source: liacs/mms/project/chessboard.pl@ 74

#!/usr/bin/env perl
# Build a full screen black/white checkerboard using imagemagick (the hard way)
# Rick van der Zwet, 2009
$BLOCK_SIZE=100;

($WIDTH, $HEIGHT) = split(' ',`xrandr  | awk '/\\*/ {print $$1}' | tr 'x' ' '`);
print "Screen: ". $WIDTH . "x" . $HEIGHT . "\n";

$HEIGHT=600;
$WIDTH=800;

$X_NUM=$HEIGHT/$BLOCK_SIZE;
$Y_NUM=$WIDTH/$BLOCK_SIZE;

$X_NUM--;
$Y_NUM--;

print "Blocks x,y: " . $X_NUM . "," . $Y_NUM . "\n";

$FILE='chessboard.gif';
#`convert -size 640x480 pattern:checkerboard -monochrome gif:$FILE`;
#`display gif:$FILE` ;

$SIZE=" -size ${BLOCK_SIZE}x${BLOCK_SIZE}";

$LINE = [];

$COLOR="black";
$LINESTART="black";
sub blockswap() {
    if ($COLOR eq "black") {
        $COLOR = "white";
    } else {
        $COLOR = "black";
    }
}

sub newline() {
    if ($LINESTART eq "black") {
        $LINESTART = "white";
    } else {
        $LINESTART = "black";
    }
    $COLOR=$LINESTART;
}

for($i = 0; $i < $X_NUM; $i++) {
    for($j =0; $j < $Y_NUM; $j++) {
        print "Block $i,$j\n";
        $LINE[$i] = $LINE[$i] . $SIZE . " xc:$COLOR";
        blockswap();
    }    
    newline();
}

for($i = 0; $i < $X_NUM; $i++) {
    $LINE[$i] = " \\(" . $LINE[$i] . " +append \\) -append ";
}

$CMD = "convert" . join("  ",@LINE) . " gif:$FILE";
print $CMD;
`$CMD`;