from pyx import * unit.set(uscale=3, wscale=3) dist = 0.15 # distance between the ropes thick = 0.08 # thickness of the ropes # build the basepath of the knot. This is the curve that lies # between both ropes. A = 1.0, 0.1 # point where the knot starts after the straight line B = 1.3, 0 # point where the knot is curved, overlying the straight line t = -0.8, -0.1 # direction at A s = 0.3, 1.2 # direction at B pts = [ ( A[0]-t[0], A[1]-t[1]), ( A[0] , A[1] ), ( A[0]+t[0], A[1]+t[1]), (-B[0]-s[0],-B[1]-s[1]), (-B[0] ,-B[1] ), (-B[0]+s[0],-B[1]+s[1]), ( B[0]-s[0], B[1]-s[1]), ( B[0] , B[1] ), ( B[0]+s[0], B[1]+s[1]), (-A[0]-t[0],-A[1]-t[1]), (-A[0] ,-A[1] ), (-A[0]+t[0],-A[1]+t[1]) ] seam = path.path( path.moveto(*(pts[0])), path.lineto(*(pts[1])), path.curveto(pts[2][0],pts[2][1],pts[3][0],pts[3][1],pts[4][0],pts[4][1]), path.curveto(pts[5][0],pts[5][1],pts[6][0],pts[6][1],pts[7][0],pts[7][1]), path.curveto(pts[8][0],pts[8][1],pts[9][0],pts[9][1],pts[10][0],pts[10][1]), path.lineto(*(pts[11])) ) # We smooth this curve a little because we used curveto together with lineto seam = deformer.smoothed(0.6).deform(seam) # The ropes, when drawn later, will have to overlap in a very specific way. l = seam.arclen() epsilon = 0.002*l # small overlap between the segments seam_segs = seam.split([0.28*l+epsilon, 0.28*l-epsilon, 0.42*l+epsilon, 0.42*l-epsilon, 0.58*l+epsilon, 0.58*l-epsilon, 0.72*l+epsilon, 0.72*l-epsilon])[::2] # For each segment, two shifted paths build the boundaries of each rope ropes_segs = [] for seam_seg in seam_segs: ropes_segs.append([]) for ropeshift in [-0.5*dist, 0.5*dist]: ropes_segs[-1].append([]) for edgeshift in [-0.5*thick, 0.5*thick]: ropes_segs[-1][-1].append( deformer.parallel(ropeshift + edgeshift).deform(seam_seg)) # Now, ropes_segs is a list of segments, containing a list of ropes, # each containing the two bounding paths of the rope segment rope_colors = [color.rgb.blue, color.rgb.red] c = canvas.canvas() # Because the segments should overlap in a very specific manner # we have to draw them in the correct order for index in [1, 4, 2, 0, 3]: for rope_seg, col in zip(ropes_segs[index], rope_colors): seg = rope_seg[0].joined(rope_seg[1].reversed()) seg.append(path.closepath()) c.fill(seg, [col]) c.stroke(rope_seg[0], [style.linecap.round, style.linejoin.round]) c.stroke(rope_seg[1], [style.linecap.round, style.linejoin.round]) c.writeEPSfile("knot") c.writePDFfile("knot")