Tk canvas item --- outline issue

Feb. 22, 2009 by Zhuo

概要 // Abstract

• Tkのcanvas itemが正確にどのようにpixelを占めるか．
• とくに，widthを指定した際，outlineはどのようにpixelを占めるか．
• itemを指定して coords , bbox を指定した場合どの座標が得られるか．
• itemにEnter/Leaveイベントをバインドした場合，どのpixelへの進入をもってイベントが発生するか．

• Which pixels in the canvas are occupied by a Tk canvas item, exactly?
• Particularly, which pixels in the canvas are occupied by an outline area, when the width option is specified ?
• Which pixel locations are obtained when a query is made on an item using coords / bbox ?
• Which pixel, when entered/left, throws an Enter/Leave event when the preceding bind command specifies to do so?

Sample Code

# tkCanvasItemOutline.tcl
console show
canvas .c -width 480 -height 480 -bg black
pack .c 

bind . q {destroy .}
bind .c  {showDot .c %x %y}
bind .c  {moveDot .c %x %y}
bind .c  {hideDot .c}

set ::prevcx ""
set ::prevcy ""

proc showDot {c x y} {
    set cx [$c canvasx $x]
    set cy [$c canvasy $y]
    $c create line $cx [expr $cy-5] $cx [expr $cy+6] -fill green -width 1 -tags cur -state disabled
    $c create line [expr $cx-5] $cy [expr $cx+6] $cy -fill green -width 1 -tags cur -state disabled
    set ::prevcx $cx
    set ::prevcy $cy
}

proc moveDot {c x y} {
    set cx [$c canvasx $x]
    set cy [$c canvasy $y]
    set dx [expr $cx - $::prevcx]
    set dy [expr $cy - $::prevcy]
    $c move cur $dx $dy
    set ::prevcx $cx
    set ::prevcy $cy
}

proc hideDot {c} {
    $c delete cur
}



#canvas item test:
for { set wi 0 } { $wi < 10 } {incr wi} {
    set testitem [.c  create rectangle [expr 120+$wi*20] 100 [expr 139+$wi*20] 110 -width $wi -outline red -fill blue]
    .c bind $testitem  {putCanvXY .c %x %y enter}
    .c bind $testitem  {putCanvXY .c %x %y motion}
    .c bind $testitem  {putCanvXY .c %x %y leave}
    puts "horiz: wi=$wi: coords: [.c coords $testitem]; bbox: [.c bbox $testitem]"
}

for { set wi 0 } { $wi < 10 } {incr wi} {
    set testitem [.c  create rectangle 70 [expr 150+$wi*20] 80 [expr 169+$wi*20] -width $wi -outline red -fill blue]
    .c bind $testitem  {putCanvXY .c %x %y enter}
    .c bind $testitem  {putCanvXY .c %x %y motion}
    .c bind $testitem  {putCanvXY .c %x %y leave}
    puts "vert:  wi=$wi: coords: [.c coords $testitem]; bbox: [.c bbox $testitem]"
}


proc putCanvXY {c x y str} {
    puts "cx: [$c canvasx $x] cy: [$c canvasy $y] ($str)"
}

Experiment

• ActiveTcl 8.4.17
• Windows XP Professional SP2

Result1: screen shot

Result2: width option, coords/bbox, cx for Enter

width option
d1
d2
coords
x0 y0 x1 y1
bbox
x0 y0 x1 y1
actual outline coverage
cx for Enter event
0
0
0
70 150 80 169
69 149 81 170
(no outline. body:70-80)
69-81
1
1
1
70 170 80 189
69 169 81 190
70-70, 81-81
69-81
2
1
1
70 190 80 209
69 189 81 210
69-70, 80-81 
68-82
3
2
3
70 210 80 229
68 208 82 231
69-71, 80-82
68-82
4
2
3
70 230 80 249
68 228 82 251
68-71, 79-82
67-83
5
3
5
70 250 80 269
67 247 83 272
68-72, 79-83
67-83
6
3
5
70 270 80 289
67 267 83 292
67-72, 78-83
66-84
7
4
7
70 290 80 309
66 286 84 313
67-73, 78-84
66-84
8
4
7
70 310 80 329
66 306 84 333
66-73, 77-84
65-85
9
5
9
70 330 80 349
65 325 85 354
66-74, 77-85
65-85