vmdrc

menu main on
foreach {x y} [ menu main loc ] {}
menu main move [expr $x+510] $y

proc sigmoidal { x alpha x0 } {
    set val [expr ($x-$x0) / sqrt($alpha*$alpha+($x-$x0)*($x-$x0)) + 1 ]
    return $val
}

proc interpolate_AB { col1 col2 frac } {
    # for linear interpolation
    set frac_step [ expr $frac*0.5 ]
    # for sigmoidal interpolation
    set alpha 0.5
    set x0 0.5
    set sx [ sigmoidal [ expr $frac/0.5 ] $alpha $x0 ]
    set s1 [ sigmoidal 1.0 $alpha $x0 ]
    set s0 [ sigmoidal 0.0 $alpha $x0 ]
    set frac_step [ expr ($sx - $s0)/($s1 - $s0) ]
    set delta [vecsub $col2 $col1]
    set vect [vecadd $col1 [vecscale $delta $frac_step]]
    return $vect
}

proc colorscale_sigmoidal_and_errors {} {
    display update off
    set mincolorid [ expr [colorinfo num] -1 ]
    set maxcolorid [ expr [colorinfo max] -1 ]
    set colrange [ expr $maxcolorid - $mincolorid ]
    set colhalf [ expr $colrange / 2]
    set alpha { 0.0 0.0 1.0 } 
    set beta { 1.0 0.0 0.0 } 
    set gamma { 0.0 1.0 0.0 } 
    for { set i $mincolorid} {$i < $maxcolorid} {incr i} {
        set colfrac [ expr ($i - $mincolorid) / double($colrange) ]
        # here's where you actually implement the piecewise function you'll
        # be using
        if { $colfrac < 0.5 } {
            set colorvect [ interpolate_AB $alpha $beta $colfrac ]
        } elseif { $colfrac > 0.95 } {
            set colorvect $gamma
        } else {
            set colorvect $beta
        }
        foreach {r g b} $colorvect {}
        display update ui
        #puts "index: $i $r $g $b -- $colfrac"
        color change rgb $i $r $g $b
    }
    display update on
}

proc white_bg_2d {} {
    display projection orthographic
    color Display Background white
    axes location off
}