[Richard Suchenwirth] 2005-12-22 - The title says it all. Drawing lines in [Tk] is of course easiest in a [canvas], but sometimes you might need to modify [photo] images, e.g. used for buttons or labels. The following function allows to draw a straight line (and, by repeated application, unfilled polygons) of selectable color (default: black) and width (default: 1).

 proc photo'line {im x0 y0 x1 y1 args} {
    array set "" {-color black -width 1}
    array set "" $args
    set dx [expr {$x1-$x0}]
    set dy [expr {$y1-$y0}]
    set dw [expr {$(-width)/2.}]
    if {abs($dx)>abs($dy)} {
        set d [expr {double($dy)/$dx}]
        for {set x $x0} {$x<=$x1} {incr x} {
            $im put $(-color) \
                -to $x            [expr {round($y0-$dw)}] \
                    [expr {$x+1}] [expr {round($y0+$dw)}]
            set y0 [expr {$y0 + $d}]
        }
    } else {
        set d [expr {double($dx)/$dy}]
        for {set y $y0} {$y<=$y1} {incr y} {
            $im put $(-color) \
                -to [expr {round($x0-$dw)}] $y \
                    [expr {round($x0+$dw)}] [expr {$y+1}]
            set x0 [expr {$x0 + $d}]
        }
    }
 }
#-- Testing:
 package require Tk
 pack [canvas .c]
 set im [image create photo]
 $im put white -to 0 0 100 100
 .c create image 5 5 -image $im -anchor nw
 photo'line $im 10 10 90 10 -color red -width 2
 photo'line $im 10 10 90 90 -color green
 photo'line $im 10 10 10 90 -color blue -width 3

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[Category Graphics] | [Arts and crafts of Tcl-Tk programming]