Just another update

Task/Bitmap-Bresenhams-line-algorithm/Prolog/bitmap-bresenhams-line-algorithm.pro

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+use_module(library(pce)).
+lindraw(X1,Y1,X2,Y2):-
+	new(Win,window("Line")),
+	new(Pix,pixmap(@nil,black,white,X2+30,Y2+30)),
+	send(Win,size,size(400,400)),
+	draw_line(Pix,X1,Y1,X2,Y2),
+	new(Bmp,bitmap(Pix)),
+	send(Win,display,Bmp,point(0,0)),
+	send(Win,open).
+
+draw_recursive_line(_Pict,X,X,_DX,_DY,Y,Y,_D,_Sx,_Sy).%Don't iterate if X and X2 are the same number
+draw_recursive_line(Pict,X,X2,DX,DY,Y,Y2,C,Sx,Sy):-
+	(   C>0->%If the difference is greater than one, add Y one to Y.
+	Y1 is Y+Sy,
+	    send(Pict,pixel(X,Y1,colour(black))),
+	    C2 is C+(2*DY-2*DX);
+	Y1 is Y,
+	send(Pict,pixel(X,Y,colour(black))),
+	    C2 is C+(2*DY)),
+	X0 is X+Sx,%The next iteration
+	draw_recursive_line(Pict,X0,X2,DX,DY,Y1,Y2,C2,Sx,Sy).
+isneg(X,O):-
+	(   X<0->
+
+	O is -1;
+	(   X\==0->
+	O is 1;
+	O is 0)).
+
+draw_line(Pict,X1,Y1,X2,Y2):-
+	DY is abs(Y2-Y1),
+	DX is abs(X2-X1),
+	isneg(DX,Sx),
+	isneg(DY,Sy),
+	D = 2*DY-DX,%The slope of the line
+	draw_recursive_line(Pict,X1,X2,DX,DY,Y1,Y2,D,Sx,Sy).