Draw custom ellipse in winform

In System.Drawing and System.Drawing.Drawing2D, I can only draw horizontal or vertical shape. Now i want to draw custom shape.

Given the coordinate of points A, B, C, D. I want to draw an ellipse like the blue one in the picture.

回答1:

The example below is taken from MSDN:

private void RotateTransformAngle(PaintEventArgs e)
{
    // Set world transform of graphics object to translate.
    e.Graphics.TranslateTransform(100.0F, 0.0F);

    // Then to rotate, prepending rotation matrix.
    e.Graphics.RotateTransform(30.0F);

    // Draw rotated, translated ellipse to screen.
    e.Graphics.DrawEllipse(new Pen(Color.Blue, 3), 0, 0, 200, 80);
}

回答2:

The correct solution involves:

Calculating the center
using Graphics.TranslateTransform to move the center to the origin
Calculating the Size and the Location of the bounding Rectangle
using Graphics.RotateTransform to rotate the canvas
Drawing the ellipse with Graphics.DrawEllipse
Resetting the Graphcis object

This does take a little Math but will produce real and fine ellipses..

For fun you also may want to play with a cheap, fake solution: I uses the DrawClosedCurve method with a tension.

To test I added a TrackBar set with a Maximum of 100.

Values of around 80, i.e. Tensions of around 0.8f create pretty nice ellipsoids:

private void panel1_Paint(object sender, PaintEventArgs e)
{
    List<Point> points1 = new List<Point>()
    { new Point(300, 100), new Point(500, 300), new Point(400, 500), new Point(200, 300) };

    List<Point> points2 = new List<Point>() 
    { new Point(100, 100), new Point(500, 100), new Point(500, 400), new Point(100, 400) };

    e.Graphics.DrawClosedCurve(Pens.Red, points1.ToArray(), 
        (float)(trackBar1.Value / 100f), System.Drawing.Drawing2D.FillMode.Alternate);

    e.Graphics.DrawClosedCurve(Pens.Blue, points2.ToArray(), 
        (float)(trackBar1.Value / 100f), System.Drawing.Drawing2D.FillMode.Alternate);
}