if 0 {[Richard Suchenwirth] 2005-05-17 - In a few leisurely minutes at work, I hacked together these few LOC that give you kind of a starfield animation by scaling ovals on a [canvas] :) Featuritis demanded different colors, and user-controllable speed ( and cursor keys), but it's still pretty small. [http://mini.net/files/stars.jpg] } package require Tk proc stars'go {c factor} { set w [winfo width $c] set h [winfo height $c] $c scale all [expr {$w/2}] [expr {$h/2}] $factor $factor foreach item [$c find all] { if {[llength [$c bbox $item]] == 0} {$c delete $item; continue} ;# (1) foreach {x0 y0 x1 y1} [$c bbox $item] break if {$x1<0 || $x0>$w || $y1<0 || $y0>$h} {$c delete $item} } time { set x [expr {rand()*$w}] set y [expr {rand()*$h}] set col [lpick {white yellow beige bisque cyan}] $c create oval $x $y [expr {$x+1}] [expr {$y+1}] -fill $col \ -outline $col } 10 after $::ms [info level 0] } proc lpick list {lindex $list [expr {int(rand()*[llength $list])}]} #-- Let's go! pack [canvas .c -bg black] -fill both -expand 1 set ms 40 bind . {incr ms -5} bind . {incr ms 5} stars'go .c 1.05 if 0 { ---- Neat, but I flew through a star and it crashed. Will have to add code to protect against the ovals from getting too large. [Earl Johnson] - [RS]: How did it crash? If a star starts exactly from the centre, it will grow very big - but be deleted when it exceeds one of the canvas boundaries. After more testing I have not been able to reproduce the problem. I guess that what I saw was what [MAK] saw but it just happen to happen while I was flying through a sun. [Earl Johnson] [MAK] can't read "x1": no such variable can't read "x1": no such variable while executing "if {$x1<0 || $x0>$w || $y1<0 || $y0>$h} {$c delete $item}" (procedure "stars'go" line 7) invoked from within "stars'go .c 1.05" ("after" script) [RS]: Interesting - that means there was a canvas item with an empty bounding box, so the foreach {x0 y0 x1 y1} [$c bbox $item] break command didn't set any of these four variables. This is documented in the [canvas] man page: "If no items match any of the tagOrId arguments or if the matching items have empty bounding boxes (i.e. they have nothing to display) then an empty string is returned." Thanks for the hint (though I still don't understand why an oval should have nothing to display...) Added a safety belt, see #(1) above. [MG] thinks there's a mistake in your change - should that ''$c delete item'' be ''$c delete $item''? [RS]: Oops - fixed.. as I couldn't reproduce the problem, this line was never tested... ---- Replace the scale with this for a neat effect: set x [$c canvasx [expr {[winfo pointerx $c] - [winfo rootx $c]}]] set y [$c canvasy [expr {[winfo pointery $c] - [winfo rooty $c]}]] $c scale all $x $y $factor $factor ---- [AMG]: That's a bizarre use of [[[time]]], but it's still easier to read than [[[for]]]. :^) [HE]: To my surprise. [[[time]]] uses less chars but is a litte bit slower than [[[for]]]. (bin) 17 % time {time {set a b} 10} 100000 14 microseconds per iteration (bin) 18 % time {for {set n 0} {$n < 10} {incr n} {set a b}} 100000 11 microseconds per iteration ---- [Category Animation] - [Arts and crafts of Tcl-Tk programming]}