Develop Reference

How do I determine the rotation point of a polygon (triangle)?

I would like to draw a thick, transparent arrow with an arrowhead:
Here's the code that draws the arrow shaft. Notice that I have to offset the rectangle so the calculations are done from the midpoint of the rectangle.
private void DrawMovementArrow(bool color, double StartX, double StartY, double EndX, double EndY)
{
SolidColorBrush partiallyTransparentSolidColorBrush;
Rectangle myRectangle = new Rectangle();
// This will be replaced by piece size
int width = 35;
myRectangle.Width = width;
// Apparently necessary to offset the drawing of the path so that the point is in the center of the path; not the edge.
StartX -= width / 2;
EndX -= width / 2;
myRectangle.Height = Map.EuclideanDistance(StartX, StartY, EndX, EndY) ;
int angle = CalculateAngle(StartX , StartY , EndX , EndY );
// This selects the midpoint of edge of the rectangle to rotate around (weird system)
myRectangle.RenderTransformOrigin = new Point(0.5, 0);
angle = angle - 180;
RotateTransform rotateTransform1 = new RotateTransform(angle, 0 , 0 );
myRectangle.RenderTransform = rotateTransform1;
if (color)
partiallyTransparentSolidColorBrush = new SolidColorBrush(Colors.Blue);
else
partiallyTransparentSolidColorBrush = new SolidColorBrush(Colors.Red);
partiallyTransparentSolidColorBrush.Opacity = 0.4;
myRectangle.Fill = partiallyTransparentSolidColorBrush;
MovementCanvas1.Children.Clear();
MovementCanvas1.Children.Add(myRectangle);
Canvas.SetTop(myRectangle, StartY);
Canvas.SetLeft(myRectangle, StartX);
DrawArrowhead(color, EndX, EndY, angle + 90, width);
ShowUnitCenter(MovementArrowList[0]);
}
Note that this code selects a point in the middle of the edge to rotate the rectangle:
// This selects the midpoint of edge of the rectangle to rotate around (weird system)
myRectangle.RenderTransformOrigin = new Point(0.5, 0);
The problem is that I can't find that point with the arrowhead (triangle). Here's the code that draws the arrowhead:
public void DrawArrowhead(bool color, double x, double y, int angle, int width)
{
x += width /2 ;
width = width + (width / 2);
//Add the Polygon Element
Polygon myPolygon = new Polygon();
myPolygon.Opacity = 0.4;
if (color)
{
myPolygon.Fill = new SolidColorBrush(Colors.Blue);
myPolygon.Stroke = System.Windows.Media.Brushes.Blue;
}
else
{
myPolygon.Fill = new SolidColorBrush(Colors.Red);
myPolygon.Stroke = System.Windows.Media.Brushes.Red;
}
myPolygon.StrokeThickness = 0;
RotateTransform rotateTransform1 = new RotateTransform(angle, 0, 0);
myPolygon.RenderTransform = rotateTransform1;
// This selects the midpoint of edge of the triangle to rotate around (weird system)
myPolygon.RenderTransformOrigin = new Point(0.0, 0.5);
System.Windows.Point Point1 = new System.Windows.Point(0, 0);
System.Windows.Point Point2 = new System.Windows.Point(width / 2, width / 2);
System.Windows.Point Point3 = new System.Windows.Point(0,width);
PointCollection myPointCollection = new PointCollection();
myPointCollection.Add(Point1);
myPointCollection.Add(Point2);
myPointCollection.Add(Point3);
myPolygon.Points = myPointCollection;
MovementCanvas1.Children.Add(myPolygon);
Canvas.SetTop(myPolygon, y );
Canvas.SetLeft(myPolygon, x );
}
Note the myPointCollection that creates the triangle. The problem is that I've tried almost every conceivable combination of values in RenderTransformOrigin to find the point that (center bottom of triangle) to use for the rotation point. Nothing seems to be working out.
Can anybody suggest the correct value?
Edit Solved
I solved it by changing the points of the triangle. That was easier than trying to figure out the rotation point.

Changing the points that made up the triangle solved the problem. This was easier than trying to find the rotation point.

