C program to draw parallel lines? - Answers

/* 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); } } }