Clarification on skeleton code for C graphics library

Question

I'm studying C and I've been given this code which draws a single line of pixels:

void draw_line(unsigned char x1, unsigned char y1, unsigned char x2, unsigned char y2) {
// Insert algorithm here.
if (x1 == x2) {
    //Draw Horizontal line
    unsigned char i;
    for (i = y1; i <= y2; i++){
        set_pixel(x1, i, 1);
    }           
} else if (y1 == y2){
    //Draw vertical line
    unsigned char i;
    for (i = x1; i <= x2; i++){
        set_pixel(i, y1, 1);
    }       

I understand how it works, but not how to implement it. Could someone provide an example of how to use it?

Answer 1

Hope This will help you:

Algorithm:
1)Get the X and Y co-ordinates of the start and end points of the line.
2)Find the difference in the X and Y co-ordinates values as dx and dy.
3)Check if dx is greater of dy is greater and assign the greater value to 'steps'.
4)Increment X and Y values at regular intervals by dividing the corresponding axes difference by steps.
5)Plot the initial point by using “PUTPIXEL” syntax.
6)Repeat step 4 'steps' number of times and mark the end point by using “PUTPIXEL” syntax.
7)End the program.

Program:
#include"graphics.h"

#include"stdio.h"

#include"conio.h"

#include"math.h"

void linedraw(int,int,int,int);

int main()

{

    int x1coeff,y1coeff,x2coeff,y2coeff;

    printf("\Enter the x and y value for starting point:");

    scanf("%d%d",&x1coeff,&y1coeff);

    printf("\Enter the x and y value for end point:");

    scanf("%d%d",&x2coeff,&y2coeff);

    linedraw(x1coeff,y1coeff,x2coeff,y2coeff);

    getch();

    return 0;


}

void linedraw(int xa,int ya,int xb,int yb)

{

    int dx,dy,steps,k;

    int gdriver=DETECT,gmode;

    float xinc,yinc,x,y;

    initgraph(&gdriver,&gmode,""); //initialise graphics

    dx=xb-xa;

    dy=yb-ya;

    x=xa;

    y=ya;

    if(abs(dx)>abs(dy))

    {

        steps=abs(dx);

    }

    else

    {

        steps=abs(dy);

    }

    xinc=dx/steps;

    yinc=dy/steps;

    putpixel(x,y,WHITE);

    for(k=0;k
    {

        x+=xinc;

        y+=yinc;

        putpixel(x,y,WHITE);

    }}


Output:

 Enter the x and y value for starting point:100 100

 Enter the x and y value for end point:200 200

 The Line drawn is