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--PICTURE scene: Ellipse update-demo (anim)

--Demonstrates 'interactive' features.

--by Richard Fhager

-- Copyright 2011 Richard Fhager

--

-- This program is free software; you can redistribute it and/or

-- modify it under the terms of the GNU General Public License

-- as published by the Free Software Foundation; version 2

-- of the License. See 

--

-- rot: Rotation in degrees

-- stp: Step is # of line segments (more is "better")

-- a & b are axis-radius

function ellipse2(x,y,a,b,stp,rot,col)

 local n,m=math,rad,al,sa,ca,sb,cb,ox,oy,x1,y1,ast

 m = math; rad = m.pi/180; ast = rad * 360/stp;

 sb = m.sin(-rot * rad); cb = m.cos(-rot * rad)

 for n = 0, stp, 1 do

  ox = x1; oy = y1;

  sa = m.sin(ast*n) * b; ca = m.cos(ast*n) * a

  x1 = x + ca * cb - sa * sb

  y1 = y + ca * sb + sa * cb

  if (n > 0) then drawline(ox,oy,x1,y1,col); end

 end

end

--

setpicturesize(300,300)

setcolor(0,96,96,96)

setcolor(1,255,255,128)

r1 = 100

r2 = 50

rt = 0

frames = 100

while (1 < 2) do

 r1t = 10 + math.random() * 140

 r2t = 10 + math.random() * 140

 rtt = math.random() * 360

for n = 0, frames-1, 1 do

 clearpicture(0)

 f2 = n / frames

 f1 = 1 - f2

 r1a = r1*f1 + r1t*f2

 r2a = r2*f1 + r2t*f2

 rta = rt*f1 + rtt*f2

 --       x,   y,   r1,  r2,  stp, rot, col

 ellipse2(150, 150, r1a, r2a, 50,  rta, 1)

  statusmessage('press ESC to stop')

  updatescreen();if (waitbreak(0)==1) then return end

end

 r1,r2,rt = r1a,r2a,rta

end