Develop Reference

How to paint a certain area

I am new to drawing and paints in c# & I am trying to make a simple program it has 3 intersecting circles (A,B,C). What i want to do is paint a certain (according to result I get).
For example: If I get 1 as a result I want to fill the yellow bordered region, if I get 4 I want to fill green bordered region and so on.
My Code to draw these circles:
private void button1_Click(object sender, EventArgs e)
{
Graphics A = this.CreateGraphics();
Graphics B = this.CreateGraphics();
Graphics C = this.CreateGraphics();
Pen Bluepen = new Pen(Color.Blue, 2);
Pen RedPen = new Pen(Color.Red, 2);
Pen BlackPen = new Pen(Color.Black, 2);
A.DrawEllipse(Bluepen,100, 100, 150, 150);
B.DrawEllipse(RedPen, 195, 100, 150, 150);
C.DrawEllipse(BlackPen, 145, 190, 150, 150);
}

Since you are new to this topic I have to tell you: This is a lot harder that one would hope for.
Three solutions come to mind:
Construct a GraphicsPath you could fill from three Arcs. To calculate the arcs you need the rectangles you have but also the sweeping angle and also the starting angle. This will take quite some math..
After having drawn into a Bitmap you could floodfill the area you want to color. This will only work for bitamps from which you can extract the current color of each pixel, not for drawing onto controls..
The simplest way it still a bit involved, but only mildly so
Solution 3 (Create a Region and fill it)
You can use all sorts of set operations to combine areas called Regions. And you can construct a Region from a GraphicsPath. And you can construct a GraphicsPath by adding an ellipse. And you can clip the drawing area of a Graphics object to a Region.
Let's try:
private void panel1_Paint(object sender, PaintEventArgs e)
{
Graphics g = e.Graphics;
g.SmoothingMode = SmoothingMode.AntiAlias;
Rectangle r1 = new Rectangle(100, 100, 150, 150);
Rectangle r2 = new Rectangle(195, 100, 150, 150);
Rectangle r3 = new Rectangle(145, 190, 150, 150);
GraphicsPath gp1 = new GraphicsPath();
GraphicsPath gp2 = new GraphicsPath();
GraphicsPath gp3 = new GraphicsPath();
gp1.AddEllipse(r1);
gp2.AddEllipse(r2);
gp3.AddEllipse(r3);
Region r_1 = new Region(gp1);
Region r_2 = new Region(gp2);
Region r_3 = new Region(gp3);
r_1.Intersect(r_2); // just two of five..
r_1.Exclude(r_3); // set operations supported!
g.SetClip(r_1, CombineMode.Replace);
g.Clear(Color.Magenta); // fill the remaining region
g.ResetClip();
g.DrawEllipse(Pens.Red, r1);
g.DrawEllipse(Pens.Blue, r2);
g.DrawEllipse(Pens.Green, r3);
// finally dispose of all Regions and GraphicsPaths!!
r_1.Dispose();
gp1.Dispose();
.....
}
Do note that the region operations change the current region; if you want to fill more areas you need to restore the changed region!
Also note that I draw where any persistent drawing belongs: In the Paint event and that I use its e.Graphics object..
GraphicsPaths as Regions are GDI objects and should be disposed off!
Notes on solution 1 (Create a GraphicsPath by Math)
The full math is rather involved. By making a few assumptions the task can be greatly simplified: Let's assume the circles have the same size. Also that we first look at two circles only, with the same y-position. Finally that the circles form a symmetrical figure. (Which btw they don't: the red circle should have x=190 and the green one y=186,45..)
Getting the two intersection points as well as the sweeping angle is not so hard.
Next one can rotate the two points twice around the center of the whole figure by 120° using a Matrix; see here for an example. Now we have six points; we still need the smaller sweeping angle, which is also found with simple math.
Finally we can construct all 12 (!) GraphicsPaths from the 12 arcs and combine them at will.
The good part is that we can both fill and draw those paths. But, the code is rather extensive..
Notes on solution 2 (floodfill)
While you can't floodfill directly on a control you can prepare the result in a bitmap and then display that image on the control with Graphics.DrawImage.
For an example of coding a floodfill see this post!

