drawLineXY.m

function [indexes pic] = drawLineXY(picture, x1, y1, x2, y2, color)
	if ~ exist('color','var') || isempty(color)
		display "Color undefined, then I'll pick 'black':";
		color = 0;
	end
	% distances according to both axes
	xn = abs(x2-x1);
	yn = abs(y2-y1);

	% interpolate against axis with greater distance between points;
	% this guarantees statement in the under the first point!
	if (xn > yn)
		xc = x1 : sign(x2-x1) : x2;
		yc = round( interp1([x1 x2], [y1 y2], xc, 'linear') );
	else
		yc = y1 : sign(y2-y1) : y2;
		xc = round( interp1([y1 y2], [x1 x2], yc, 'linear') );
	end

	% 2-D indexes of line are saved in (xc, yc), and
	% 1-D indexes are calculated here:
	indexes = sub2ind( size(picture), yc, xc );
	
	% draw line on the image (change value of '255' to one that you need)
	picture(indexes) = color;
	pic = picture;
	imshow(picture);