[Last Call] Learn how to a build a cloud-first strategyRegister Now

x
?
Solved

How to delete rectangle drew with GDI

Posted on 2004-08-17
4
Medium Priority
?
1,707 Views
Last Modified: 2007-12-19
Hi,
I have simple question regarding to drawing with GDI.
How can I delete things which I drew with GDI, I mean for instance, a rectangle.
I’m using following code to draw rectangle:

                        Graphics gfx = this.tabControlPanel3.CreateGraphics();
                  Rectangle rc = new Rectangle(10,20,100,200);
                  gfx.SmoothingMode = SmoothingMode.AntiAlias;
                  Pen pen = new Pen(Brushes.Red,3);
                  gfx.DrawRectangle(pen,rc);

I want to delete this rectangle from my Form after pressing a button.

Thanks for your help.
0
Comment
Question by:knobloch
  • 3
4 Comments
 
LVL 3

Expert Comment

by:bigjim2000
ID: 11839281
Well, the short answer is, you can't :-p

You must redraw the form without drawing the rectangle.... either that, or draw a new rectangle (over the old one) that is the same color as the background, as to hide it.

There is no "undo" with GDI.

You can liken your gdi surface to painting with a permanent pen.  The only thing you can do is to paint over it with another pen :-p (I know, bad example, but I'm trying!)

-Eric
0
 
LVL 3

Expert Comment

by:bigjim2000
ID: 11839480
Here is a simple example.  I created 2 buttons, one for draw, the other for, erhm, undraw.

Here's the code:

private void btnDraw_Click(object sender, System.EventArgs e)
{
      System.Drawing.Graphics gfx = this.CreateGraphics();
      System.Drawing.Brush b = new System.Drawing.SolidBrush(System.Drawing.Color.Red);
      System.Drawing.Pen p = new System.Drawing.Pen(b, 3.0f);
      gfx.DrawRectangle(p, btnDraw.Left - 10, btnDraw.Top - 10, btnDraw.Width + 20, btnDraw.Height + 20);
}

private void button2_Click(object sender, System.EventArgs e)
{
      System.Drawing.Graphics gfx = this.CreateGraphics();
      System.Drawing.Brush b = new System.Drawing.SolidBrush(this.BackColor);
      System.Drawing.Pen p = new System.Drawing.Pen(b, 3.0f);
      gfx.DrawRectangle(p, btnDraw.Left - 10, btnDraw.Top - 10, btnDraw.Width + 20, btnDraw.Height + 20);
}

Should be a start for you.

-Eric
0
 

Author Comment

by:knobloch
ID: 11842555
I can't use color of my Form as a color for brush because my form has gradient background and brush this.BacColor will mess up my background.
Anyway thanks, maybe I will repaint my form, but it seems not good idea if you have to do this many times. I will test it.
0
 
LVL 3

Accepted Solution

by:
bigjim2000 earned 2000 total points
ID: 11844021
Well, if you just do it when you click a button, that is nothing, go ahead and repaint your form using similar code as above.  If you are going to be drawing it several times per second, then I would suggest implementing a double buffered system.  This has 2 graphics surfaces.  You draw to one of them, then when you are finished drawing, you copy over the entire thing.  This eliminates (mostly) the flickering you see when you draw a lot at once on the screen.

Another thing to consider, is to paint your form once to a bitmap in memory (your gradient background).  Then when you want to draw your form, you copy the bitmap in memory.  Then you draw on the form a bit, then you can copy the gradient bitmap again, only this time, just copy part of it (where you drew on the form).

-Eric
0

Featured Post

Concerto Cloud for Software Providers & ISVs

Can Concerto Cloud Services help you focus on evolving your application offerings, while delivering the best cloud experience to your customers? From DevOps to revenue models and customer support, the answer is yes!

Learn how Concerto can help you.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction This article series is supposed to shed some light on the use of IDisposable and objects that inherit from it. In essence, a more apt title for this article would be: using (IDisposable) {}. I’m just not sure how many people would ge…
It was really hard time for me to get the understanding of Delegates in C#. I went through many websites and articles but I found them very clumsy. After going through those sites, I noted down the points in a easy way so here I am sharing that unde…
In a question here at Experts Exchange (https://www.experts-exchange.com/questions/29062564/Adobe-acrobat-reader-DC.html), a member asked how to create a signature in Adobe Acrobat Reader DC (the free Reader product, not the paid, full Acrobat produ…
Whether it be Exchange Server Crash Issues, Dirty Shutdown Errors or Failed to mount error, Stellar Phoenix Mailbox Exchange Recovery has always got your back. With the help of its easy to understand user interface and 3 simple steps recovery proced…
Suggested Courses
Course of the Month18 days, 6 hours left to enroll

830 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question