C# merge two rotated bitmaps

I am trying to rotate two bitmaps, then copy the results into a third one.
Bitmap bmp_1 = new Bitmap(Program.Properties.Resources.MyImage); // 100x100 px
Bitmap bmp_2 = new Bitmap(Program.Properties.Resources.MyImage); // 100x100 px
Bitmap bmp_merged = new Bitmap(200, 100, PixelFormat.Format32bppArgb);
float angle, bw2, bh2;
using (Graphics g = Graphics.FromImage(bmp_merged))
{
using (Graphics graphics = Graphics.FromImage(bmp_1))
{
angle = 15;
bw2 = bmp_1.Width / 2f;
bh2 = bmp_1.Height / 2f;
graphics.TranslateTransform(bw2, bh2);
graphics.RotateTransform(angle);
graphics.TranslateTransform(-bw2, -bh2);
graphics.DrawImage(bmp_1, 0, 0);
}
using (Graphics graphics = Graphics.FromImage(bmp_2))
{
angle = 35;
bw2 = bmp_2.Width / 2f;
bh2 = bmp_2.Height / 2f;
graphics.TranslateTransform(bw2, bh2);
graphics.RotateTransform(angle);
graphics.TranslateTransform(-bw2, -bh2);
graphics.DrawImage(bmp_2, 0, 0);
}
g.DrawImage(bmp_1, 0, 0);
g.DrawImage(bmp_2, 100, 0);
}
Issue:
After using graphics.DrawImage(bmp_1, 0, 0); I expected that bmp_1 will be a rotated image.
But it's actually the original bmp_1 image and its rotated version drawn over it.

Drawing into a Graphics object obtained from a Bitmap instance doesn't clear the Bitmap instance first. It just draws on top of whatever was there.
Instead of modifying the bitmaps you start with, you should just draw them rotated into the destination. For example, something like this:
using (Graphics g = Graphics.FromImage(bmp_merged))
{
angle = 15;
bw2 = bmp_1.Width / 2f;
bh2 = bmp_1.Height / 2f;
g.TranslateTransform(bw2, bh2);
g.RotateTransform(angle);
g.TranslateTransform(-bw2, -bh2);
g.DrawImage(bmp_1, 0, 0);
angle = 35;
bw2 = bmp_2.Width / 2f;
bh2 = bmp_2.Height / 2f;
g.ResetTransform();
g.TranslateTransform(bw2, bh2);
g.RotateTransform(angle);
g.TranslateTransform(-bw2, -bh2);
g.DrawImage(bmp_2, 0, 0);
}
Naturally, you should really factor the code for drawing a bitmap rotated at a specific angle out into its own method, so that you don't have two copies of the code. But the above should address your basic problem.

Drawing a polygon according to the input coordinates

How can i draw a polygon according to the input coordinates which are given in C#.

You didn't show any code because based on those coordinate, you are applying some form of scaling to the image.
Using the Paint event of a PictureBox, here is an example using those coordinates on the screen. It fills in the polygon, then draws the border, then it loops through all the points to draw the red circle:
void pictureBox1_Paint(object sender, PaintEventArgs e) {
e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
e.Graphics.Clear(Color.White);
// draw the shading background:
List<Point> shadePoints = new List<Point>();
shadePoints.Add(new Point(0, pictureBox1.ClientSize.Height));
shadePoints.Add(new Point(pictureBox1.ClientSize.Width, 0));
shadePoints.Add(new Point(pictureBox1.ClientSize.Width,
pictureBox1.ClientSize.Height));
e.Graphics.FillPolygon(Brushes.LightGray, shadePoints.ToArray());
// scale the drawing larger:
using (Matrix m = new Matrix()) {
m.Scale(4, 4);
e.Graphics.Transform = m;
List<Point> polyPoints = new List<Point>();
polyPoints.Add(new Point(10, 10));
polyPoints.Add(new Point(12, 35));
polyPoints.Add(new Point(22, 35));
polyPoints.Add(new Point(24, 22));
// use a semi-transparent background brush:
using (SolidBrush br = new SolidBrush(Color.FromArgb(100, Color.Yellow))) {
e.Graphics.FillPolygon(br, polyPoints.ToArray());
}
e.Graphics.DrawPolygon(Pens.DarkBlue, polyPoints.ToArray());
foreach (Point p in polyPoints) {
e.Graphics.FillEllipse(Brushes.Red,
new Rectangle(p.X - 2, p.Y - 2, 4, 4));
}
}
}

You may use Graphics.DrawPolygon. You can store the coordinates in an array of Point and then you can pass that to DrawPolygon method. You may wanna see:
Drawing with Graphics in WinForms using C#
private System.Drawing.Graphics g;
System.Drawing.Point[] p = new System.Drawing.Point[6];
p[0].X = 0;
p[0].Y = 0;
p[1].X = 53;
p[1].Y = 111;
p[2].X = 114;
p[2].Y = 86;
p[3].X = 34;
p[3].Y = 34;
p[4].X = 165;
p[4].Y = 7;
g = PictureBox1.CreateGraphics();
g.DrawPolygon(pen1, p);

This simple function is able to generate an array of PointF equal to the vertices of the regular polygon to be drawn, where "center" is the center of the polygon, "sides" is its number of sides, "sideLength" is the size of each side in pixels and "offset" is its slope.
public PointF[] GetRegularPolygonScreenVertex(Point center, int sides, int sideLength, float offset)
{
var points = new PointF[sides];
for (int i = 0; i < sides; i++)
{
points[i] = new PointF(
(float)(center.X + sideLength * Math.Cos((i * 360 / sides + offset) * Math.PI / 180f)),
(float)(center.Y + sideLength * Math.Sin((i * 360 / sides + offset) * Math.PI / 180f))
);
}
return points;
}
The result obtained can be used to draw a polygon, e.g. with the function:
GraphicsObject.DrawPolygon(new Pen(Brushes.Black, GetRegularPolygonScreenVertex(new Point(X, Y), 6, 30, 60f));
Which will generate a regular hexagon with a side of 30 pixels inclined by 30°.
hex

