require 'ruby2d'
s1 = Square.new(x: 0, y: 0, size: 100, color: 'white')
s2 = Square.new(x: 100, y: 100, size: 50, color: 'green')
c = 0.0
switch = true
update do
if switch
c += 0.01
if c > 1.0
switch = false
end
else
c -= 0.01
if c < 0.0
switch = true
end
end
s1.color = [1, 1, 1, c]
end
show