在圆弧的起点和终点画圆

Question

嗨，我在圆弧的两端（起点和终点）画点有困难

虽然我可以在canvas上画弧线。这是我绘制圆弧的示例代码。

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    float width = (float) getWidth();
    float height = (float) getHeight();
    float radius;

    if (width > height) {
        radius = height / 4;
    } else {
        radius = width / 4;
    }

    float center_x, center_y;
    final RectF oval = new RectF();

    center_x = width / 2;
    center_y = height / 2;

    oval.set(center_x - radius,
            center_y - radius,
            center_x + radius,
            center_y + radius);

    float percent = 25;
    float arcRadius = 360;
    float angle = arcRadius * (percent/100);

    canvas.drawArc(oval, 270, 360, false, trackpaint);
    canvas.drawArc(oval, 270, angle, false, arcPaint);  
}

唯一缺少的是在圆弧的起点和终点放置圆圈。我试过这个 link 但确实有效 Calculate Arc Center Point, Knowing It's Start and End Degrees。任何帮助都感激不尽。谢谢

Answer 1

起点坐标为：

double startX = Math.cos(Math.toRadians(270)) * radius + center_x;

double startY = Math.sin(Math.toRadians(270)) * radius + center_y;

终点坐标为：

double endX = Math.cos(Math.toRadians(270 + angle)) * radius + center_x;

double endY = Math.sin(Math.toRadians(270 + angle)) * radius + center_y;

然后可以用起点和终点画圆：

canvas.drawCircle(startX, startY, 10, paint);

canvas.drawCircle(endX, endY, 10, paint);

Answer 2

从 ARC 获取路径
使用 PathMeasure class 检索路径长度和路径 TAN，使用 ARC 的起始或结束 X 和 Y 坐标
使用此 X 和 Y 坐标绘制圆。

ARC 开头的圆示例：

final Path mPath = new Path();
mPath.addArc(oval, startAngle, sweepAngle);
PathMeasure pm = new PathMeasure(mPath, false);
float[] xyCoordinate = { arcStarting.x , arcStarting.y };
float pathLength = pm.getLength();
pm.getPosTan(0, xyCoordinate, null);//"0 for starting point"
PointF point = new PointF(xyCoordinate[0], xyCoordinate[1]);
canvas.drawCircle(point.x, point.y, 10, YourPaintHere)

在圆弧的起点和终点画圆

Draw circle on start and end point of an Arc

android

view

draw

android-custom-view

ondraw