Class: Fontisan::Hints::TrueTypeInstructionGenerator

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/hints/truetype_instruction_generator.rb

Overview

Generates TrueType instruction bytecode from PostScript hint parameters

This class is the inverse of TrueTypeInstructionAnalyzer - it takes PostScript hint parameters and generates equivalent TrueType prep/fpgm programs and CVT values.

TrueType Instruction Opcodes:

  • NPUSHB (0x40): Push n bytes

  • NPUSHW (0x41): Push n words (16-bit)

  • PUSHB (0xB0-0xB7): Push 1-8 bytes

  • PUSHW (0xB8-0xBF): Push 1-8 words

  • SSW (0x1F): Set Single Width

  • SSWCI (0x1E): Set Single Width Cut-In

  • SCVTCI (0x1D): Set CVT Cut-In

  • WCVTP (0x44): Write CVT in Pixels

  • WCVTF (0x70): Write CVT in FUnits

Examples:

Generate TrueType programs

generator = TrueTypeInstructionGenerator.new
programs = generator.generate({
  blue_scale: 0.039625,
  std_hw: 80,
  std_vw: 90
})
programs[:prep] # => Binary prep program
programs[:fpgm] # => Binary fpgm program (usually empty)
programs[:cvt]  # => Array of CVT values

Constant Summary collapse

NPUSHB =

TrueType instruction opcodes

0x40
NPUSHW =

Push n bytes

0x41
PUSHB_BASE =

Push n words (16-bit)

0xB0
PUSHW_BASE =

PUSHB through PUSHB

0xB8
SSW =

PUSHW through PUSHW

0x1F
SSWCI =

Set Single Width

0x1E
SCVTCI =

Set Single Width Cut-In

0x1D
WCVTP =

Set CVT Cut-In

0x44
WCVTF =

Write CVT in Pixels

0x70
MAX_PUSHB_INLINE =

Size thresholds for instruction selection

8
MAX_PUSHW_INLINE =

Maximum bytes for PUSHB

8
BYTE_MAX =

Maximum words for PUSHW

255
WORD_MAX =

Maximum value for byte

65535

Instance Method Summary collapse

Instance Method Details

#generate(ps_params) ⇒ Hash

Generate TrueType programs and CVT from PostScript parameters

Parameters:

  • ps_params (Hash) —

    PostScript hint parameters

Options Hash (ps_params):

  • :blue_scale (Float) —

    Blue scale value (0.0-1.0)

  • :std_hw (Integer) —

    Standard horizontal width

  • :std_vw (Integer) —

    Standard vertical width

  • :stem_snap_h (Array<Integer>) —

    Horizontal stem snap values

  • :stem_snap_v (Array<Integer>) —

    Vertical stem snap values

  • :blue_values (Array<Integer>) —

    Blue zone values

  • :other_blues (Array<Integer>) —

    Other blue zone values

Returns:

  • (Hash) —

    Hash with :prep, :fpgm, and :cvt keys



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# File 'lib/fontisan/hints/truetype_instruction_generator.rb', line 61

def generate(ps_params)
  # Normalize keys to symbols
  ps_params = normalize_keys(ps_params)

  {
    fpgm: generate_fpgm(ps_params),
    prep: generate_prep(ps_params),
    cvt: generate_cvt(ps_params)
  }
end

#generate_cvt(ps_params) ⇒ Array<Integer>

Generate CVT (Control Value Table) from PostScript parameters

CVT entries are derived from:

  • stem_snap_h/stem_snap_v: Stem widths

  • blue_values/other_blues: Alignment zones

  • std_hw/std_vw: Standard widths

Duplicates are removed and values sorted for optimal CVT organization.

Parameters:

  • ps_params (Hash) —

    PostScript parameters

Returns:

  • (Array<Integer>) —

    Array of 16-bit signed integers



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# File 'lib/fontisan/hints/truetype_instruction_generator.rb', line 132

def generate_cvt(ps_params)
  cvt = []

  # Add standard widths to CVT
  cvt << ps_params[:std_hw] if ps_params[:std_hw]
  cvt << ps_params[:std_vw] if ps_params[:std_vw]

  # Add stem snap values
  if ps_params[:stem_snap_h]
    cvt.concat(ps_params[:stem_snap_h])
  end

  if ps_params[:stem_snap_v]
    cvt.concat(ps_params[:stem_snap_v])
  end

  # Add blue zone values (as pairs: bottom, top)
  if ps_params[:blue_values]
    cvt.concat(ps_params[:blue_values])
  end

  if ps_params[:other_blues]
    cvt.concat(ps_params[:other_blues])
  end

  # Remove duplicates and sort for optimal CVT organization
  cvt.uniq.sort
end

#generate_fpgm(_ps_params) ⇒ String

Generate fpgm (Font Program) from PostScript parameters

For converted fonts, fpgm is typically empty as font-level functions are not needed for basic hint conversion.

Parameters:

  • _ps_params (Hash) —

    PostScript parameters (unused)

Returns:

  • (String) —

    Binary instruction bytes (empty for converted fonts)



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# File 'lib/fontisan/hints/truetype_instruction_generator.rb', line 115

def generate_fpgm(_ps_params)
  # For converted fonts, fpgm is typically empty
  # Advanced implementations might generate function definitions here
  "".b
end

#generate_prep(ps_params) ⇒ String

Generate prep (Control Value Program) from PostScript parameters

The prep program sets up global hint parameters:

  • CVT Cut-In (from blue_scale)

  • Single Width Cut-In (from std_hw/std_vw)

  • Single Width (from std_hw or std_vw)

Parameters:

  • ps_params (Hash) —

    PostScript parameters

Returns:

  • (String) —

    Binary instruction bytes



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# File 'lib/fontisan/hints/truetype_instruction_generator.rb', line 81

def generate_prep(ps_params)
  instructions = []

  # Set CVT Cut-In from blue_scale if present
  if ps_params[:blue_scale]
    cvt_cut_in = calculate_cvt_cut_in(ps_params[:blue_scale])
    instructions.concat(push_value(cvt_cut_in))
    instructions << SCVTCI
  end

  # Set Single Width Cut-In if we have stem widths
  if ps_params[:std_hw] || ps_params[:std_vw]
    sw_cut_in = calculate_sw_cut_in(ps_params)
    instructions.concat(push_value(sw_cut_in))
    instructions << SSWCI
  end

  # Set Single Width (prefer horizontal, fall back to vertical)
  single_width = ps_params[:std_hw] || ps_params[:std_vw]
  if single_width
    instructions.concat(push_value(single_width))
    instructions << SSW
  end

  instructions.pack("C*")
end