Reimplement adaptive encoding

[dennwc]

Reimplement adaptive encoding removed in previous commits related to encoding.

This function still uses an old approach - the whole alphabet should be given upfront to create an encoding. The next change will introduce an incremental encoder.

[codecov]

Codecov Report

Merging #326 into v3 will increase coverage by 5.54%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##               v3     #326      +/-   ##
==========================================
+ Coverage   52.61%   58.16%   +5.54%     
==========================================
  Files         145      145              
  Lines       25236    25275      +39     
==========================================
+ Hits        13278    14701    +1423     
- Misses      10170    10209      +39     
+ Partials     1788      365    -1423

Impacted Files	Coverage Δ
pdf/model/font.go	61.57% <0%> (+2.44%)	⬆️
pdf/creator/division.go	89.13% <0%> (+1.08%)	⬆️
pdf/model/outline.go	86.74% <0%> (+1.2%)	⬆️
pdf/creator/invoice.go	90.07% <0%> (+1.21%)	⬆️
pdf/model/annotations.go	22.56% <0%> (+1.48%)	⬆️
pdf/creator/toc_line.go	75.39% <0%> (+1.58%)	⬆️
pdf/internal/transform/matrix.go	67.27% <0%> (+1.81%)	⬆️
pdf/internal/textencoding/truetype.go	16% <0%> (+2%)	⬆️
pdf/creator/chapters.go	64.94% <0%> (+2.06%)	⬆️
pdf/model/fonts/std.go	90% <0%> (+2.5%)	⬆️
... and 88 more

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[gunnsth]

@dennwc Would it be worth making a test case for NewStandard14FontWithEncoding ?
Are you planning to keep it when the adaptive/incremental encoding is introduced?

[dennwc]

@gunnsth Incremental encoding will make this function useless, I guess. I consider this a "backup plan" for incremental encoding. If a good implementation of incremental encoding will take too much time or will require significant changes, this PR will at least cover the feature until it's done.

[gunnsth-review]

Reviewable status: 0 of 1 files reviewed, 2 unresolved discussions (waiting on @dennwc)

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pdf/model/font.go, line 132 at r1 (raw file):

// a TextEncoder that encodes all the runes in `alphabet`, or an error if this is not possible.
// An error can occur if `basefont` is not one the standard 14 font names.
func NewStandard14FontWithEncoding(basefont fonts.StdFontName, alphabet map[rune]int) (*PdfFont,

Is there any way to test this? E.g. given the inputalphabet, check that the encoder behaves correctly?

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pdf/model/font.go, line 214 at r1 (raw file):

// GetAlphabet returns a map of the runes in `text` and their frequencies.
func GetAlphabet(text string) map[rune]int {

Add a couple of basic tests, check map output of a few input strings with 0, 1, multiple instances of runes.