawArc (left, top, right, bottom, 0, 45, true, paints[1]);
    }

后掠角仅是顺时针绘制的扇形角。对于以下代码

private void drawArcs(Canvas canvas) {
    RectF rectF = new RectF(left, top, right, bottom);

    // white arc
    canvas.drawArc (rectF, 90, 45, true,  paints[0]);

    // Green arc
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        canvas.drawArc (left, top, right, bottom, 0, 45, true, paints[1]);
    }

    // Red stroked arc
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        canvas.drawArc (left, top, right, bottom, 180, 45, true,  paints[2]);
    }
}

结果将如下所示

可以通过定义路径，然后在onDraw方法中对其进行迭代来实现相同功能，如以下代码段所示：

 public class ArcDrawable extends Drawable {

    private int left, right, top, bottom;
    private  Paint[] paints = new Paint[3];
    private HashMap<Path, Paint> pathMap = new HashMap();


    public ArcDrawable() {

        // white paint
        Paint whitePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        whitePaint.setColor(Color.WHITE);
        paints[0]= whitePaint;

        // green paint
        Paint greenPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        greenPaint.setColor(Color.GREEN);
        paints[1]= greenPaint;

        // red paint
        Paint redPaint =new Paint(Paint.ANTI_ALIAS_FLAG);
        redPaint.setColor(Color.RED);
        redPaint.setStyle(Paint.Style.STROKE);
        paints[2]= redPaint;
    }

    @Override
    public void draw(Canvas canvas) {

        //----------USE PATHS----------
        // Define and use custom  Path
        for (Map.Entry<Path, Paint> entry : pathMap.entrySet()) {
            // Draw Path on respective Paint style
            canvas.drawPath(entry.getKey(),  entry.getValue());

        }

        // -------OR use conventional Style---------
        //drawArcs(canvas);

    }


    //Same result
    private void drawArcs(Canvas canvas) {
        RectF rectF = new RectF(left, top, right, bottom);

        // method 1
        canvas.drawArc (rectF, 90, 45, true,  paints[0]);

        // method 2
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            canvas.drawArc (left, top, right, bottom, 0, 45, true, paints[1]);
        }

        // method two with stroke
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            canvas.drawArc (left, top, right, bottom, 180, 45, true,  paints[2]);
        }
    }


    @Override
    protected void onBoundsChange(Rect bounds) {
        super.onBoundsChange(bounds);

        int width = bounds.width();
        int height = bounds.height();

        left = bounds.left;
        right = bounds.right;
        top = bounds.top;
        bottom = bounds.bottom;

        final int size = Math.min(width, height);
        final int centerX = bounds.left + (width / 2);
        final int centerY = bounds.top + (height / 2);

        pathMap.clear();
        //update pathmap using new bounds
        recreatePathMap(size, centerX, centerY);
        invalidateSelf();
    }


    private Path recreatePathMap(int size, int centerX, int centerY) {

        RectF rectF = new RectF(left, top, right, bottom);

        // first arc
        Path arcPath = new Path();
        arcPath.moveTo(centerX,centerY);
        arcPath.arcTo (rectF, 90, 45);
        arcPath.close();
        // add to draw Map
        pathMap.put(arcPath, paints[0]);

        //second arc
        arcPath = new Path();
        arcPath.moveTo(centerX,centerY);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
          arcPath.arcTo (rectF, 0, 45);
        }
        arcPath.close();
        // add to draw Map
        pathMap.put(arcPath, paints[1]);

        // third arc
        arcPath = new Path();
        arcPath.moveTo(centerX,centerY);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
            arcPath.arcTo (rectF, 180, 45);

        }
        arcPath.close();
        // add to draw Map
        pathMap.put(arcPath, paints[2]);

        return arcPath;

    }

    @Override
    public void setAlpha(int alpha) {

    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {

    }

    @Override
    public int getOpacity() {
        return 0;
    }


}

完整的源代码：

https://github.com/hiteshsahu/Arc-Drawable

Answer 7

首先，我们需要从起始角度和后掠角度视觉化坐标，然后它将变得更加清晰。

因此，如果您只想要圆的右上角，我们可以做这样的事情：

2N*2N

..

从270度开始（按照上图，向前“倾斜” 90度。您将得到以下形状：

再创建一个，这样您就可以掌握它了。这次让我们使用负值：我们要从右侧开始创建半月形（弧）：

 val rect = RectF(0f, 0f, 500f, 300f)
        val paint = Paint()
        paint.apply {
            strokeWidth = 5f
            setStyle(Paint.Style.STROKE)
            color = COLOR.BLUE
        }
         path.addArc(rect, 270f, 90f)

在这里，我们从0开始并“扫过” -180度。结果是：

如何在画布上的两点之间绘制圆弧？

7 个答案: