Develop Reference

how to draw polygon including negative points ? in C#

i am doing c# project. i have found a problem and unable to find answer of this problem that's why i am posting here/
i am implementing procedural floor plan generation in c#. at first i need to draw a polygon to on given points to generate grid. points can be positive or negative. points will be in floating.
From the Microsoft Documentation i am able to draw polygon for the floating positive points, but when i change points to negative it does not draw anything on form.
this method id drawing x,y coordinates 0,0 in the corner .
code example
public void DrawPolygonPointF(PaintEventArgs e)
{
// Create pen.
Pen blackPen = new Pen(Color.Black, 3);
// Create points that define polygon.
PointF point1 = new PointF(50.0F, 50.0F);
PointF point2 = new PointF(100.0F, 25.0F);
PointF point3 = new PointF(200.0F, 5.0F);
PointF point4 = new PointF(250.0F, 50.0F);
PointF point5 = new PointF(300.0F, 100.0F);
PointF point6 = new PointF(350.0F, 200.0F);
PointF point7 = new PointF(250.0F, 250.0F);
PointF[] curvePoints =
{
point1,
point2,
point3,
point4,
point5,
point6,
point7
};
// Draw polygon curve to screen.
e.Graphics.DrawPolygon(blackPen, curvePoints);
}
i have negative coordinates value for example pointF(300,-250) this method is not drawing nothing for negative coordinates value.
So please give me brief solution because i don't know much about drawing.
Thank you

In C# 0,0 is the top left corner of the screen. So negative values are off the left or top edge of your form. You need to transform your coordinates from your coordinate space to the form's. To place 0,0 dead center, you would do this:
int screenX = myX + windowWidth / 2;
int screenY = myY + windowHeight / 2;

Building off of the answer #pquest gave, and your newly added sample code, doing a "real" GDI transformation would look like this:
// Create pen.
Pen blackPen = new Pen(Color.Black, 3);
// Create points that define polygon.
PointF point1 = new PointF(50.0F, 50.0F);
PointF point2 = new PointF(100.0F, 25.0F);
PointF point3 = new PointF(200.0F, 5.0F);
<...snip...>
//Apply a translation Transformation to move 0,0 to the center of the
//window. You can now draw your points with negative values, without doing
//any addition to them.
int screenX = windowWidth / 2;
int screenY = windowHeight / 2;
e.Graphics.TranslateTransform((float) screenX, (float) screenY);
// Draw polygon curve to screen.
e.Graphics.DrawPolygon(blackPen, curvePoints);
GDI Transformations are very powerful. You can use them to move points around, flip points horizontally or vertically, scale things bigger or smaller, distort like a parallelogram, and even do rotations. All of these can be combined in to what is called a transformation matrix to get some very cool results.
More examples can be found on MSDN.

That's working for me to this problem.
you just need to add couple lines of code in your code.
int windowWidth = this.ClientSize.Width;
int windowHeight = this.ClientSize.Height;
int screenX = windowWidth / 2;
int screenY = windowHeight / 2;
e.Graphics.TranslateTransform((float)screenX, (float)screenY);

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.

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);
}

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);
}

How can I draw a circle with antialiasing and gaussian line intensity using EmguCV (OpenCV)?

I need to draw the most perfect circle possible. EmguCV seems to lack an anti-aliasing option.
I'm trying to use SmoothGaussian, but the circle still does not look good/smooth enough.
Also, the circle line intensity should have Gaussian shape (i.e.: brighter in the center).
How can I achieve that?
Here is what I'm doing now:
using (Image<Gray, Byte> img = new Image<Gray, byte>(800, 800, new Gray(0)))
{
PointF center = new PointF(img.Width / 2, img.Height / 2);
//Center line
float r = 200.0f;
CircleF circle = new CircleF(center, r);
img.Draw(circle, new Gray(255), 1);
img._SmoothGaussian(7, 7, 3, 3);
}

