namespace LineAndPolygon
{
public partial class Form1 : Form
{
private Point lastPoint = new Point(-1, -1);
private List alPoints; //save all vertex of polygon
private IEnumerator enumerator;
private Region areaRegion = null;
private GraphicsPath areaPath = null;
//test if pp is in the polygon
Point[] pp = { new Point(81, 24), new Point(200, 158) };
//m_Bitmap1 store the opened image info
Bitmap m_Bitmap1 = new Bitmap(2, 2);

public Form1()
{
InitializeComponent();
alPoints = new List();

}

protected GraphicsPath AreaPath
{
get
{
return areaPath;
}
set
{
areaPath = value;
}

}

protected Region AreaRegion
{
get
{
return areaRegion;
}
set
{
areaRegion = value;
}
}
///
/// 判断点是否在多边形内
///
///
///
private bool PointInObject(Point point)
{
return AreaRegion.IsVisible(point);
}
private void CreateObject()
{
if (AreaPath != null)
return;
AreaPath = new GraphicsPath();
int x1 = 0, y1 = 0;
int x2, y2;
enumerator = alPoints.GetEnumerator();
if (enumerator.MoveNext()) //point to the first value
{
x1 = ((Point)enumerator.Current).X;
y1 = ((Point)enumerator.Current).Y;
}
while(enumerator.MoveNext())
{
x2 = ((Point)enumerator.Current).X;
y2 = ((Point)enumerator.Current).Y;
AreaPath.AddLine(x1, y1, x2, y2);
x1 = x2;
y1 = y2;
}
AreaPath.CloseFigure();
AreaRegion = new Region(AreaPath);
}

private void panel1_MouseDown(object sender, MouseEventArgs e)
{

Graphics g = panel1.CreateGraphics();
//Random rand = new Random();
//int rc = rand.Next(255);
//int gc = rand.Next(255);
//int bc = rand.Next(255);

if (e.Button == MouseButtons.Left &&　this.radioButton1.Checked)
{
g.FillRectangle(new SolidBrush(Color.Black), e.X, e.Y, 5, 5);

if (lastPoint.X != -1 && lastPoint.Y != -1)
{
g.DrawLine(new Pen(new SolidBrush(Color.Red)),
lastPoint, new Point(e.X, e.Y));
}

lastPoint.X = e.X;
lastPoint.Y = e.Y;
alPoints.Add(lastPoint);
}
else if (e.Button == MouseButtons.Right && this.radioButton1.Checked)
{

Point[] points = alPoints.ToArray();
//if (rand.Next(1) == 0)
//{
g.DrawPolygon(new Pen(new SolidBrush(
Color.FromArgb(0, 255, 0))), points);
//}
//else
//{
// g.FillPolygon(new SolidBrush(Color.FromArgb(rc, gc, bc)),points);

//}
// alPoints.Clear();
lastPoint.X = -1;
lastPoint.Y = -1;
CreateObject();
testPoint(pp);
alPoints.Clear();
}
// g.Dispose();
}
public void testPoint(Point[] pp)
{
////i :图像的行，j： 图像列，则有pp.y=i,pp.x=j; pp.length=i*img.width+j;

for (int k = 0; k < pp.Length; k++)
{
if (PointInObject(pp[k]))
{

MessageBox.Show(” pp["+k.ToString()+"] is in the polygon”);
label1.Text = Convert.ToString(k);

}
else
{
MessageBox.Show(” pp[" + k.ToString() + "] is not in the polygon”);
label1.Text = “none point in”;
}

}
label1.Text = “”;
}
private void button1_Click(object sender, EventArgs e)
{

openFileDialog1.Filter = “Bitmap文件(*.bmp)|*.bmp| Jpeg文件(*.jpg)|*.jpg| 所有合适文件(*.bmp/*.jpg)|*.bmp/*.jpg”;
if(DialogResult.OK == openFileDialog1.ShowDialog())
{
m_Bitmap1 = (Bitmap)Bitmap.FromFile(openFileDialog1.FileName, false);
}

////获得图像个分量的像素值
for (int k = 0; k < m_Bitmap1.Width * m_Bitmap1.Height; k++)
{
// for (int i = 0; i < m_Bitmap1.Height; i++)
// {
// for (int j = 0; j < m_Bitmap1.Width; j++)
// {
// positonPoint[k] = new Point(i, j);
// pixelValue = m_Bitmap1.GetPixel(i, j);
// rValue = pixelValue.R;
// gValue = pixelValue.G;
// bValue = pixelValue.B;
// }

// }
}

//panel1.Invalidate();
//panel1.Refresh();
Graphics g = panel1.CreateGraphics();
g.DrawImage(m_Bitmap1, new Point(0, 0));
//g.Dispose();
}

PolygonF poly = new PolygonF(POINTF_ARRAY);
if (poly.Contains(SOME_POINTF))
{
…
}

And it works in our production code every time, millions of calls in a single thread execution.

This is a very complex application, and there is a lot of code prior to this that sets up the POINTF_ARRAY, taking into consideration adjustments for margins, padding, available size, centering, etc. In the end, there are a few things that I think are critical. First, all the points are in positive space. Mathematically speaking, this probably shouldn’t matter, but I know in positive space it always works. Second, the points are added to the array in the correct order, ensuring that the proper shape is represented.

This is a great time to try some Unit Testing! I added a Test project to my Solution, used TestInitialize to create a PolygonF object, and then wrote a test method to test various points. Here is a simple example:

[TestInitialize()]
public void MyTestInitialize()
{
List pointList = new List ()
{
new PointF(10, 10),
new PointF(10, 20),
new PointF(20, 20),
new PointF(20, 10)
};

PolyF = new PolygonF(pointList.ToArray());
}

[TestMethod]
public void PolygonContainsPoint()
{
Assert.IsTrue(PolyF.Contains(new PointF(15,15)));
}

Simply change this last point around to test within/without responses. While this example is a simple square, this code is currently funcitoning with some fairly complex non-symmetrical polygons, up to 20 sides (a limit of our application, not this class). ]]> http://www.developingfor.net/c-20/testing-to-see-if-a-point-is-within-a-polygon.html/comment-page-1#comment-119 batterfly Fri, 27 Jun 2008 04:08:08 +0000 http://www.developingfor.net/net-20/testing-to-see-if-a-point-is-within-a-polygon.html#comment-119 hi , i wrote a code about drawing polygon ,and judge some points if there are in or not in the polygon using c# ,but the result is very different , some times the judge is right ,some times it is wrong to the same situation ,i don't kown why . and i need your help,ple leave a email ,so that i can send it to you. thank you hi ,
i wrote a code about drawing polygon ,and judge some points if there are in or not in the polygon using c# ,but the result is very different , some times the judge is right ,some times it is wrong to the same situation ,i don’t kown why . and i need your help,ple leave a email ,so that i can send it to you.
thank you