better documentation on how to use with prawn

[jpaas]

Through some trial and error and clues left hanging in the interwebs, I only got it to work as follows by using to_png...

barcode = PDF417.new("my data to encode")
data = StringIO.new(barcode.to_png)
pdf.image(data)

[jpaas]

Another tip... I wanted to centre the barcode in the PDF, and then advance my cursor afterwards. So by looking at the code I saw how the width is calculated...

x_scale = 2
y_scale = 10
margin = 0
barcode = PDF417.new("my data to encode")
data = StringIO.new(barcode.to_png(margin: margin, x_scale: x_scale, y_scale: y_scale))
barcode_width = barcode.bit_columns * x_scale + margin * 2 
image = pdf.image(data, at: [(pdf.bounds.width - barcode_width) / 2, pdf.cursor])
pdf.move_down(image.height)

[Xosmond]

On my case I just did this on prawn document:

barcode = StringIO.new(PDF417.new("my data to encode").to_png)
image barcode, width: 200, height: 35

Because i don't need special coordinates.