Graphics.DrawLine Method Overview

Overview

This lecture explains the Graphics.DrawLine method from the System.Drawing namespace in .NET, covering its purpose, overloads, parameters, usage, and exceptions.

Purpose and Definition

The Graphics.DrawLine method draws a line connecting two specified points.
It is used in GDI+ drawing for Windows Forms and other .NET graphics contexts.

Method Overloads

There are four main overloads of DrawLine:
- DrawLine(Pen, int x1, int y1, int x2, int y2) draws a line between two integer coordinate pairs.
- DrawLine(Pen, float x1, float y1, float x2, float y2) draws a line between two floating-point coordinate pairs.
- DrawLine(Pen, Point pt1, Point pt2) draws a line between two Point structures (integer values).
- DrawLine(Pen, PointF pt1, PointF pt2) draws a line between two PointF structures (floating-point values).

Parameters and Exceptions

All overloads require a Pen object, which sets the line's color, width, and style.
The start and end points are given as either numeric coordinates or point structures.
An ArgumentNullException is thrown if the pen parameter is null.

Example Usage

Example code creates a black pen and draws a horizontal line using the provided coordinates or points.
These examples are designed for use within a Windows Forms Paint event handler, using PaintEventArgs e.

Platform and Version Support

Supported in .NET (versions 8, 9, 10 and above), .NET Framework (1.1 to 4.8.1), .NET Standard (2.0+), and Windows Desktop (3.0 to 10.0).

Key Terms & Definitions

Pen — Object specifying the line’s color, width, and style.
Point / PointF — Structures representing 2D coordinates using integers (Point) or floats (PointF).
ArgumentNullException — Exception thrown when a required argument is null.
GDI+ — Microsoft’s graphics device interface used in Windows Forms rendering.

Action Items / Next Steps

Review the Using a Pen to Draw Lines and Shapes documentation for more drawing techniques.
Practice implementing DrawLine in a sample Windows Forms project.