using SpecialFunctions, Plots, LaTeXStrings
gr(grid=false,legend=false,size=(600,250),ylims=(-3,3))

## functions
fp(x) = gamma(x) > 0.0 ? gamma(x) : NaN
fn(x) = gamma(x) < 0.0 ? gamma(x) : NaN
g(x,s) = 1+s*(x-1) # linear ramp
gp(x,s) = g(x,s)*fp(x)
gn(x,s) = g(x,s)*fn(x)

## arrays
x = LinRange(-5.01,5.01,999)
svals = LinRange(0,0.999999,400)
xvals = LinRange(0,0.99899,400)
xa=[zero.(svals);xvals]
sa=[svals;svals[end]*one.(xvals)]

## animate
anim = @animate for (xa,sa) in zip(xa,sa)
    plot(x,[gp.(x .-xa,sa),gn.(x .-xa,sa)],line=(:blue,3,0.5))
    plot!(x,[fp.(x .+1),fn.(x .+1)],line=(:green,1,0.4))
    plot!(x,[fp.(x),fn.(x)],line=(:red,1,0.4))
    annotate!(3.7,2.3,L"\Gamma(x)",fontsize=10)
    annotate!(1.5,2.3,L"x\Gamma(x)",fontsize=10)
    xlabel!(L"x")
end every 5 

gif(anim,"gamma.gif",fps=30)