[Arjen Markus] I needed a script to move and scale the contents of a canvas. [RS] suggested that this can be achieved with a few event bindings. He, of 
course, was right as usual. It is slightly more complicated than one-line commands, 
but still, it can hardly be easier.

''Notes:''
   * In the actual script I use so-called world coordinates to transform metric coordinates to and from pixel coordinates. So the procedures get more complicated to update the transformation data.
   * If the number of items gets large (a few hundred or a few thousand, as in my case), you can notice a delay between the updates. I use a slightly different method for this situation - control-arrow-keys to shift it a known number of pixels. But the principle stays the same.


----
 # Eperiment with scale/move items in a canvas
 #
 proc moveItems { x y } {
    global xc yc
    
    if { [info exists ::xc] } {
       .c move all [expr {$x-$xc}] [expr {$y-$yc}]
    }   
    set xc $x
    set yc $y
 }

 proc scaleItems { type x y } {
   
    if { $type == "+" } {
       .c scale all $x $y [expr {sqrt(2.0)}] [expr {sqrt(2.0)}]
    } else {
       .c scale all $x $y [expr {1.0/sqrt(2.0)}] [expr {1.0/sqrt(2.0)}]
    }  
 }

 pack [canvas .c -bg white] -fill both

 .c create oval 0 0 100 100 -fill red -outline black -width 4
 .c create rectangle 200 200 300 300 -fill green -outline yellow
 .c create line 0 200 200 0 -fill black -width 10
 .c create line 0 -200 -200 0 -fill blue -width 6

 set xc 0
 set yc 0
 focus .c 
 bind .c <Button-1> {set xc %x; set yc %y} 
 bind .c <B1-Motion> {moveItems %x %y}
 bind .c <KeyPress-a> {scaleItems + %x %y}
 bind .c <KeyPress-b> {scaleItems - %x %y}
 bind .c <Control-KeyPress-plus> {scaleItems + %x %y}
 bind .c <Control-KeyPress-minus> {scaleItems - %x %y}
----

See also [Canvas zooming]

[[
[Category Graphics]
]]