#!/bin/sh
#
# Usage: display_virtual input [output]
#
# overlay image on a centered virtual canvas suronding actual image with a
# blue box, and drawing a red cross at the 0,0 origin.
#
S=200  # output image size

C=`expr $S / 2`
C1=`expr $C - 10`
C2=`expr $C + 10`

convert "$1" \
    -compose copy -bordercolor blue -border 1x1 -repage -1-1\! \
    +compose -crop ${S}x${S}-${C}-${C}\! -background lightblue -flatten \
    -draw "fill red  path 'M $C,$C1 $C,$C2  M $C1,$C $C2,$C'" \
    "${2:-"x:"}"