Atlantis Cafe Illusion
GWM The Atlantis Cafe was a greasy spoon Cafe in Bristol. Professor Richard Gregory published a paper based on the illusion created by the tiles on the front of the cafe [L1 ].
See also Bulging Line Illusion Arrow Illusion.
This application allows you to control some of the parameters of the tiling.
PT: You can now see the actual site in Google street view now that they have driven around Bristol. See [L2 ]
The relative luminance of the mortar should be midway between the brightness of the light & dark tiles for the illusion to occur most strongly; this toyol (half way between a toy and a tool) could allow you to experiment with the degree of illusion.
{Copy this code into Wish console and run it. 2 scale controls control the offset of the tiles and the lightness of the grouting.}
GWM 26.10.04 Minor change to remove some unused variables. KJN 2008-10-17 remove some corrupted text
Jeff Smith 2020-09-01 : Below is an online demo using CloudTk. This demo runs "Atlantis Cafe Illusion" in an Alpine Linux Docker Container. It is a 27.4MB image which is made up of Alpine Linux + tclkit + Atlantis-Cafe-Illusion.kit + libx11 + libxft + fontconfig + ttf-linux-libertine. It is run under a user account in the Container. The Container is restrictive with permissions for "Other" removed for "execute" and "read" for certain directories.
# Atlantis Cafe effect - first reported by Prof Richard Gregory
# see http://www.richardgregory.org/papers/cafe_wall/cafe-wall.doc
# then at Bristol University, UK. The Atlantis Cafe was at the bottom of St Michael's Hill
# but has now changed hands and lost the tiles. So, here they are again!
# The luminance of the mortar between tiles affects the degree of illusion, as does
# placing the tiles at the bottom of the screen and looking at the top of screen (peripheral vision).
# The degree of overlap of the tiles also affects the degree of illusion.
proc makerow {rowdata length height repeat colmort coldark collight} { ;# make an image data set
# of bricks/tiles length by height, repeating every repeat along length.
# colmort etc are 3 colours for mortar, dark tile light tile
set tilelen [expr $repeat/2]
for {set j 0} {$j<$height} { incr j} { ;# rows of picture
set pix [list]
for {set i 0} {$i<$length} { incr i } {
if {$j<2} { lappend pix $colmort
} else {
if {[expr $i%$repeat<$tilelen-1]} { lappend pix $coldark
} elseif {[expr $i%$repeat>($tilelen+1) && $i%$repeat<$repeat-2]} {
lappend pix $collight
} else { lappend pix $colmort
}
}
}
$rowdata put [list $pix] -to 0 $j
}
}
proc mortar {ht size lumfrac} { ;# set mortar colour
set colmo [format %02x [expr int($lumfrac*2.55)] ]
makerow tilerow $size $ht 60 \#$colmo$colmo$colmo \#000000 \#ffffff
}
proc movetiles {ht frac} { ;# slide rows of tiles across the canvas
catch [destroy .frm] {} ;# delete it. Same as clear.
set frm [canvas .frm -width [expr 8*$ht] -height [expr 8*$ht] ]
for {set j 0} {$j<8} { incr j} { ;# rows of tiles
if {[expr $j%2]} {set dx $frac
} else { set dx 0}
label $frm.row$j -image tilerow -bd 0 -relief raised
place $frm.row$j -x $dx -y [expr $j*$ht]
}
pack .frm
}
proc setup {size} {
catch [destroy .dt] {} ;# delete it. Same as clear.
catch [destroy .dlum] {} ;# delete it. Same as clear.
wm title . "Atlantis Cafe"
set ht [expr $size/16]
scale .dt -variable frac -orient horizontal -label "fraction" -command "movetiles $ht"
scale .dlum -variable lumf -orient horizontal -label "mortar luminance" -command "mortar $ht $size"
image create photo tilerow -height $ht -width $size
pack .dt .dlum -side top
}
global frac lumf
set frac 10
set lumf 50
setup 450