GDI+: Line-Based Shapes

Regular Shapes   Rectangles and Squares A rectangle is a geometric figure made of four sides that compose four right angles. To draw a rectangle, you can either specify the Rectangle value that encloses it, or you can define its location and its dimensions. To draw a rectangle that is enclosed in a Rectangle value, you can use the following version of the Graphics::DrawRectangle() method: public: void DrawRectangle(Pen *pen, Rectangle rect); Remember that such a rectangle object can be illustrated as follows: After defining a Rectangle variable, you can pass it to the method. Here is an example: private: System::Void Form1_Paint(System::Object * sender, System::Windows::Forms::PaintEventArgs * e) { Pen *penCurrent = new Pen(Color::Red); Rectangle Rect(20, 20, 248, 162); e->Graphics->DrawRectangle(penCurrent, Rect); } Remember that you can also define a Pen and/or a Rectangle objects in the parentheses of the method: private: System::Void Form1_Paint(System::Object * sender, System::Windows::Forms::PaintEventArgs * e) { e->Graphics->DrawRectangle(new Pen(Color::Red), Rectangle(20, 20, 248, 162)); } This would produce: It is (very) important to remember that the third argument of the Rectangle represents its width (and not its right) value and the fourth argument represents its height (and not its bottom) value. This is a confusing fact for those who have programmed in GDI: GDI+ defines a Rectangle differently than GDI. In fact, to determine the location and dimensions of a rectangle to draw, the Graphics class provides the following versions of the DrawRectangle() method: public: void DrawRectangle(Pen *pen, int x, int y, int width, int height); public: void DrawRectangle(Pen *pen, float x, float y, float width, float height); This time, the rectangle is represented by its location with a point at (x, y) and its dimensions with the width and height argument. This can be illustrated in a Windows coordinate system as follows: Based on this, the earlier rectangle can also be drawn with the following: private: System::Void Form1_Paint(System::Object * sender, System::Windows::Forms::PaintEventArgs * e) { e->Graphics->DrawRectangle(new Pen(Color::Red), 20, 20, 248, 162); } A square is a rectangle whose four sides are equal.

public: void DrawRectangles(Pen *pen, Rectangle rects[]);
public: void DrawRectangles(Pen *pen, RectangleF rects[]);

private: System::Void Form1_Paint(System::Object *  sender, System::Windows::Forms::PaintEventArgs *  e)
{
	 Pen *penCurrent = new Pen(Color::Red);
	 Rectangle Rect[] = { Rectangle(20,  20, 120, 20),
		                  Rectangle(20,  50, 120, 30),
			  Rectangle(20,  90, 120, 40),
			  Rectangle(20, 140, 120, 60) };

	 e->Graphics->DrawRectangles(penCurrent, Rect);
}

This would produce:

 

Lines

 

A Line

A line is a junction of two points. This means that a line has a beginning and an end: The beginning and the end are two distinct points. Based on this, a line is represented either with two Point values or by four numbers representing its values on the Cartesian axes. To draw a line, the Graphics class is equipped with the following overloaded DrawLine() method:  public: void DrawLine(Pen *pen, Point pt1, Point pt2); public: void DrawLine(Pen *pen, PointF pt1, PointF pt2); public: void DrawLine(Pen *pen, int x1, int y1, int x2, int y2); public: void DrawLine(Pen *pen, float x1, float y1, float x2, float y2); If the line is represented with natural numbers, its origin can be specified as a Point pt1 and its end would be represented with a Point pt2. If the line is drawn using floating numbers, you can start it at one PointF pt1 and end it at another PointF pt2. Otherwise, you can specify the starting point with coordinates (x1, y1) and the end would be represented with coordinates (x2, y2). The same type of line can be drawn using decimal values from coordinates (x1, y1) to coordinates (x2, y2). Here is an example that draws three lines:

private: System::Void Form1_Paint(System::Object * sender, System::Windows::Forms::PaintEventArgs * e) { Pen *penCurrent = new Pen(Color::Red); e->Graphics->DrawLine(penCurrent, 20, 20, 205, 20); penCurrent = new Pen(Color::Green); e->Graphics->DrawLine(penCurrent, 40, 40, 225, 40); penCurrent = new Pen(Color::Blue); e->Graphics->DrawLine(penCurrent, 30, 60, 215, 60); }

 

A Series of Lines

The above DrawLine() method is used to draw one line. If you intend to draw a group of lines at once, you can use the Graphics::DrawLines() method. It is overloaded with two versions as follows: public: void DrawLines(Pen *pen, Point points[]); public: void DrawLines(Pen *pen, PointF points[]); To use this method, you should first define an array of either Point for natural numbers that represent Cartesian coordinates or PointF for floating numbers. Here is an example:

private: System::Void Form1_Paint(System::Object *  sender, System::Windows::Forms::PaintEventArgs *  e)
{
	 Point Coordinates[] = { Point(20, 10), Point(205, 20),
                                                       Point(40, 40), Point(225, 60),
                                                       Point(30, 80), Point(215, 100) };
						
	 Pen *penCurrent = new Pen(Color::Red);
	 e->Graphics->DrawLines(penCurrent, Coordinates);
}

This would produce:

public: void DrawPolygon(Pen *pen, Point points[]);
public: void DrawPolygon(Pen *pen, PointF points[]);

private: System::Void Form1_Paint(System::Object *  sender, System::Windows::Forms::PaintEventArgs *  e)
{
	 Point Pt[] = { Point(20, 50), Point(180, 50), Point(180, 20),
                                       Point(230, 70), Point(180, 120), Point(180, 90),
      	                       Point(20,  90) };

	 Pen *penCurrent = new Pen(Color::Red);
	 e->Graphics->DrawPolygon(penCurrent, Pt);
}

This would produce: