Creating text nodes

What are nodes?

Text data structure

Hierarchical structure

func NewText() *Text

type Text struct {
	Settings TypesettingSettings
	Items    []any
}

Text can be a nested structure. Think of

<em>this is <u>emphasized and underlined</u></em>

where you can consider the underlined part as a child of the emphasized part.

ul := NewText()
ul.Settings[]
ul.Items = append(ul.Items,"emphasized and underlined")

em := NewText()
em.Settings...
em.Items = append(em.Items, "this is ")
em.Items = append(em.Items, ul

Format a paragraph

font family needed

This breaks a paragraph into lines:

func (fe *Document) FormatParagraph(te *Text, hsize bag.ScaledPoint, opts ...TypesettingOption) (*node.VList, *ParagraphInfo, error)

hsize is the desired horizontal size.

format paragraph calls mknodes

func (fe *Document) Mknodes(ts *Text) (head node.Node, tail node.Node, err error)

which creates a list of nodes from a nested Text data structure.

Typesetting options

The FormatParagraph() method takes a typesetting options as the last argument.

type TypesettingOption func(*Options)

Option	Description
`Leading(leading bag.ScaledPoint)`	Set the vertical distance between two baselines
`Language(language *lang.Lang)`	Set the language used for hyphenation
`FontSize(size bag.ScaledPoint)`	Set the font size for the paragraph
`IndentLeft(size bag.ScaledPoint, rows int)`	Set the text indent
`HorizontalAlign(a HorizontalAlignment)`	Sets the horizontal alignment for a paragraph

Text settings

Settings on a Text object control how its content is converted to nodes by Mknodes.

Setting	Type	Description
`SettingFontFamily`	`*FontFamily`	The font family to use
`SettingSize`	`bag.ScaledPoint`	Font size
`SettingColor`	`*color.Color`	Text color
`SettingLeading`	`bag.ScaledPoint`	Line height (baseline to baseline)
`SettingHAlign`	`HorizontalAlignment`	Horizontal alignment
`SettingIndentLeft`	`bag.ScaledPoint`	Left indentation
`SettingIndentLeftRows`	`int`	Number of rows to indent (0 = all)
`SettingIndentLeftSteps`	`[]node.IndentStep`	Left inset that changes from row to row, in place of the two above (see Linebreaking)
`SettingIndentRightSteps`	`[]node.IndentStep`	The same for the right inset
`SettingLeader`	`string`	Leader pattern string (see below)
`SettingHyperlink`	`document.Hyperlink`	Link target (URI or local destination)
`SettingDest`	`string`	Named PDF destination at the start of the text, a target for internal links
`SettingFontWeight`	`FontWeight` or `int`	Font weight, 100 to 900
`SettingStyle`	`FontStyle`	Upright, italic or oblique
`SettingLanguage`	`*lang.Lang`	Hyphenation language of the text
`SettingOpenTypeFeature`	`string` or `[]string`	OpenType features, such as `"+smcp,-liga"`
`SettingLetterSpacing`	`bag.ScaledPoint`	Extra space after every glyph and every space (CSS `letter-spacing`)
`SettingFontExpansion`	`float64`	How far glyphs may be narrowed or widened to even out the spacing of a justified line, 0.05 is 5%; ragged paragraphs are set without it
`SettingHorizontalScale`	`float64`	Glyphs narrower or wider by a fixed factor, 0.9 is 90%; the line breaker sees the scaled width
`SettingHalfLeading`	`bool`	Leading half above, half below each line, as in CSS; unset puts it below the line, as TeX does
`SettingLineModel`	`node.LineModel`	Line spacing by a model of your own, in place of the two above (see Linebreaking)
`SettingBreaker`	`node.Breaker`	Breaks chosen by a breaker of your own, in place of Knuth-Plass (see Linebreaking)
`SettingRecordLineTrims`	`bool`	Record each line’s trims at the paragraph font’s text edges, for `text-box-trim`
`SettingBackgroundArea`	`BackgroundArea`	The box an inline background covers: `BackgroundAreaEmBox` (default) or `BackgroundAreaAscentDescent`, the content area browsers paint

Leaders via SettingLeader

When a Text item has a SettingLeader value, Mknodes creates a leader glue node instead of normal text. The string value (e.g. ".") is shaped into glyphs, packed into an HList pattern, and attached to a glue node with StretchFilll (order 3). The leader dominates over line-end glue, pushing trailing content to the right margin.

leaderText := frontend.NewText()
leaderText.Settings[frontend.SettingFontFamily] = ff
leaderText.Settings[frontend.SettingSize] = bag.MustSP("10pt")
leaderText.Settings[frontend.SettingLeader] = " . "

pageNum := frontend.NewText()
pageNum.Settings[frontend.SettingFontFamily] = ff
pageNum.Items = append(pageNum.Items, "42")

tocLine := frontend.NewText()
tocLine.Settings[frontend.SettingFontFamily] = ff
tocLine.Items = append(tocLine.Items, "Chapter 1")
tocLine.Items = append(tocLine.Items, leaderText)
tocLine.Items = append(tocLine.Items, pageNum)

vl, _, _ := doc.FormatParagraph(tocLine, hsize,
    frontend.Family(ff),
    frontend.HorizontalAlign(frontend.HAlignLeft))

This produces: Chapter 1 . . . . . . . . . 42 with the dots vertically aligned across lines (global grid).

Mathematics Simple PDF drawing library