*previous post*), I had fully intended to optimise the trefoil sketch, here is my effort, where some values are pre-calculated, and although it look slightly messy putting values directly into new Vec3D instance:-

# Trefoil, by Andres Colubri # A parametric surface is textured procedurally # by drawing on an offscreen PGraphics surface. # somewhat optimised version for ruby-processing (development version) load_libraries :vecmath, :fastmath attr_reader :pg, :trefoil def setup size(1024, 768, P3D) texture_mode(NORMAL) noStroke # Creating offscreen surface for 3D rendering. @pg = create_graphics(32, 512, P3D) pg.begin_draw pg.background(0, 0) pg.noStroke pg.fill(255, 0, 0, 200) pg.end_draw # Saving trefoil surface into a PShape3D object @trefoil = create_trefoil(350, 60, 15, pg) end def draw background(0) pg.begin_draw pg.ellipse(rand(0.0 .. pg.width), rand(0.0 .. pg.height), 4, 4) pg.end_draw ambient(250, 250, 250) pointLight(255, 255, 255, 0, 0, 200) push_matrix translate(width/2, height/2, -200) rotate_x(frame_count * PI / 500) rotate_y(frame_count * PI / 500) shape(trefoil) pop_matrix end # Code to draw a trefoil knot surface, with normals and texture # coordinates. # Adapted from the parametric equations example by Philip Rideout: # http://iphone-3d-programming.labs.oreilly.com/ch03.html # This function draws a trefoil knot surface as a triangle mesh derived # from its parametric equation. def create_trefoil(s, ny, nx, tex) obj = create_shape() obj.begin_shape(TRIANGLES) obj.texture(tex) (0 ... nx).each do |j| u0 = j.to_f / nx u1 = (j + 1).to_f / nx (0 ... ny).each do |i| v0 = i.to_f / ny v1 = (i + 1).to_f / ny p0 = eval_point(u0, v0) n0 = eval_normal(u0, v0) p1 = eval_point(u0, v1) n1 = eval_normal(u0, v1) p2 = eval_point(u1, v1) n2 = eval_normal(u1, v1) # Triangle p0-p1-p2 n0.shape_normal(obj) pa = p0 * s pa.shape_vertex(obj, u0, v0) n1.shape_normal(obj) pb = p1 * s pb.shape_vertex(obj, u0, v1) n2.shape_normal(obj) pc = p2 * s pc.shape_vertex(obj, u1, v1) p1 = eval_point(u1, v0) n1 = eval_normal(u1, v0) # Triangle p0-p2-p1 n0.shape_normal(obj) pa.shape_vertex(obj, u0, v0) n2.shape_normal(obj) pc.shape_vertex(obj, u1, v1) n1.shape_normal(obj) pb = p1 * s pb.shape_vertex(obj, u1, v0) end end obj.end_shape return obj end # Evaluates the surface normal corresponding to normalized # parameters (u, v) def eval_normal(u, v) # Compute the tangents and their cross product. p = eval_point(u, v) tangU = eval_point(u + 0.01, v) tangV = eval_point(u, v + 0.01) tangU -= p tangV -= p tangV.cross(tangU).normalize! # it is easy to chain Vec3D operations end # Evaluates the surface point corresponding to normalized # parameters (u, v) def eval_point(u, v) a = 0.5 b = 0.3 c = 0.5 d = 0.1 s = TWO_PI * u t = (TWO_PI * (1 - v)) * 2 sint = FastMath.sin(t) cost = FastMath.cos(t) sint15 = FastMath.sin(1.5 * t) cost15 = FastMath.cos(1.5 * t) r = a + b * cost15 x = r * cost y = r * sint z = c * sint15 dv = Vec3D.new( -1.5 * b * sint15 * cost - y, -1.5 * b * sint15 * sint + x, 1.5 * c * cost15) q = dv.normalize # regular normalize creates a new Vec3D for us qvn = Vec3D.new(q.y, -q.x, 0).normalize! # chained Vec3D operations ww = q.cross(qvn) coss = FastMath.cos(s) sins = FastMath.sin(s) Vec3D.new( x + d * (qvn.x * coss + ww.x * sins), y + d * (qvn.y * coss + ww.y * sins), z + d * ww.z * sins) end

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