http://www.xmission.com/~georgeps/images/wiki/shading_a_plane.png
gold testing inhouse pix package require Tk
proc radiate {win px py width height} {
# XXX be aware of this.
$win delete all
set ratio [expr {hypot($px,$py) / 255.0}]
for {set y 0} {$y < $height} {incr y} {
for {set x 0} {$x < $width} {incr x} {
set gray [expr {int(hypot(($x - $px),($y - $py)) * $ratio)}]
if {$gray > 255} {
set gray 255
}
set value [expr {255 - $gray}]
set color [format #%2.2x%2.2x%2.2x $value $value $value]
#puts $color
$win create line $x $y [expr {$x + 1}] [expr {$y + 1}] -fill $color -width 1
}
}
}
proc main {argc argv} {
pack [canvas .c -width 400 -height 400 -bg black]
set ::px 200
set ::py 200
pack [frame .fpoint] -fill x
label .fpoint.lx -text X:
entry .fpoint.ex -textvariable ::px
label .fpoint.ly -text Y:
entry .fpoint.ey -textvariable ::py
grid .fpoint.lx -row 0 -column 0
grid .fpoint.ex -row 0 -column 1
grid .fpoint.ly -row 0 -column 2
grid .fpoint.ey -row 0 -column 3
pack [button .b -text Radiate -command {radiate .c $::px $::py 400 400}]
}
main $::argc $::argv