如何平滑地画出贝塞尔曲线 - Project1

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class Bezier
attr_accessor :p1, :p2, :p3, :p4
def initialize(p1,p2,p3,p4)#p1,p4为端点，p2,p3为控制点
@p1 = p1 ; @p2 = p2 ; @p3 = p3 ; @p4 = p4
end
def show_bezier_sprite(viewport, width = 1, color = Color.new(255, 255, 255))#返回一个精灵显示曲线。
rx = [p1.x,p2.x,p3.x,p4.x].min
ry = [p1.y,p2.y,p3.y,p4.y].min
rw = [p1.x,p2.x,p3.x,p4.x].max
rh = [p1.y,p2.y,p3.y,p4.y].max
rh -= ry ; rw -= rx
w = width/2.0 + 3
rx -= w ; ry -= w ; rh += 2*w ; rw += 2*w
rx = rx.to_i ; ry = ry.to_i ; rh = rh.to_i ; rw = rw.to_i
#整个图形必定限制在矩形rx,ry,rw,rh中
sprite = Sprite.new(viewport)
sprite.bitmap = Bitmap.new(rw, rh)
sprite.x = rx ; sprite.y = ry
cp1 = @p1 - Point.new(rx, ry)
cp2 = @p2 - Point.new(rx, ry)
cp3 = @p3 - Point.new(rx, ry)
cp4 = @p4 - Point.new(rx, ry)
#p为以窗口左上角为0点的点，cp为以bitmap左上角为原点的点
coefficien_a = cp4-cp3*3+cp2*3-cp1
coefficien_b = cp3*3-cp2*6+cp1*3
coefficien_c = cp2*3-cp1*3
coefficien_d = cp1
lastp = cp1.to_i
sprite.bitmap.set_pixel(lastp.x, lastp.y, color)
for n in 1..100#这个数据可更改，数据越大，精度越高。若更改，下面的100.0也要改。
t = n/100.0
thisp = (coefficien_a*t**3+coefficien_b*t**2+coefficien_c*t+coefficien_d).to_i
if thisp.distance_to(lastp) > 1.42 then
sprite.bitmap.simple_draw_line(lastp.x, lastp.y, thisp.x, thisp.y, color)
else
sprite.bitmap.set_pixel(thisp.x, thisp.y, color)
end
lastp = thisp
end
return sprite
end
end

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viewport = Viewport.new(0, 0, 544, 416)
p1 = Point.new(50, 50)
p2 = Point.new(50, 400)
p3 = Point.new(500, 400)
p4 = Point.new(500, 50)
bezier = Bezier.new(p1, p2, p3, p4)
sb = bezier.show_bezier_sprite(viewport, 1, Color.new(0, 255, 0))

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