Graphics - PDF Explained - page 54

Group Used for Operators

Other painting operators Shading patterns and inline images. sh BI ID EI Do

Text operators Select and show text in various fonts and

ways.

Tc Tw Tz TL Tf Tr Ts Td TD
Tm T* Tj TJ ' '' d0 d1

Marked content and compatibility oper-
ators

Used to demarcate sections of the stream.

MP DP BMC BDC EMC BX EX

The page is rendered by considering each operator and its operands in turn. The
graphics state is maintained throughout, altered by some operators, consulted by oth-
ers. Operands are often numbers, but can be names, dictionaries, or arrays.
The part of the graphics state which would be needed to render our examples, as it may
appear in a typical PDF implementation, is summarized in Table 5-2 .

Table 5-2. Graphics state

Entry Type Initial value

Current transformation matrix matrix The matrix which transforms default user coordinates to device

coordinates

Fill color color Black

Line color color Black

Line width real 1.0

Path join style integer Mitered joins (0)

Cap style integer Square butt caps (0)

Line dash pattern integer array Solid line

Current clipping path path The empty path

Blend mode name or array Normal

Soft mask name or dictionary None

Alpha constant real 1.0 (full opacity)

Alpha source boolean false

Building and Painting Paths
We're using a landscape US Letter page (width 11 inches or 792 points; height 8.5
inches or 612 pts). The PDF coordinate system, by default, has the origin at the lower-
left corner of the page, with x and y increasing rightward and upward, respectively.
Let's use some path construction, stroking, and line attribute operators to build a sim-
ple graphics stream:
100 100 m 300 200 l 700 100 l Move to (100, 100), line to (300, 200), line to (700, 100)
S Stroke the line
8 w Change line width from the default (1.0) to 8.0