Converting the path of a Rectangle into a GraphicPath/Region

I am learning about GraphicsPath and Region. And using it with Invalidate.
So, I have a Rectangle object and I want to erase this rectangle. But, I only want to erase the edge of the rectangle (that is, the lines).
At the moment I have this:
if(bErase)
{
Rectangle rcRubberBand = GetSelectionRectangle();
GraphicsPath path = new GraphicsPath();
path.AddRectangle(rcLastRubberBand);
Region reg = new Region(path);
myControl3.Invalidate(reg);
myControl3.Update();
}
It works, but it is invalidating the complete rectangle shape. I only need to invalidate the rectangle lines that I had drawn. Can I make such a path with GraphicsPath?

You can't get the system to invalidate anything but a full rectangle.
So you can't use an outline path to save time.
However it can be useful for other things. Let's look at two options :
You can create an outline path
You can exclude parts of a region
The simplest way to create an outline GraphicsPath is to widen a given path with a Pen:
GraphicsPath gp = new GraphicsPath();
gp.AddRectangle(r0);
using (Pen pen = new Pen(Color.Green, 3f)) gp.Widen(pen);
This let's you make use of all the many options of a Pen, including DashStyles, Alignment, LineJoins etc..
An alternative way is to create it with the default FillMode.Alternate and simply add a smaller figure:
Rectangle r0 = new Rectangle(11, 11, 333, 333);
Rectangle r1 = r0;
r1.Inflate(-6, -6);
GraphicsPath gp = new GraphicsPath();
gp.AddRectangle(r0);
gp.AddRectangle(r1);
Now you can fill the path
g.FillPath(Brushes.Red, gp);
or use it to clip the ClipBounds of a Graphics object g :
g.SetClip(gp);
After this anything you draw including a Clear will only affect the pixels inside the outline.
When you are done you can write:
g.ResetClip();
and continue drawing on the full size of your graphics target.
Or you can use the path as the basis for a Region:
Region r = new Region(gp);
and restrict a Control to it..:
somecontrol.Region = r;
Regions support several set operations so instead of using the above outline path you could also write this with the same result:
Region r = new Region(r0);
r.Exclude(r1);

How to draw in c#

I am trying to draw the YinYang symbol on C# windows Form Application. So far, I drew the big outer circle and the two innner circles.
I need help on drawing the curve part that runs down the middle of the circle
Also, how would I fill in the small circle and the other half of the circle to be black.
Also, it is possible to draw this without having to have a button (see code).
Here is a snippet of my code:
private void button1_Click(object sender, EventArgs e)
{
Graphics myGraphics = base.CreateGraphics();
Pen myPen = new Pen(Color.Black);
SolidBrush mySolidBrush = new SolidBrush(Color.Black);
myGraphics.DrawEllipse(myPen, 50,50, 150, 150);
Graphics innerCircle = base.CreateGraphics();
Pen myPen2 = new Pen(Color.Black);
SolidBrush mySolidBrush2 = new SolidBrush(Color.Black);
myGraphics.DrawEllipse(myPen, 118, 75, 20, 20);
Graphics innerCircle2 = base.CreateGraphics();
Pen myPen3 = new Pen(Color.Black);
SolidBrush mySolidBrush3 = new SolidBrush(Color.Black);
myGraphics.DrawEllipse(myPen, 118, 150, 20, 20);
}

You do not have to draw a curve, geometry of ying and yang is so beautiful that it lets you draw it only using circles.
Sorry for my paint skills, but I think you know what I mean by this pic. You said
I drew the big outer circle and the two innner circles.
So use this knowledge again without thinking about curves

Is there a method to draw on the panel in c# which not redraw what i've drawn? E.g. when I use refresh() or Invalidate() alway redraw me it, but I need something what not. :(

