C program to draw parallel lines?

Answer 1

/* This is an incomplete program. The function below will draw two parallel lines, but depends on a putpixel function that is not defined here. Also of course needs a main function calling it somewhere, and all the other usual necessities. */

/* draw a line from point (x1, y1) to point (x2, y2) and another one that is (xoffset, yoffset) pixels away from it. Uses Bresenham's line algorithm and depends on a "putpixel" function */

void pline(int x1, int y1, int x2, int y2, int xoffset, yoffset){

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);

putpixel(drawx + xoffset, drawy + yoffset);

if(deltaxabs >= deltayabs){

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

y += deltayabs;

if(y >= deltaxabs){

y -= deltaxabs;

drawy += sgndeltay;

}

drawx += sgndeltax;

putpixel(drawx, drawy);

putpixel(drawx + xoffset, drawy + yoffset);

}

}else{

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

x += deltaxabs;

if(x >= deltayabs){

x -= deltayabs;

drawx += sgndeltax;

}

drawy += sgndeltay;

putpixel(drawx, drawy);

putpixel(drawx + xoffset, drawy + yoffset);

}

}

}