Convert rectangle(s) to polygons, also refer to [Canvas Rotation]
 # Note: a new object ID will be assigned after conversion - may affect visibility order with respect
 #    to other objects.
 #    This may be prevented when conversion is part of a proc that saves canvas content to a file
 #    (and then restores it - requires modified proc without $w delete and append "$w create poly" text
 #    to file output).
 #    This routine currently converts with the most common item attributes
 proc rect2poly {w item} {
     foreach {x0 y0 x1 y1} [$w coords $item] {
         set outline [$w itemcget $item -outline]
         set width [$w itemcget $item -width]
         if {!$width} {
             set outline {}
         }
         set fill [$w itemcget $item -fill]
         $w delete $item
         $w create poly $x0 $y0 $x0 $y1 $x1 $y1 $x1 $y0 -fill $fill -outline $outline -width $width
     }
 }
 
 proc rect2poly_all {w} {
     foreach item [$w find all] {
             puts $item
         if {[$w type $item]=="rectangle"} {
             rect2poly $w $item
         }
     }
 }
 
 # general notes:
 #   -outline defaults to empty with polys, but black with rects
 #   -width 0 yields 1 with polys, so making an outline absent, -outline must be ""
 #   -fill is by default not present with rects, for rectangles, "" must be specified
 #   poly creation with rect defaults:
 #   .c create rectangle 5 50 150 150 -fill "" -outline black
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[Category Graphics]