GDI+ Examples: Circular
 

Introduction

In this example that simulates a screen saver, we draw one circle in the center of the screen. Then we draw four circles around the central one. We use a timer to monitor what is going on. As the timer ticks, the radius of the central circle changes. Also, the radii of the other four circles change. When the radius a circle reaches a maximum, the radius decreases. Then it reaches a minimum, it starts increasing again.

Practical Learning: Starting the Exercise
  1. Start Microsoft Visual C++ .Net and create a new Windows  named Circular
  2. Change the properties of the form as follows:
    BackColor: Black
    FormBorderStyle: None
    WindowState: Maximized
  3. Double-click the middle of the form to generate its Load event
  4. Return to the form and, in the Events section of the Properties window, generate a KeyDown event for it
  5. Return to the form and add a Timer control to it
  6. Set the timer's Enabled to True and its Interval to 20
  7. Double-click the timer and change the file as follows
      
    #pragma once


namespace Circular
{
	using namespace System;
	using namespace System::ComponentModel;
	using namespace System::Collections;
	using namespace System::Windows::Forms;
	using namespace System::Data;
	using namespace System::Drawing;

	/// <summary> 
	/// Summary for Form1
	///
	/// WARNING: If you change the name of this class, you will need to change the 
	///          'Resource File Name' property for the managed resource compiler tool 
	///          associated with all .resx files this class depends on.  Otherwise,
	///          the designers will not be able to interact properly with localized
	///          resources associated with this form.
	/// </summary>
	public __gc class Form1 : public System::Windows::Forms::Form
	{	
	public:
		Form1(void)
		{
			InitializeComponent();
		}
  
	protected:
		void Dispose(Boolean disposing)
		{
			if (disposing && components)
			{
				components->Dispose();
			}
			__super::Dispose(disposing);
		}
	private: System::Windows::Forms::Timer *  timer1;
	private: System::ComponentModel::IContainer *  components;
			 Graphics *graphDrawingArea;
			 Bitmap   *bmpDrawingArea;

	private:
		/// <summary>
		/// Required designer variable.
		/// </summary>


		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		void InitializeComponent(void)
		{
			this->components = new System::ComponentModel::Container();
		this->timer1 = new System::Windows::Forms::Timer(this->components);
			// 
			// timer1
			// 
			this->timer1->Enabled = true;
			this->timer1->Interval = 20;
			this->timer1->Tick += new System::EventHandler(this, timer1_Tick);
			// 
			// Form1
			// 
			this->AutoScaleBaseSize = System::Drawing::Size(5, 13);
			this->BackColor = System::Drawing::Color::Black;
			this->ClientSize = System::Drawing::Size(292, 266);
		this->FormBorderStyle = System::Windows::Forms::FormBorderStyle::None;
			this->MaximizeBox = false;
			this->Name = S"Form1";
			this->Text = S"Form1";
this->KeyDown += new System::Windows::Forms::KeyEventHandler(this, Form1_KeyDown);
			this->Load += new System::EventHandler(this, Form1_Load);

		}	
	private: System::Void Form1_Load(System::Object *  sender, System::EventArgs *  e)
		 {
			 bmpDrawingArea   = new Bitmap(Width, Height);
			graphDrawingArea = Graphics::FromImage(bmpDrawingArea);

			 Cursor::Hide();
		 }

private: System::Void Form1_KeyDown(System::Object *  sender, 
		System::Windows::Forms::KeyEventArgs *  e)
			 {
				 if( e->KeyCode == Keys::Escape )
					 Close();
			 }

			 

	 void DrawCentralCircle(int CenterX, int CenterY, int Radius)
	 {
		 int start = CenterX - Radius;
		 int end   = CenterY - Radius;
		 int diam  = Radius * 2;

		graphDrawingArea->DrawEllipse(new Pen(Color::Blue), start, end, diam, diam);
	 }

	 void DrawCornerCircle(int CenterX, int CenterY, int Radius)
	 {
		 int start = CenterX - Radius;
		 int end   = CenterY - Radius;
		 int diam  = Radius * 2;

		graphDrawingArea->DrawEllipse(new Pen(Color::Red), start, end, diam, diam);
	 }

	private: System::Void timer1_Tick(System::Object *  sender, System::EventArgs *  e)
	 {
		 Graphics *graph = Graphics::FromHwnd(this->Handle);

		 int centerX = ClientRectangle.Width / 2;
		 int centerY = ClientRectangle.Height / 2;

		 static int mainRadius  = 10;
		 static int smallRadius = 5;
		 static bool isMax;
		 static bool smallRadiusMax;

		 if( isMax == true )
			 mainRadius--;
	                 else
			 mainRadius++;

		 if( mainRadius > (ClientRectangle.Height / 2) )
			 isMax = true;
		 if( mainRadius < 10 )
			 isMax = false;

		 if( smallRadiusMax == true )
			 smallRadius--;
                	 else
			 smallRadius++;

		 if( smallRadius > 240 )
			 smallRadiusMax = true;
		 if( smallRadius < 5 )
			 smallRadiusMax = false;

	graphDrawingArea->FillRectangle(new SolidBrush(Color::Black), 0, 0, Width, Height);

		 // Central
		 DrawCentralCircle(centerX, centerY, mainRadius);
		 // Top-Left
		 DrawCornerCircle(centerX/2, centerY/2, smallRadius);
		 // Top-Right
		 DrawCornerCircle(centerX + (centerX/2), centerY/2, smallRadius);
		 // Bottom-Left
		 DrawCornerCircle(centerX/2, centerY + (centerY/2), smallRadius);
		 // BottomRight
		 DrawCornerCircle(centerX + (centerX/2), centerY + (centerY/2), smallRadius);

		 graph->DrawImage(bmpDrawingArea, 0, 0);
	 }

	};
}
  8. Execute the application
 
 
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