Double Buffering With GDI+

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Introduction

This is a simple example about GDI+ which I used in my first GDI+ project.This article is focused on Double Buffering. First if you want to add GDI+ supports to your project,you can refer to Starting with GDI+ By Christian Graus.
The main part of my example is in OnPaint function that you can see everything there,Image,Font,Brush and etc.They are very clear so I don't discuss about them.I only explain "Double Buffering" here.


As you know you can draw images into your windows and create a brush or pen from TextureBrush and draw shapes or line, using the image.Even you can draw a text using the images by supplying TextureBrush.(you can see the examples in this article or Christian Grause articles)

I think one of the most important use of images is Double Buffernig technique.This technique is used when the drawing we wish to create has many details,and it is time consuming to draw even with a fast computer.In this situation it seems the image creeps on to the screen while being drawn.For example in mapping applications or CAD/CAM applications we would encounter this problem. In this technique instead of drawing in the screen,first we draw into an image and then we draw the iamge into the window. Here is my example in double buffering:

   srand( (unsigned)time( NULL ) );
   int number = rand();
   number /= RAND_MAX + 1; 
   number *= 254;

   Rect rc(rect.left,rect.top,rect.right,rect.bottom);
      Bitmap bmp(rect.right,rect.bottom);

   // Create a Graphics object that is associated with the image.

   Graphics* graph = Graphics::FromImage(&bmp);
 
   for(int x=0;x<rect.right;x++)
   {
   	for(int y=0; y<rect.bottom; y++)
   	{
   		double number = rand();
  		number /= RAND_MAX + 1; 
		number *= 254;
		Pen pen(Color(number,number,number,number));
		graph->DrawLine(&pen,0,0,x,y);
        	}
	}
   // Draw the altered image.

   graphics.DrawImage(&bmp,rect.left,rect.top,rect.right,rect.bottom);

It takes 36 seconds to paint the screen on my computer(AMD 1.33GHtz and 256Mb RAM) without double buffering but only 5 seconds with this technique.You know,it is not interesting to wait 36 seconds each time that your window need to repaint!

Finally I want to thank Christian Graus for his supports and good articles about GDI+ which I used some of his codes and ideas.