Theory about applications - [TA5]

Introduction

The Graphics class encapsulates GDI+ drawing surfaces. Before drawing any object (for example circle, or rectangle) we have to create a surface using Graphics class. Generally we use Paint event of a Form to get the reference of the graphics. Another way is to override OnPaint method. Here is how you get a reference of the Graphics object:

private void form1_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;
}
//OR
protected override void OnPaint(PaintEventArgs e)
{
    Graphics g = e.Graphics;
}

Once you have the Graphics reference, you can call any of this class’s members to draw various objects. Here are some of Graphics class’s methods:

Graphics Objects

After creating a Graphics object, you can use it draw lines, fill shapes, draw text and so on. The major objects are:

The Pen Class

A pen draws a line of specified width and style. You always use Pen constructor to create a pen. The constructor initializes a new instance of the Pen class. You can initialize it with a color or brush.
Initializes a new instance of the Pen class with the specified Color and Width.

public Pen(Color, float);
//Here is one example:
Pen pn = new Pen( Color.Blue, 100 );

The Brush Class

The Brush class is an abstract base class and cannot be instantiated. We always use its derived classes to instantiate a brush object, such as SolidBrush, TextureBrush, RectangleGradientBrush, and LinearGradientBrush.
Here is one example:

Brush brsh = new SolidBrush(Color.Red), 40, 40, 140, 140);

The SolidBrush class defines a brush made up of a single color. Brushes are used to fill graphics shapes such as rectangles, ellipses, pies, polygons, and paths.
The TextureBrush encapsulates a Brush that uses an fills the interior of a shape with an image.
The LinearGradiantBrush encapsulates both two-color gradients and custom multi-color gradients.

The Rectangle Object

Its constructor initializes a new instance of the Rectangle class. Here is the definition:

public Rectangle(Point, Size);
//OR
public Rectangle(int, int, int, int);

The Rectangle Object is used to draw a rectangle on WinForms. Besides its constructor, the Rectangle Object has following members:

Example: Drawing a rectangle

We can override OnPaint event of your form to draw an rectangle. The LinearGradientBrush encapsulates a brush and linear gradient.

protected override void OnPaint(PaintEventArgs pe)
{
    Graphics g = pe.Graphics ;
    Rectangle rect = new Rectangle(50, 30, 100, 100);
    LinearGradientBrush lBrush = new LinearGradientBrush(
                                    rect,
                                    Color.Red,
                                    Color.Yellow,
                                    LinearGradientMode.BackwardDiagonal
                                );
    g.FillRectangle(lBrush, rect);
}

A useful application of the rectangle object can be its use as a “canvas” for a bitmap object. Doing so will allow to control the size of the chart and its scale by interacting with the rectangle object and in particular it can be used to plot charts within its area.

Example: Creating a bitmap

Let’s now see how to create a simple bitmap that we can then use as described above, and as it can be seen in the applications developed.

Bitmap image = new Bitmap(width, height);
// We can also assign the bitmap to a picturebox to draw on it
pictureBox.Image = image;

Sources

• https://learn.microsoft.com/en-us/dotnet/desktop/winforms/advanced/graphics-and-drawing-in-windows-forms?view=netframeworkdesktop-4.8
• https://learn.microsoft.com/en-us/dotnet/api/system.drawing.graphics?view=windowsdesktop-7.0