PDF Explained

Chapter 5. Graphics

In this chapter, we’ll run through the main ways to build graphics in the content stream of a PDF page. All of the examples are based on the same PDF we created manually in Chapter 2 and processed into valid PDF documents with pdftk in the same fashion. All the examples are included in the online resources.

Looking at Content Streams

A PDF page is made up of one or more content streams, defined by the /Contents entry in the page object, together with a shared set of resources, defined by the /Resources entry. In all our examples, there will only be a single content stream. Multiple content streams are equivalent to a single stream containing their concatenated content.

Here’s an example page, with no resources and a single content stream:

3 0 obj
<<
  /Type /Page
  /Parent 1 0 R
  /Resources << >>
  /MediaBox [ 0 0 792 612 ]
  /Rotate 0
  /Contents [ 2 0 R ]
>>
endobj

Here’s the associated content stream, consisting of the stream dictionary and the stream data.

2 0 obj
<< /Length 18 >> Stream dictionary
stream
200 150 m 600 450 l S Stream data
endstream
endobj

We’ll discover what the m, l and S operators do in a moment. The numbers are measurements in points—a point (or pt) is 1/72 inch. The result of loading this document into a PDF viewer (after processing with pdftk as per Chapter 2) is shown in Figure 5-1.

The full manually created file (before processing with pdftk) is shown in Example 5-1. We’re going to be using variations on this file for the rest of this chapter. For the ...