package psinterpreter

import "github.com/go-text/typesetting/font/cff/interpreter"

Package psinterpreter implement a Postscript interpreter required to parse .CFF files, and Type1 and Type2 Charstrings. This package provides the low-level mechanisms needed to read such formats; the data is consumed in higher level packages, which implement `PsOperatorHandler`. It also provides helpers to interpret glyph outline descriptions, shared between Type1 and CFF font formats.

See https://adobe-type-tools.github.io/font-tech-notes/pdfs/5177.Type2.pdf

Index

Variables 

var (

	// ErrInterrupt signals the interpreter to stop early, without erroring.
	ErrInterrupt = errors.New("interruption")
)

Functions

func GlobalSubr 

func GlobalSubr(state *Machine) error

GlobalSubr pops the subroutine index and call it

func LocalSubr 

func LocalSubr(state *Machine) error

LocalSubr pops the subroutine index and call it

Types

type ArgStack 

type ArgStack struct {
	Vals [psArgStackSize]float64 // we have to use float64 to properly store floats and int32 values
	// Effecive size currently in use. The first value to
	// pop is at index Top-1
	Top int32
}

func (*ArgStack) Clear 

func (a *ArgStack) Clear()

Clear clears the stack

func (*ArgStack) Pop 

func (a *ArgStack) Pop() float64

Pop returns the top level value and decrease `Top` It will panic if the stack is empty.

func (*ArgStack) PopN 

func (a *ArgStack) PopN(numPop int32) error

PopN check and remove the n top levels entries. Passing a negative `numPop` clears all the stack.

func (*ArgStack) Uint16 

func (a *ArgStack) Uint16() uint16

Uint16 returns the top level value as uint16, without popping the stack.

type CharstringReader 

type CharstringReader struct {
	// Acumulated segments for the glyph outlines
	Segments []ot.Segment
	// Acumulated bounds for the glyph outlines
	Bounds PathBounds

	CurrentPoint Point
	// contains filtered or unexported fields
}

CharstringReader provides implementation of the operators found in a font charstring.

func (*CharstringReader) ClosePath 

func (out *CharstringReader) ClosePath()

ClosePath closes the current contour, adding a segment to the first point if needed.

func (*CharstringReader) Flex 

func (out *CharstringReader) Flex(state *Machine) error

func (*CharstringReader) Flex1 

func (out *CharstringReader) Flex1(state *Machine) error

func (*CharstringReader) Hflex 

func (out *CharstringReader) Hflex(state *Machine) error

func (*CharstringReader) Hflex1 

func (out *CharstringReader) Hflex1(state *Machine) error

func (*CharstringReader) Hhcurveto 

func (out *CharstringReader) Hhcurveto(state *Machine)

func (*CharstringReader) Hintmask 

func (out *CharstringReader) Hintmask(state *Machine)

func (*CharstringReader) Hlineto 

func (out *CharstringReader) Hlineto(state *Machine)

func (*CharstringReader) Hmoveto 

func (out *CharstringReader) Hmoveto(state *Machine) error

func (*CharstringReader) Hstem 

func (out *CharstringReader) Hstem(state *Machine)

func (*CharstringReader) Hvcurveto 

func (out *CharstringReader) Hvcurveto(state *Machine)

func (*CharstringReader) Rcurveline 

func (out *CharstringReader) Rcurveline(state *Machine) error

func (*CharstringReader) RelativeCurveTo 

func (out *CharstringReader) RelativeCurveTo(arg1, arg2, arg3 Point)

RelativeCurveTo draws a curve with controls points computed from the current point and `arg1`, `arg2`, `arg3`

func (*CharstringReader) Rlinecurve 

func (out *CharstringReader) Rlinecurve(state *Machine) error

func (*CharstringReader) Rlineto 

func (out *CharstringReader) Rlineto(state *Machine)

func (*CharstringReader) Rmoveto 

func (out *CharstringReader) Rmoveto(state *Machine) error

func (*CharstringReader) Rrcurveto 

func (out *CharstringReader) Rrcurveto(state *Machine)

func (*CharstringReader) Vhcurveto 

func (out *CharstringReader) Vhcurveto(state *Machine)

func (*CharstringReader) Vlineto 

func (out *CharstringReader) Vlineto(state *Machine)

func (*CharstringReader) Vmoveto 

func (out *CharstringReader) Vmoveto(state *Machine) error

func (*CharstringReader) Vstem 

func (out *CharstringReader) Vstem(state *Machine)

func (*CharstringReader) Vvcurveto 

func (out *CharstringReader) Vvcurveto(state *Machine)

type Context 

type Context uint32

Context is the flavour of the Postcript language. 

const (
	TopDict         Context = iota // Top dict in CFF files
	PrivateDict                    // Private dict in CFF files
	Type2Charstring                // Charstring in CFF files
	Type1Charstring                // Charstring in Type1 font files
)

type Machine 

type Machine struct {
	ArgStack ArgStack
	// contains filtered or unexported fields
}

Machine is a PostScript interpreter. A same interpreter may be re-used using muliples `Run` calls.

func (*Machine) CallSubroutine 

func (p *Machine) CallSubroutine(index int32, isLocal bool) error

CallSubroutine calls the subroutine, identified by its index, as found in the instructions (that is, before applying the subroutine biased). `isLocal` controls whether the local or global subroutines are used. No argument stack modification is performed.

func (*Machine) Return 

func (p *Machine) Return() error

Return returns from a subroutine call.

func (*Machine) Run 

func (p *Machine) Run(instructions []byte, localSubrs, globalSubrs [][]byte, handler OperatorHandler) error

Run runs the instructions in the PostScript context asked by `handler`. `localSubrs` and `globalSubrs` contains the subroutines that may be called in the instructions.

func (*Machine) SkipBytes 

func (p *Machine) SkipBytes(count int32)

SkipBytes skips the next `count` bytes from the instructions, and clears the argument stack. It does nothing if `count` exceed the length of the instructions.

type Operator 

type Operator struct {
	Operator  byte
	IsEscaped bool
}

Operator is a postcript command, which may be escaped.

func (Operator) String 

func (p Operator) String() string

type OperatorHandler 

type OperatorHandler interface {
	// Context defines the precise behaviour of the interpreter,
	// which has small nuances depending on the context.
	Context() Context

	// Apply implements the operator defined by `operator` (which is the second byte if `escaped` is true).
	//
	// Returning `ErrInterrupt` stop the parsing of the instructions, without reporting an error.
	// It can be used as an optimization.
	Apply(state *Machine, operator Operator) error
}

OperatorHandler defines the behaviour of an operator.

type PathBounds 

type PathBounds struct {
	Min, Max Point
}

PathBounds represents a control bounds for a glyph outline (in font units).

func (*PathBounds) Enlarge 

func (b *PathBounds) Enlarge(pt Point)

Enlarge enlarges the bounds to include pt

func (*PathBounds) ToExtents 

func (b *PathBounds) ToExtents() ot.GlyphExtents

ToExtents converts a path bounds to the corresponding glyph extents.

type Point 

type Point struct{ X, Y float64 }

Point is a 2D Point in font units.

func (*Point) Move 

func (p *Point) Move(dx, dy float64)

Move translates the Point.

Source Files

charstrings.go interpreter.go

Version
v0.3.0 (latest)
Published
Feb 21, 2025
Platform
linux/amd64
Imports
6 packages
Last checked
14 hours ago –

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