If you use Brg, Brga or Gray color you can use that hack:
using(var graph = Graphics.FromImage(image.Bitmap))
{
graph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
graph.DrawEllipse(new Pen(color.BackColor), x, y, d`i`ameter, diameter);
}
`
Edit:
You can also use cvInvoke
var center = new Point(x, y);
var color = new Bgr(this.color.BackColor);
CvInvoke.cvCircle(image.Ptr, center, radius, color.MCvScalar, thickness, Emgu.CV.CvEnum.LINE_TYPE.CV_AA, 0);
`

Centering rotated graphicPath using the Matrix object in C#

I am writing a library that will create a graphihc path (In the shape of a polygon or rectangle) and rotate it but I want the rotated shape to be centered within its bounding rectangle. I have tried almost everything to get the shape to rotate on its center but it cutting off at the edges.
Below is some smaple code I have written to try to accomplish this
GraphicsPath path = new GraphicsPath();
path.AddPolygon(new Point[] { new Point(0, 0), new Point(100, 0), new Point(100, 100), new Point(0, 100) });
Matrix m = new Matrix();
Matrix m2 = new Matrix();
m2.Rotate(30);
m.Translate(-((path.GetBounds(m2).Width) / 2), -((path.GetBounds(m2).Height) / 2));
m.Rotate(30, MatrixOrder.Append);
m.Translate(((path.GetBounds(m2).Width)/2), ((path.GetBounds(m2).Height)/2), MatrixOrder.Append);
path.Transform(m);
Bitmap b = new Bitmap((int)path.GetBounds().Width, (int)path.GetBounds().Height);
Graphics g = Graphics.FromImage(b);
g.FillPath(Brushes.Blue, path);
b.Save(#"c:\aSSETS\sample3.png");
Please help. Thanks

c# can you get position from axis without having a form?

I have a WinForm application that I would like to convert to a service. It has two mscharts on it. I don't need to see those charts anymore because the application creates bitmaps out of them. I am drawing a line on one chart depending on data from another chart, like this:
// Get Graphics object from chart
Graphics graph = e.ChartGraphics.Graphics;
// Convert X and Y values to screen position
float pixelYMax = (float)e.ChartGraphics.GetPositionFromAxis("Default", AxisName.Y, CreatininePoint.YValues[0]);
float pixelXMax = (float)e.ChartGraphics.GetPositionFromAxis("Default", AxisName.X, CreatininePoint.XValue);
float pixelYMin = (float)e.ChartGraphics.GetPositionFromAxis("Default", AxisName.Y, CreatininePoint.YValues[0]-20);
float pixelXMin = (float)e.ChartGraphics.GetPositionFromAxis("Default", AxisName.X, CreatininePoint.XValue);
PointF point1 = PointF.Empty;
PointF point2 = PointF.Empty;
// Set Maximum and minimum points
point1.X = pixelXMax;
point1.Y = pixelYMax-10;
point2.X = pixelXMin;
point2.Y = 84;
// Convert relative coordinates to absolute coordinates.
point1 = e.ChartGraphics.GetAbsolutePoint(point1);
point2 = e.ChartGraphics.GetAbsolutePoint(point2);
float[] dashValues = { 4,2 };
Pen blackPen = new Pen(Color.Black, 1);
blackPen.DashPattern = dashValues;
//e.Graphics.DrawLine(blackPen, new Point(5, 5), new Point(405, 5));
//graph.DrawLine(blackPen, point1, point2);
// Draw connection line
graph.DrawLine(new Pen(Color.Black, 2), point2, point1);
// Create string to draw.
//String drawString = creatininept + " ng/mL";
String drawString = "67 ng/mL";
// Create font and brush.
Font drawFont = new Font("Arial", 7);
SolidBrush drawBrush = new SolidBrush(Color.Black);
// Create point for upper-left corner of drawing.
PointF drawPoint = new PointF(point1.X,point1.Y+5);
// Draw string to screen.
graph.DrawString(drawString, drawFont, drawBrush, drawPoint);
is it possible to do this without having a form so that we can have a service running?

Bitmap canvas = new Bitmap(600, 480);
Graphics graph = Graphics.FromImage(canvas);
.. then proceed with drawing on graph.