Introduction

tfm tfm-validate

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Conclusion

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X Font Metrics Validation: Application to T

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e TUG 2024 E

Didier Verna

EPITA / LRE

didier@lrde.epita.fr

lrde/~didier

@didierverna

didier.verna

in/didierverna

Introduction

tfm tfm-validate

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TFM font validator for T

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Updated daily

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Currently nding 770 fonts with oddities w.r.t. the standard

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Introduction

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Conclusion

The tfm Library

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Part of ETAP

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Bring T

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X Font Metrics information to Common Lisp

Entry Point

CL-USER> (tfm:load-font ".../cmr10.tfm")

#<TFM:FONT cmr10>

CL-USER>

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Design goals: robustness & exibility

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Robustness

Anticipate all potential problems to avoid crashes or erratic behavior.

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20 potential problems identied, various degrees of severity

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Examples

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📕

Truncated le / invalid section pointers → hopeless

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📙

Cycle in a ligature program → some hope

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📗

Comment string inconsistency → benign

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Context-dependent severity

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E.g. (overridden) design size

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Flexibility

When possible, provide recovery options instead of just giving up.

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Currently a dozen

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Examples

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Discarding a bogus kerning / ligature program

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Fixing <table>[0] entries (widths, heights, depths, italic corrections)

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…

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Note: recovery is black magic (we can’t be sure to x the real problem)

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Still, handy in interactive use

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The whole point of tfm: no decision, only options

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Interactive Use vs. Production

Example

CL-USER> (tfm:load-font "/tmp/cmr10.tfm")

While reading /tmp/cmr10.tfm,

while reading the character encoding scheme string,

padded string "TeX (ex)" is not in BCPL format.

See §10 of the TFtoPL documentation for more information.

[Condition of type NET.DIDIERVERNA.TFM:INVALID-PADDED-STRING]

Restarts:

0: [KEEP-STRING] Keep it anyway.

1: [FIX-STRING] Fix it using /'s and ?'s.

2: [DISCARD-STRING] Discard it.

3: [CANCEL-LOADING] Cancel loading this font.

--more--

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Introduction

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tfm’s Error Ontology

For the fun of it…

file-overflow

cancel-loading

padded-string-overflow

invalid-original-design-size

character-list-cycle

discard-next-character

file-underflow

u16-overflow

fix-word-overflow

set-to-zero

invalid-padded-string keep-string

spurious-char-info

invalid-character-code

discard-extension-recipe

discard-kerning

discard-ligature

invalid-character-range

invalid-design-size set-to-ten

invalid-header-length

invalid-ligature-opcode

invalid-section-lengths

invalid-padded-string-length read-maximum-length

invalid-table-index

abort-lig/kern-program

invalid-table-length

invalid-table-start

ligature-cycle

no-boundary-character

fix-string discard-string

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Introduction

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The tfm-validate Library

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Motivation

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Curiosity rather than necessity

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Easy to do

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Key ingredient: the Common Lisp “condition system”

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Exception Handling

func1()

try/catch 1

func2()

try/catch 2

func3()

func4()

throw

func1()

handler 1

func2()

handler 2

restart 1

func3()

restart 2

func4()

signal

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Classic try/catch/throw

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2D SoC: handlers catch & resume

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Common Lisp condition system

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3D SoC: signal / handle / restart

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OO exception management

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Hierarchy of conditions classes

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First-class conditions (instances)

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Application: tfm-validate

(invalidate-font)

tfm handler

(load-font)

cancel loading

(other-func)

other restart

(other-func)

other restart

signal

tfm

tfm-validate

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Just a (big) handler around tfm:load-font

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Entry point: invalidate-font

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Catch all tfm conditions

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Select the “softest” restart

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Collect the conditons before restarting

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Return them at the end

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Convenience 1: invalidate-directory

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Surprisingly high number of issues

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Convenience 2: invalidate-texlive

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Issues in human-readable form (website)

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Current state

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79016 fonts inspected

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2983 fonts skipped (OFM & JFM)

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770 fonts with non compliance issues

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But…

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Only 4 dierent issues found

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3 warnings, 1 error

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Warning: File Overow

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Actual size > declared size

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628 fonts aected

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Only a warning

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The fonts seem functional

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tftopl ignores the junk

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The junk doesn’t seem meaningful

Padding?

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Warning: Padded String Overow

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BCPL string tail 6= 0

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74 fonts aected

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Only a warning

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pltotf ≥ 1.3

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Strings purely informational

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The junk can be meaningful

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Warning: Spurious Char Info

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Absent character 6= 0

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66 fonts aected

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Only a warning

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pltotf zeroes out those chars

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tftopl ignores them

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Obscure matter

Apparently not related to boundary chars

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Error: Fix Word Overow

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Numerical value outside ]-16,+16[

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2 fonts aected

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Error

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Character metrics messed up

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Conclusion

(Real) Conclusion

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Wrap Up

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Motivation: curiosity rather than necessity

Incentive to x (?), monitor new additions

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One merit: the shape of TFM compliance today

Many non-compliant fonts, but only 2 really unusable

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Perspectives

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Support OFM & JFM

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Support other formats (Open Type)

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Improve layout (indexes, cross-references, etc.)

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Add a write-font function to tfm

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X Live / TUG 2024 17/17