Moving a high quality line on a panel c#

I want to draw a line on a panel and then move it as the mouse moves. To do so, I draw the line and when the mouse moves I redraw the line to the new location and remove the previous line by drawing a line with the background color on it. It works fine if I do not use the high quality smoothing mode. But if use high quality smoothing mode, it leave traces on the panel. Does anybody know how to fix this? Thank you.
Here is the code
int x_previous = 0;
int y_previous = 0;
private void panel1_MouseMove(object sender, MouseEventArgs e)
{
Pen pen1 = new System.Drawing.Pen(Color.Black, 3);
Pen pen2 = new System.Drawing.Pen(panel1.BackColor, 3);
Graphics g = panel1.CreateGraphics();
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
g.DrawLine(pen2, new Point(0, 0), new Point(x_previous, y_previous));
g.DrawLine(pen1, new Point(0, 0), new Point(e.Location.X, e.Location.Y));
x_previous = e.Location.X;
y_previous = e.Location.Y;
}
Here is the snapshot with SmoothingMode
Here is the snapshot without SmoothingMode

Instead of drawing a line over a line, the safest option would be to clear the graphics using g.Clear(panel1.BackColor). This will wipe everything off that has been drawn, so that you can safely draw a new line:
private void panel1_MouseMove(object sender, MouseEventArgs e)
{
Pen pen1 = new System.Drawing.Pen(Color.Black, 3);
Pen pen2 = new System.Drawing.Pen(panel1.BackColor, 3);
Graphics g = panel1.CreateGraphics();
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
// Clear the graphics, creating a blank area to draw on
g.Clear(panel1.BackColor);
g.DrawLine(pen1, new Point(0, 0), new Point(e.Location.X, e.Location.Y));
x_previous = e.Location.X;
y_previous = e.Location.Y;
}
Hope this helps!

Instead of drawing the line in the event handler for the mouse movement you should use it to Invalidate the panel and perform the line drawing in a handler for its Paint event. There will be no need to erase the old line.

I haven't used WinForms in a while, so you'll have to forgive me if this doesn't work.
I assume that anti-aliasing has slightly blurred the edges of the line so that the initial line extends slightly further out than the width of the pen. That also means that the edges of the white pen won't be completely opaque when drawing over the black line.
Try increasing the width of the white pen until it completely covers the black, and maybe see if you can leave the Graphics object with lower quality rendering for the white pen, and use the smoothing only for the black pen.

draw multiple curves in WinForms picturebox

I am working on a program which I want to draw diode curves in a WinForms application. I have a list of diode names and I have theire points as you can see at the right side of the picture. That is Voltage as X and Current as Y ( A curve contains like 50 points).
What I want to do is by selecting one or more diodes from the list theire curve show up on my plot. What you see is just a picture box at the moment filled with a bmp. I know that this is not a reliable solution, so I am asking you what can be the best approach to do such thing? I dont know any good component which can make me do this. So I just need to know what can be the best approuch for this task?
A diode curve is something like:
I might have up to 100 of diode curves in my program which all of them (single or multiple) should be drawn by clicking on them in the list.
So what you think?
UPDATE
ALSO important thing is by deselecting a pin in the curve, its curve should be removed from the plot!
I am drawing that axis you see using the code below:
Bitmap xyCords = new Bitmap(500, 500);
Graphics g = Graphics.FromImage(xyCords);
g.DrawLine(penAxis, 250, 0, 250, 500);
g.DrawLine(penAxis, 0, 250, 500, 250);
curveBox.Image = xyCords;
how is it possible later if I made a new Graphics I append it like:
curveBox.Image += newGraphic;
** Please let me know if there is any component or something which already can do what I want. or else show me a good approach! Thanks!

Try using Graphics.DrawCurve. You just put all of the points you want in an array, and pass that and a pen to the method.
Edit:
Add this after your code to prove to yourself that both graphs coexist. To erase one or the other, just plot the same points, but in the background color of the bitmap (test for it, I don't remember what it is).
Point[] ptarray = new Point[3];
ptarray[0] = new Point(250, 250);
ptarray[1] = new Point(300, 300);
ptarray[2] = new Point(350, 400);
Pen pengraph = new Pen(Color.Green, 0.75F);
g.DrawCurve(pengraph, ptarray);
Point[] ptarray2 = new Point[3];
ptarray2[0] = new Point(100, 100);
ptarray2[1] = new Point(200, 150);
ptarray2[2] = new Point(250, 250);
Pen pengraph2 = new Pen(Color.Yellow, 1.25F);
g.DrawCurve(pengraph2, ptarray2);