c# - GraphicsPath.AddArc 如何使用 startAngle 和 sweepAngle 参数？

Question

我正在尝试使用 System.Drawing.Drawing2D.GraphicsPath.AddArc 绘制从 0 度开始并扫描到 135 度的椭圆弧。

我遇到的问题是，对于椭圆，绘制的圆弧与我的预期不符。

例如，下面的代码生成下图。绿色圆圈是我希望圆弧的终点使用椭圆上的点的公式的地方。我的公式适用于圆但不适用于椭圆。

这与极坐标与笛卡尔坐标有关吗？

    private PointF GetPointOnEllipse(RectangleF bounds, float angleInDegrees)
    {
        float a = bounds.Width / 2.0F;
        float b = bounds.Height / 2.0F;

        float angleInRadians = (float)(Math.PI * angleInDegrees / 180.0F);

        float x = (float)(( bounds.X + a ) + a * Math.Cos(angleInRadians));
        float y = (float)(( bounds.Y + b ) + b * Math.Sin(angleInRadians));

        return new PointF(x, y);
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        Rectangle circleBounds = new Rectangle(250, 100, 500, 500);
        e.Graphics.DrawRectangle(Pens.Red, circleBounds);

        System.Drawing.Drawing2D.GraphicsPath circularPath = new System.Drawing.Drawing2D.GraphicsPath();
        circularPath.AddArc(circleBounds, 0.0F, 135.0F);
        e.Graphics.DrawPath(Pens.Red, circularPath);

        PointF circlePoint = GetPointOnEllipse(circleBounds, 135.0F);
        e.Graphics.DrawEllipse(Pens.Green, new RectangleF(circlePoint.X - 5, circlePoint.Y - 5, 10, 10));

        Rectangle ellipseBounds = new Rectangle(50, 100, 900, 500);
        e.Graphics.DrawRectangle(Pens.Blue, ellipseBounds);

        System.Drawing.Drawing2D.GraphicsPath ellipticalPath = new System.Drawing.Drawing2D.GraphicsPath();
        ellipticalPath.AddArc(ellipseBounds, 0.0F, 135.0F);
        e.Graphics.DrawPath(Pens.Blue, ellipticalPath);

        PointF ellipsePoint = GetPointOnEllipse(ellipseBounds, 135.0F);
        e.Graphics.DrawEllipse(Pens.Green, new RectangleF(ellipsePoint.X - 5, ellipsePoint.Y - 5, 10, 10));
    }

Answer 1

我对 GraphicsPath.AddArc 的工作原理感到困惑，我找不到任何像样的图表，所以我画了一个。以防其他人遭受同样的痛苦! http://imgur.com/lNBewKZ