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107.bas

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''' Bezier_pen

'' with Pen/Mouse

'' for SmallBasic-v0.9.0.3

'' on Win98se, by Ted Clayton

'' references:

'' "Learning Mathematics with Micros"

'' by A. Oldknow & D. Smith, p.81

'' Sketch.sb, for Pen/Mouse code

? "Pick a line by left-clicking"

? "two points on the screen."

? "Then, pick a 3rd point, to"

? "the side of the line. The"

? "line will rubber-band toward,"

? "but not to, the new point."

? "To dynamically rubber-band"

? "the line; left-click-hold,"

? "and move the mouse."

? "Uses ''binomial probability"

? "distribution'', a.k.a.,"

? "''Pascal''s Triangle''."

? "''q'' to quit"

dim P1(1) '' end-point #1

dim P2(1) '' #2

dim Cp(1) '' control-point

dim Bp(1) '' Bezier-curve point

pen on '' pick 2 points

gosub WaitForPen

P1(0)=pen(4) '' end-point #1

P1(1)=pen(5)

circle P1(0), P1(1), 3 color 12

gosub WaitForPen

P2(0)=pen(4) '' end-point #2

P2(1)=pen(5)

circle P2(0), P2(1), 3 color 10

repeat

gosub WaitForPen

cls

'' control-point

Cp(0)=pen(4)

Cp(1)=pen(5)

circle P1(0), P1(1), 3 color 12

circle P2(0), P2(1), 3 color 10

circle Cp(0), Cp(1), 3 color 9

pset P1(0), P1(1)

'' calculate, plot Bezier curve

'' uses Pascal''s Triangle

for t=0.05 to 1 step 0.05

s=1-t

k1=s*s

k2=2*s*t

k3=t*t

for i=0 to 1

Bp(i)=k1*P1(i)+k2*Cp(i)+k3*P2(i)

next i

line Bp(0), Bp(1)

next t

line P2(0), P2(1)

k=inkey

until k="q"

pen off

end

label WaitForPen

while pen(0)=0

k=inkey

if k="q" then end

wend

return'