Tile Test:

REBOL []
 
img: load-image http://reb4.me/r/anim/gradient-cyan.png
 
x-layout: layout [
    btile: backtile img effect [tile]
    btn "Rebol Button"
]
 
plugin-size: does [
    as-pair do-browser "document.getElementById('tile-obj').offsetWidth;"
    do-browser "document.getElementById('tile-obj').offsetHeight;"
]
 
page-margin: does [
    as-pair do-browser "document.body.offsetLeft;"
    do-browser "document.body.offsetTop;"
]
 
plugin-offset: does [
    as-pair do-browser "document.getElementById('tile-obj').offsetLeft;"
    do-browser "document.getElementById('tile-obj').offsetTop;"
]
 
do resize: has [size][
    x-layout/size: size: plugin-size
    btile/size: plugin-size + plugin-offset + page-margin
    btile/offset: 0x0 - plugin-offset - page-margin
    show x-layout
]
 
insert-event-func [switch event/type [resize [resize]] event]
 
view x-layout