View Source Pdf.Reader.GraphicsState (ExPDF v1.0.1)

Struct and operations for the PDF graphics state during content stream interpretation.

CTM (current transformation matrix) and text matrices are stored as 6-float tuples {a, b, c, d, e, f} — the affine subset used by PDF (§8.3.3 of the PDF spec). Full 4×4 matrices are NOT used; PDF only needs the 2D affine form.

The :stack holds snapshots pushed by the q operator and restored by Q.

Text state additions (§ 9.4.4)

The :widths_fn field holds the per-glyph width closure for the active font. It is set by the Tf operator handler and used by advance_tm/2 to compute exact horizontal text advance per the full § 9.4.4 formula. When nil, advance defaults to 0 per glyph (only Tc, Tw, and Tfs terms contribute).

Matrix convention

PDF uses the row-vector convention (§ 8.3.3):

| a b 0 |
| c d 0 |
| e f 1 |

Multiplication: M3 = M1 × M2 with formulas:

a3 = a1*a2 + b1*c2
b3 = a1*b2 + b1*d2
c3 = c1*a2 + d1*c2
d3 = c1*b2 + d1*d2
e3 = e1*a2 + f1*c2 + e2
f3 = e1*b2 + f1*d2 + f2

Summary

Types

matrix()

t()

Functions

multiply(arg1, arg2)

Multiplies two affine matrices under the PDF row-vector convention.

new()

Returns a fresh GraphicsState with identity matrices and zeroed text state.

pop(state)

Pops the most-recently-pushed graphics state from :stack (implements PDF Q operator).

push(state)

Pushes the current graphics state onto :stack (implements PDF q operator).

Types

matrix()

@type matrix() :: {float(), float(), float(), float(), float(), float()}

t()

@type t() :: %Pdf.Reader.GraphicsState{
  char_spacing: float(),
  ctm: matrix(),
  font: nil | binary(),
  font_size: float(),
  horizontal_scaling: float(),
  leading: float(),
  rise: float(),
  stack: [t()],
  tlm: matrix(),
  tm: matrix(),
  widths_fn: nil | (binary() -> [non_neg_integer()]),
  word_spacing: float()
}

Functions

multiply(arg1, arg2)

@spec multiply(matrix(), matrix()) :: matrix()

Multiplies two affine matrices under the PDF row-vector convention.

multiply(m1, m2) returns M3 = M1 × M2. Both arguments and the result are 6-element {a, b, c, d, e, f} tuples.

Spec reference: PDF 1.7 § 8.3.4.

new()

@spec new() :: t()

Returns a fresh GraphicsState with identity matrices and zeroed text state.

pop(state)

@spec pop(t()) :: t()

Pops the most-recently-pushed graphics state from :stack (implements PDF Q operator).

If the stack is empty (malformed stream), this is a silent no-op — the interpreter remains in the current state rather than crashing. Spec allows senders to have unbalanced q/Q in practice (e.g. content streams generated without strict nesting).

push(state)

@spec push(t()) :: t()

Pushes the current graphics state onto :stack (implements PDF q operator).

The full state struct is saved. No fields are excluded — this keeps semantics consistent with the writer's q/Q discipline.