Using canvas sizes with ... exceptional widths can bring some surpises. The following pieces of code show how from a working test sample that was used to check whether some things are possible in Tcl or not. First, two helper scripts that get loaded in all three examples: # ScrolledCanvas.tcl is a scrollable canvas using standard techniques # as described for example in Brent B. Welch's book "Practical # Programming in Tcl and Tk" proc ScrolledCanvas {c args} { frame $c eval {canvas $c.canvas \ -xscrollcommand [list $c.xscroll set] \ -yscrollcommand [list $c.yscroll set] \ -highlightthickness 0 \ -borderwidth 0} $args scrollbar $c.xscroll -orient horizontal \ -command [list $c.canvas xview] scrollbar $c.yscroll -orient vertical \ -command [list $c.canvas yview] grid $c.canvas $c.yscroll -sticky news grid $c.xscroll -sticky ew grid rowconfigure $c 0 -weight 1 grid columnconfigure $c 0 -weight 1 return $c.canvas } and # Drawer.tcl will drop a few objects (arrows etc.) onto a canvas proc DrawLeftMark {canvas color {width ""} {height ""}} { if {$height == ""} { set h [$canvas cget -height] } else { set h $height } set x1 0 set x2 [expr {$h - 1}] set x3 [expr {($h * 4) - 1}] set y1 0 set y5 [expr {$h - 1}] set y3 [expr {($y1 + $y5) / 2}] set y2 [expr {$y3 - ($h / 4)}] set y4 [expr {$y3 + ($h / 4)}] $canvas create polygon \ $x1 $y3 $x2 $y1 $x2 $y2 $x3 $y2 $x3 $y4 $x2 $y4 $x2 $y5 $x1 $y3 \ -fill $color \ -outline black } proc DrawRightMark {canvas color {width ""} {height ""}} { if {$width == ""} { set w [$canvas cget -width] } else { set w $width } if {$height == ""} { set h [$canvas cget -height] } else { set h $height } set x1 [expr {$w - 1}] set x2 [expr {$w - $h - 1}] set x3 [expr {$w - ($h * 4) - 1}] set y1 0 set y5 [expr {$h - 1}] set y3 [expr {($y1 + $y5) / 2}] set y2 [expr {$y3 - ($h / 4)}] set y4 [expr {$y3 + ($h / 4)}] $canvas create polygon \ $x1 $y3 $x2 $y1 $x2 $y2 $x3 $y2 $x3 $y4 $x2 $y4 $x2 $y5 \ -fill $color \ -outline black } proc DrawTicks {canvas {width ""}} { if {$width == ""} { set w [$canvas cget -width] } else { set w $width } set lm 0 set rm $w set tickSpace [expr {$w / 1000}] if {$tickSpace < 200} {set tickSpace 200} for {set x $lm} {$x <= $rm} {incr x $tickSpace} { $canvas create text $x 0 -text $x -anchor nw } } Now for the first example: draw a simple canvas with 800 million pixels and drop a few objects on that. This example will work flawlessly: source ScrolledCanvas.tcl source Drawer.tcl # The following code for a simple canvas works fine for "small" # scroll regions and for "large" scroll regions #set scrollWidth 20000 set scrollWidth 800000000 set scrollHeight 400 set rowHeight 20 # Create a ScrolledCanvas and setup its scroll region set sc [ScrolledCanvas .c -width 400 -height 200] $sc configure -scrollregion "0 0 $scrollWidth $scrollHeight" # Make the ScrollableWindow visible pack .c -fill both -expand true DrawLeftMark $sc yellow $scrollWidth $rowHeight DrawRightMark $sc yellow $scrollWidth $rowHeight DrawTicks $sc $scrollWidth # Show the canvas coordinates of the mouse pointer for # validation set location [label .location -textvariable cur_x_y] pack .location bind Canvas {ShowLocation %W %x %y} bind Canvas {set cur_x_y ""} proc ShowLocation {w x y} { global cur_x_y set cx [expr int([$w canvasx $x])] set cy [expr int([$w canvasy $y])] set cur_x_y "x = $cx , y = $cy" } So, if that works, packing some canvases together in one frame to scroll them should work too, right? Nope, sorry, it wont: # Demo program for the creation of a scrollable multi row canvas # using native Tcl/Tk methods source ScrolledCanvas.tcl source Drawer.tcl # The following code works fine for "small" scroll regions, # but runs into problems with "large" scroll regions. Try, # for example, a scroll width of 40,000 pixel (let alone # 800,000,000 pixel). # Windows will exit abnormally, running under Linux (albeit # with a display on Solaris) gives different effects for # different lengths ... objects not shown, canvas too small etc.) set scrollWidth 40000 #set scrollWidth 800000000 set scrollHeight 400 set rowHeight 20 # Create a ScrolledCanvas and setup its scroll region set sc [ScrolledCanvas .c -width 400 -height 200] $sc configure -scrollregion "0 0 $scrollWidth $scrollHeight" # Create a frame widget within the ScrolledCanvas, which # will serve as a container for the individual rows set sf [frame $sc.f] $sc create window 0 0 -anchor nw -window $sf # Make the ScrolledCanvas visible. pack .c -fill both -expand true # Create some rows (canvas widgets) for displaying data... set row1 [canvas $sf.c1 \ -width $scrollWidth \ -height $rowHeight \ -highlightthickness 0 \ -bg lightyellow] DrawLeftMark $row1 yellow $scrollWidth $rowHeight DrawRightMark $row1 yellow $scrollWidth $rowHeight DrawTicks $row1 $scrollWidth set row2 [canvas $sf.c2 \ -width $scrollWidth \ -height $rowHeight \ -highlightthickness 0 \ -bg orange] DrawLeftMark $row2 brown DrawRightMark $row2 brown DrawTicks $row2 set row3 [canvas $sf.c3 \ -width $scrollWidth \ -height $rowHeight \ -highlightthickness 0 \ -bg lightgreen] DrawLeftMark $row3 green DrawRightMark $row3 green DrawTicks $row3 set row4 [canvas $sf.c4 \ -width $scrollWidth \ -height $rowHeight \ -highlightthickness 0 \ -bg pink] DrawLeftMark $row4 red DrawRightMark $row4 red DrawTicks $row4 # ... and put them into the ScrolledCanvas. grid $row1 -row 0 grid $row2 -row 1 grid $row3 -row 2 grid $row4 -row 3 # swap row2 and row3: #grid $row2 -row 2 #grid $row3 -row 1 # hide row2: #grid forget $row2 # Show the canvas coordinates of the mouse pointer for # validation set location [label .location -textvariable cur_x_y] pack .location bind Canvas {ShowLocation %W %x %y} bind Canvas {set cur_x_y ""} proc ShowLocation {w x y} { global cur_x_y set cx [expr int([$w canvasx $x])] set cy [expr int([$w canvasy $y])] set cur_x_y "x = $cx , y = $cy" } The question is now: why?