Graphics Functions in C: initgraph, line, circle, arc, ellipse, setcolor | Unit 3 | BKNMU BCA
BKNMU Junagadh | BCA Sem 1 | Unit 3
Graphics Functions in C: Complete Guide to 2D Primitives & Controls
Comprehensive breakdown of initgraph, closegraph, line, circle, arc, ellipse, getx, outtextxy, setcolor, and setbkcolor
graphics.h library switches the screen into pixel-addressable graphics mode, allowing you to draw geometric shapes, manage color palettes, and handle graphical coordinates. This comprehensive guide covers all essential graphics functions tailored specifically for BKNMU BCA Semester 1 (Unit 3).
The graphics system in C organizes visual routines into four primary categories:
1. System Control
Initializes the Borland Graphics Interface (BGI) subsystem, switches to graphics mode, and restores standard console mode on completion.
2. Geometric Shapes
Draws fundamental 2D shapes on screen using coordinate-based mathematical plotting for lines, circles, arcs, and ellipses.
3. Color Attributes
Controls drawing and background colors using predefined constants or numeric values (0–15) to style shapes and viewports.
4. Cursor & Text
Retrieves the current graphical pen positions (X, Y) and outputs formatted text directly at exact pixel coordinates.
A detailed reference of function prototypes, parameters, and behaviors for your exam preparation:
| Function Prototype | Functional Purpose | Parameters / Return Type |
|---|---|---|
void initgraph(int*, int*, char*) |
Initializes the graphics hardware driver and switches the monitor into graphics mode. | Takes Driver address, Mode address, and BGI directory string path. |
void closegraph(void) |
Deallocates all graphics system memory and restores the screen to standard text mode. | Takes no parameters. Returns nothing (void). |
void line(int, int, int, int) |
Draws a straight line segment between two specified coordinate points on the screen. | Coordinates: (x1, y1, x2, y2). |
void circle(int, int, int) |
Draws a circle with a given center point and radius using the current drawing color. | Center coordinate (x, y) and radius integer r. |
void arc(int, int, int, int, int) |
Draws a circular arc from a start angle to an end angle along a given radius. | Center (x, y), Start Angle, End Angle, and Radius. |
void ellipse(int, int, int, int, int, int) |
Draws an elliptical arc or complete ellipse using horizontal and vertical radii. | Center (x, y), Start/End angles, X-radius, and Y-radius. |
int getx(void) |
Returns the current X-coordinate position of the graphical drawing cursor. | Takes no parameters. Returns integer X-coordinate. |
int gety(void) |
Returns the current Y-coordinate position of the graphical drawing cursor. | Takes no parameters. Returns integer Y-coordinate. |
void setcolor(int) |
Sets the current drawing color for all subsequent line, circle, and shape operations. | Color code integer (0–15) or constants like WHITE, RED. |
void setbkcolor(int) |
Sets the background color of the active graphics display screen window. | Color code integer (0–15) or standard color constants. |
- The origin coordinate
(0, 0)is located at the top-left corner of the screen. - The X-axis values increase horizontally from left to right.
- The Y-axis values increase vertically from top to bottom.
- Angles in
arc()andellipse()are measured in degrees counter-clockwise, where 0° is at 3 o'clock.
The following program demonstrates initialization, drawing shapes, setting colors, and proper system closure:
#include <stdio.h>
#include <conio.h>
#include <graphics.h> // Required for all graphics functions
int main() {
// 1. Request auto-detection of graphics driver
int gd = DETECT, gm;
// 2. Initialize graphics mode (specify BGI folder path in Turbo C)
initgraph(&gd, &gm, "C:\\Turboc3\\BGI");
// 3. Set Background & Drawing Colors
setbkcolor(BLACK);
setcolor(WHITE);
// 4. Draw a Straight Line: from (50, 50) to (250, 50)
line(50, 50, 250, 50);
// 5. Draw a Circle: Center (150, 150), Radius 50
setcolor(YELLOW);
circle(150, 150, 50);
// 6. Draw an Arc: Center (350, 150), Angles 0 to 180, Radius 50
setcolor(GREEN);
arc(350, 150, 0, 180, 50);
// 7. Draw an Ellipse: Center (250, 300), Angles 0 to 360, X-rad 80, Y-rad 40
setcolor(CYAN);
ellipse(250, 300, 0, 360, 80, 40);
// 8. Display Current Cursor Position
outtextxy(50, 380, "Graphics Primitives Demonstration Successful!");
// 9. Pause execution to view drawing
getch();
// 10. Close graphics mode and restore text console
closegraph();
return 0;
}Step 1: Driver Detection & Mode Switch
Calling initgraph() loads the hardware display driver (e.g., EGAVGA.BGI), configures screen resolution, and allocates video display memory.
Step 2: Attribute Setup & Primitive Rendering
Drawing routines render pixels onto the display buffer based on color parameters and the top-left oriented Cartesian pixel matrix.
Step 3: Cleanup & Memory Deallocation
Calling closegraph() resets the video display controller back to standard alphanumeric character mode and frees system RAM.
initgraph(). Providing an invalid BGI path (such as "" when the files are in C:\Turboc3\BGI) causes a runtime initialization failure.
closegraph() leaves the video controller in high-resolution graphics mode. When the program terminates, the standard text terminal may become unresponsive or display garbled characters. Always pair initgraph() with closegraph().
- Header:
#include <graphics.h> - initgraph(&gd, &gm, path): Loads BGI driver and initializes graphics mode.
- closegraph(): Shuts down the graphics system and frees memory.
- line(x1, y1, x2, y2): Plots a straight line between two points.
- circle(x, y, r): Draws a circle around center
(x, y)with radiusr. - arc(x, y, st, end, r): Draws an angular arc segment.
- ellipse(x, y, st, end, xrad, yrad): Draws elliptical curves or full ellipses.
- setcolor() / setbkcolor(): Controls foreground drawing and screen background colors.