Today's pieces of the banner generator puzzle are a couple of scripts to generate backgrounds. We'll start with the most basic one.

I have this script saved as "generate_background_solid.sh":

#!/bin/bash

if [ "$1" ]; then
  SIZE="$1"
else
  echo "USAGE generate_background_solid.sh SIZE (XxY)"
  exit 1
fi

  BGCOLOR=$(./random_line.sh /usr/X11R6/lib/X11/rgb.txt | cut -f 3- | sed 's/[ \t]*//g')
  convert -size $SIZE xc:"$BGCOLOR" background.png

exit 0

...almost self-explanatory. Given an XxY argument, it produces a random solid-color background. "./generate_background_solid.sh 400x100" gets you something like this:

Later on in the project, we'll see how we use Image Magick's 'identify' command to get the size of a banner made with text, so we know how to pass that size argument to the background scripts. Right now, let's deal with a thornier problem, generating a gradient and not having it just be straight up and down.

I have this script saved as "generate_background_gradient.sh":

#!/bin/bash

if [ "$1" ]; then
  SIZE="$1"
else
  echo "USAGE generate_background_gradient.sh SIZE (XxY)"
  exit 1
fi

  FROMCOLOR=$(./random_line.sh /usr/X11R6/lib/X11/rgb.txt | cut -f 3- | sed 's/[ \t]*//g')
  TOCOLOR=$(./random_line.sh /usr/X11R6/lib/X11/rgb.txt | cut -f 3- | sed 's/[ \t]*//g')
  STARTSIZE=$(($(echo $SIZE | awk -Fx '{print $1}')+10))
  STARTSIZE=$STARTSIZE"x"$STARTSIZE

  CONVERTSTRING=" -size ""$STARTSIZE"
  CONVERTSTRING="$CONVERTSTRING"" gradient:""$FROMCOLOR-$TOCOLOR"
  CONVERTSTRING="$CONVERTSTRING"" -rotate ""$(($RANDOM % 360 + 1))"
  CONVERTSTRING="$CONVERTSTRING"" -gravity center -crop ""$SIZE""+0+0"
  CONVERTSTRING="$CONVERTSTRING"" background.png"

  convert $CONVERTSTRING

exit 0

...not nearly as straight-forward as we had hoped. See, first we pick two random colors, then we have to get the 'X' width (the longest dimension) and pad it some, then crop it back down to our expected size. Let's show why we have to do it this way:

If we run:

convert -size 400x100 gradient:red-blue background.png

we get this:

If we want a gradient that goes some other orientation besides straight up and down, we can simply add the '-rotate' option, right?

convert -size 200x50 gradient:red-blue -rotate 45 background.png

But I see a problem:

and cropping it down to the original size doesn't help:

convert -size 200x50 gradient:red-blue -rotate 45 -gravity center -crop 200x50+0+0 background.png

...so what we have to do is generate the gradient at a much larger size, say a square with its size as the widest dimension of the desired banner. How's that working for us?

convert -size 200x200 gradient:red-blue -rotate 75 -gravity center -crop 200x50+0+0 background.png

We almost got away with that! But look closely and you'll see, for this rotation of 75 degrees, we ended up with a corner chipped out of the upper-right and lower-left.

Sooooo, we have to add an extra ten pixels on the border of the square, which we can then crop down to the proper size for a banner background. And that explains all the calisthenics in the script... hopefully.

Running it gives backgrounds like these:

How trendy! We'll explore patterned backgrounds next.