Code in c to draw line?

Answer 1

// macros for simplicity

#define MAX(x,y) (x>y?x:y)

#define MIN(x,y) (x<y?x:y)

/*

** drawLine

**

** Draw a line from vertex (x0,y0) to vertex (x1,y1) using

** the midpoint line algorithm, implemented using OpenGL.

**

*/

void drawLine( GLint x0, GLint y0, GLint x1, GLint y1 ) {GLint dE, dNE, x, y, d, dx, dy;

// check if we need to switch the points

if( x0 > x1 ) {

x0 = x0 + x1;

x1 = x0 - x1;

x0 = x0 - x1;

y0 = y0 + y1;

y1 = y0 - y1;

y0 = y0 - y1;}

// calculate deltas

dy = y1 - y0; dx = x1 - x0;

// special cases

if( dx -1 - diag down-right

glBegin(GL_POINTS);

for( x = x0, y = y0; x <= x1; x++, y-- ) {

glVertex2i(x,y);}

glEnd();}else { // general cases

// midpoint algorithm

if( abs(dy) < dx ) { // small slope

dE = 2 * abs(dy);

dNE = 2 * (abs(dy) - dx);

d = dE - dx;

glBegin(GL_POINTS);

for( x = x0, y = y0; x <= x1; x++ ) {

glVertex2i(x,y);

if( d <= 0 ) {

d+= dE;}else {

y += (dy>0?1:-1);

d += dNE;}}// for x = x0 to x1

glEnd();}else { // large slope

dE = 2 * dx;

dNE = 2 * (dx - abs(dy));

d = dE - abs(dy);

glBegin(GL_POINTS);

for( x = x0, y = y0; (y0 < y1 && y <= y1)

(y0 > y1 && y >= y1); y+=(y0 < y1?1:-1) ) {

glVertex2i(x,y);

if( d <= 0) { x ++;

d+= dE; }else { d += dNE; }}// for y = y0 to y1

glEnd();}}

}// drawLine()

Answer 2

The best known method for drawing a line is with Bresenham's line algorithm. An example of it in C is as follows, with the helper functions "sgn", which returns the sign of an integer, and "putpixel", which draws a pixel at the specified location:

void line(int x1, int y1, int x2, int y2){

int n, deltax, deltay, sgndeltax, sgndeltay, deltaxabs, deltayabs, x, y, drawx, drawy;

deltax = x2 - x1;

deltay = y2 - y1;

deltaxabs = abs(deltax);

deltayabs = abs(deltay);

sgndeltax = sgn(deltax);

sgndeltay = sgn(deltay);

x = deltayabs >> 1;

y = deltaxabs >> 1;

drawx = x1;

drawy = y1;

putpixel(drawx, drawy);

if(deltaxabs >= deltayabs){

for(n = 0; n < deltaxabs; n++){

y += deltayabs;

if(y >= deltaxabs){

y -= deltaxabs;

drawy += sgndeltay;

}

drawx += sgndeltax;

putpixel(drawx, drawy);

}

}else{

for(n = 0; n < deltayabs; n++){

x += deltaxabs;

if(x >= deltayabs){

x -= deltayabs;

drawx += sgndeltax;

}

drawy += sgndeltay;

putpixel(drawx, drawy);

}

}

}