Introduction to Graphics: Graphics Library, Initialization, and Drawing Primitives

Overview of Computer Graphics in C

Computer graphics in C refers to the ability to draw lines, shapes, and images on the screen using standard library functions. While standard C is text-based, the Borland Graphics Interface (BGI) provides a set of functions to manipulate pixels and create visual outputs.

Why do we need Graphics Functions?

1. Visual Representation: To display data in charts, graphs, or diagrams.
2. User Interface: To create interactive menus, buttons, and windows.
3. Game Development: To render characters, backgrounds, and animations.
4. Simulation: To model physical systems or architectural designs visually.

The Graphics Environment

To use graphics in C, the compiler must support the graphics.h library. The process involves three main phases:

1. Initialization: Setting up the graphics driver and mode.
2. Drawing: Using primitive functions to render shapes.
3. Termination: Closing the graphics mode to return to text mode.

Initialization and Termination

The initgraph() function initializes the graphics system.

int gd = DETECT, gm;
initgraph(&gd, &gm, "C:\\TURBOC3\\BGI");

• gd (Graphics Driver): DETECT automatically selects the best driver.
• gm (Graphics Mode): Specifies the resolution.
• path: The directory where BGI files are located.

After drawing, closegraph() is called to unload the graphics driver and restore the screen.

Drawing Primitives

The following table summarizes common graphics functions:

Worked Examples

Program to Draw a Circle

#include <graphics.h>
#include <conio.h>

int main() {
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "C:\\TURBOC3\\BGI");

    // Draw a circle at center (200, 200) with radius 50
    circle(200, 200, 50);

    getch(); // Wait for user input
    closegraph();
    return 0;
}

Program to Draw Multiple Shapes

#include <graphics.h>
#include <conio.h>

int main() {
    int gd = DETECT, gm;
    initgraph(&gd, &gm, "C:\\TURBOC3\\BGI");

    // Draw a line
    line(50, 50, 200, 50);

    // Draw a rectangle
    rectangle(50, 100, 150, 200);

    getch();
    closegraph();
    return 0;
}

Coordinate System

In the graphics mode, the screen is treated as a grid of pixels.

• The origin (0, 0) is at the top-left corner.
• The x-axis increases from left to right.
• The y-axis increases from top to bottom.

Advantages and Disadvantages

• Advantages: Enhances user experience, simplifies complex data interpretation, and provides a platform for basic game development.
• Disadvantages: Graphics functions are highly dependent on specific compilers (like Turbo C++) and are not part of the standard C library (ANSI C), making them non-portable to modern IDEs like VS Code or GCC.

Exam Tip

• Focus on Syntax: When writing programs in the exam, always include the initgraph and closegraph functions. Forgetting these is a common reason for losing marks.
• Path Specification: If asked for the path in initgraph, use the standard "C:\\TURBOC3\\BGI" as it is the expected answer in TU/PU exams.
• Conceptual Clarity: If asked "Why do we need graphics?", emphasize the transition from text-based interfaces to visual interfaces.
• Diagrams: If asked to draw a shape, clearly label the coordinate parameters (e.g., circle(x, y, r) where x, y is the center).