Filling Color in a hexagon in WPF

I'm having problem in filling the hexagon using this code, when this code runs it draws only the outline of the hexagon that is "White", I want to fill the hexagon with a color but it is not working.
I have searched a lot and tried many things like drawingContext.Drawing() , drawingBrush, etc.
Am I missing something in this code? This is the code:
public void DrawHexagon(DrawingContext drawingContext)
{
GeometryGroup hexaKey = new GeometryGroup();
//making lines for hexagon
hexaKey.Children.Add(
new LineGeometry(new Point(X1, Y1), new Point(X2, Y2)));
hexaKey.Children.Add(
new LineGeometry(new Point(X2, Y2), new Point(X3, Y3)));
hexaKey.Children.Add(
new LineGeometry(new Point(X3, Y3), new Point(X4, Y4)));
hexaKey.Children.Add(
new LineGeometry(new Point(X4, Y4), new Point(X5, Y5)));
hexaKey.Children.Add(
new LineGeometry(new Point(X5, Y5), new Point(X6, Y6)));
hexaKey.Children.Add(
new LineGeometry(new Point(X6, Y6), new Point(X1, Y1)));
//
// Create a GeometryDrawing.
//
GeometryDrawing hexaKeyDrawing = new GeometryDrawing();
hexaKeyDrawing.Geometry = hexaKey;
// Paint the drawing with a gradient.
hexaKeyDrawing.Brush =new SolidColorBrush(Colors.Red);
// Outline the drawing with a solid color.
hexaKeyDrawing.Pen = new Pen(Brushes.White, 2);
drawingContext.DrawGeometry(hexaKeyDrawing.Brush, hexaKeyDrawing.Pen, hexaKeyDrawing.Geometry);
}

LineGeometry doesn't have a way to fill... they're just lines. You need a path. The MSDN has an example

An example, how to fill hexagons: http://www.codeproject.com/Articles/14948/Hexagonal-grid-for-games-and-other-projects-Part-1

In your example you have a number of LineGeometry instances inside a GeometryGroup inside a GeometryDrawing.
First, I'd link to bring to your attention that you're not actually using the GeometryDrawing. In your example you've used it solely as a place holder for your GemetryGroup.
Ignoring this the problem is that LineGeometry instances were not intended to draw shapes and GeometryGroup is not able to realize that your 6 LineSegments together form a closed shape.
Despair not however as there is a way to accomplish what you want: PathGeometry. This geometry essentially defines the contour of a region that may be filled! This contour may is defined by a starting point and a series of PathSegments.
private Point GetExtremity(Point center, double radius, double orientation)
{
return new Point(
center.X + Math.Cos(orientation) * radius,
center.Y + Math.Sin(orientation) * radius
);
}
public void DrawUniformShape(DrawingContext context, Brush brush, Pen pen, Point center, double radius, int sides, double orientationRadians)
{
context.DrawGeometry(
brush,
pen,
new PathGeometry(
Enumerable.Repeat(
new PathFigure(
GetExtremity(center, radius, orientationRadians),
from vertex in Enumerable.Range(1, sides - 1)
let angle = orientationRadians + vertex * 2 * Math.PI / sides
select new LineSegment(GetExtremity(center, radius, angle), true),
true
),
1
)
)
);
}
public void DrawBarnColouredHexagon(DrawingContext context, Point center, double radius, double orientation)
{
DrawUniformShape(
context,
Brushes.Red,
new Pen(Brushes.White, 2),
center,
radius,
6,
0
);
}

c# drawing text over an object

i am drawing a dashed line over an object using this method:
// Get Graphics object from chart
Graphics graph = e.ChartGraphics.Graphics;
PointF point1 = PointF.Empty;
PointF point2 = PointF.Empty;
// Set Maximum and minimum points
point1.X = -110;
point1.Y = -110;
point2.X = 122;
point2.Y = 122;
// Convert relative coordinates to absolute coordinates.
point1 = e.ChartGraphics.GetAbsolutePoint(point1);
point2 = e.ChartGraphics.GetAbsolutePoint(point2);
// Draw (dashed) connection line
float[] dashValues = { 4, 2 };
Pen dashPen= new Pen(Color.Yellow, 3);
dashPen.DashPattern = dashValues;
graph.DrawLine(dashPen, point1, point2);
and i would like to know whether it is possible to write text over an object the same way/.??

You should look at the DrawString method.

Yes you can accomplish this in Graphics.DrawString