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# aniwave.tcl -- # # This demonstration script illustrates how to adjust canvas item # coordinates in a way that does something fairly similar to waveform # display. if {![info exists widgetDemo]} { error "This script should be run from the \"widget\" demo." } package require Tk set w .aniwave catch {destroy $w} toplevel $w wm title $w "Animated Wave Demonstration" wm iconname $w "aniwave" positionWindow $w label $w.msg -font $font -wraplength 4i -justify left -text "This demonstration contains a canvas widget with a line item inside it. The animation routines work by adjusting the coordinates list of the line; a trace on a variable is used so updates to the variable result in a change of position of the line." pack $w.msg -side top ## See Code / Dismiss buttons set btns [addSeeDismiss $w.buttons $w] pack $btns -side bottom -fill x # Create a canvas large enough to hold the wave. In fact, the wave # sticks off both sides of the canvas to prevent visual glitches. pack [canvas $w.c -width 300 -height 200 -background black] -padx 10 -pady 10 -expand yes # Ensure that this this is an array array set animationCallbacks {} # Creates a coordinates list of a wave. This code does a very sketchy # job and relies on Tk's line smoothing to make things look better. set waveCoords {} for {set x -10} {$x<=300} {incr x 5} { lappend waveCoords $x 100 } lappend waveCoords $x 0 [incr x 5] 200 # Create a smoothed line and arrange for its coordinates to be the # contents of the variable waveCoords. $w.c create line $waveCoords -tags wave -width 1 -fill green -smooth 1 proc waveCoordsTracer {w args} { global waveCoords # Actual visual update will wait until we have finished # processing; Tk does that for us automatically. $w.c coords wave $waveCoords } trace add variable waveCoords write [list waveCoordsTracer $w] # Basic motion handler. Given what direction the wave is travelling # in, it advances the y coordinates in the coordinate-list one step in # that direction. proc basicMotion {} { global waveCoords direction set oc $waveCoords for {set i 1} {$i<[llength $oc]} {incr i 2} { if {$direction eq "left"} { lset waveCoords $i [lindex $oc \ [expr {$i+2>[llength $oc] ? 1 : $i+2}]] } else { lset waveCoords $i \ [lindex $oc [expr {$i-2<0 ? "end" : $i-2}]] } } } # Oscillation handler. This detects whether to reverse the direction # of the wave by checking to see if the peak of the wave has moved off # the screen (whose size we know already.) proc reverser {} { global waveCoords direction if {[lindex $waveCoords 1] < 10} { set direction "right" } elseif {[lindex $waveCoords end] < 10} { set direction "left" } } # Main animation "loop". This calls the two procedures that handle the # movement repeatedly by scheduling asynchronous calls back to itself # using the [after] command. This procedure is the fundamental basis # for all animated effect handling in Tk. proc move {} { basicMotion reverser # Theoretically 100 frames-per-second (==10ms between frames) global animationCallbacks set animationCallbacks(simpleWave) [after 10 move] } # Initialise our remaining animation variables set direction "left" set animateAfterCallback {} # Arrange for the animation loop to stop when the canvas is deleted bind $w.c <Destroy> { after cancel $animationCallbacks(simpleWave) unset animationCallbacks(simpleWave) } # Start the animation processing move
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