Read the text-decoration longhands and text-align start, end and match-parent (#607)

[gravitypdf-bot]

Part of #607
Part of #552, part of #520

Problem

mPDF read only the lines of text-decoration, matching underline, overline and line-through inside it by substring. So the longhands, the style, colour and thickness parts of the shorthand, text-underline-offset and text-underline-position were all ignored, and every decoration was drawn as a solid line in the text colour. text-align: start and end, which Bootstrap 5 uses for .text-start and .text-end, and match-parent matched none of the keywords setCSS() or Tag::ALIGN knew.

$mpdf = new \Mpdf\Mpdf();
$mpdf->WriteHTML('<p style="text-decoration: underline wavy #f00">Wavy</p>
<div style="width: 100mm; text-align: end">End</div>
<table style="width: 100mm"><tr><td style="text-align: end">Cell</td></tr></table>');
$mpdf->Output('', 'S');

Rule	Browser	Before	After
p { text-decoration-line: underline }	underlined	no line	underlined
p { text-decoration: underline wavy #f00 }	red wavy underline	straight underline in the text colour	red wavy underline
text-decoration: underline double / dotted / dashed	that style	solid	that style
text-decoration-thickness: 2pt	2pt line	the font's thickness	2pt line
text-underline-offset: 6pt	6pt below the baseline	the font's position	6pt below the baseline
text-underline-position: under	below the descenders	the font's position	below the descenders
div { width: 100mm; text-align: end }	right-aligned	left-aligned	right-aligned
div { width: 100mm; direction: rtl; text-align: end }	left-aligned	right-aligned	left-aligned
td { text-align: end }	right-aligned	left-aligned	right-aligned
<div style="text-align: end"><p dir=rtl style="text-align: match-parent">	right-aligned	right (rtl default)	right-aligned

Fix

Everything here is gated on CssMode::STANDARD.

Decorations

• NormalizeProperties expands the text-decoration shorthand: the line keywords stay in TEXT-DECORATION, so the propagation from Draw an ancestor's text decorations over its descendants instead of letting them inherit or undo them #654 and everything else that reads it is unchanged. The style, colour (currentcolor by default) and thickness go to their longhands, each reset to its initial value where the shorthand leaves it out. text-decoration-line is read as TEXT-DECORATION. A CSS-wide keyword on the shorthand reaches each longhand. CssWideKeywords knows the new initial values.
• setCSS() adds the element's style, decoration colour, thickness, underline offset and under position to the text parameter of each line the element sets itself (Mpdf::decorationDrawing()). Because Draw an ancestor's text decorations over its descendants instead of letting them inherit or undo them #654 copies those parameters to descendants, a propagated line keeps its own style and colour. An element's own decoration drops the keys of the one it replaces, so <span style="text-decoration: underline"> inside a wavy paragraph draws a solid line.
• The drawing code takes the thickness from the parameter, and for the underline places its top at the offset below the baseline, or below the font's descent for under. TextDecorations::stroke() draws solid, double (two lines a thickness apart, the second away from the text; either side of the line for line-through), dotted (round dots), dashed, and wavy (whole half waves of a sine, each one cubic Bézier, fitted to the text width).
• text-underline-offset and text-underline-position are inherited (InheritedProperties::DECORATION) and read where the underline is set, so p { text-underline-offset: 2mm } moves the underline of a link inside it. A length in em is taken of the element that declares it, like other inherited lengths.

Alignment

• start and end map to left or right against the block's direction after setCSS() has read it, and against the cell's direction in Td.
• match-parent is resolved in ComputedValues: it computes to the parent's alignment, with the parent's start or end taken against the parent's direction, so its children inherit the resolved value.

Decisions

• Offset. A length offset is from the alphabetic baseline to the top of the line, as Chrome and Firefox draw it, so text-underline-offset: 0 puts the line at the baseline. auto keeps the font's position.
• Thickness. auto and from-font both take the font's post underline thickness, which is what mPDF already drew. A percentage is of 1em.
• text-underline-position: left / right are for vertical text, which mPDF does not set, so they are read as auto.
• Wavy proportions. Crest to trough is three thicknesses and a half wave three thicknesses long, near what browsers draw.

Legacy mode

Unchanged. The shorthand is not expanded, the longhands are not read, and start, end and match-parent are ignored, as before. Solid lines are drawn through the same operators as before, and no existing snapshot fixture changed. Nothing here only fixes a crash, so nothing applies in both modes.

Not in this PR

• word-break, overflow-wrap and word-wrap. They touch WriteFlowingBlock() and the table column minimum widths, which other PRs are working on at the same time (Align inline text with vertical-align keywords, and indent cells and hanging lines with text-indent #608). They are the third part of Read the text-decoration longhands, text-align: start and end, and word-break and overflow-wrap #607 and can follow as their own PR.
• start and end in the text-align of form fields (input, textarea) and of hr. Those read Tag::getAlign(), which still does not know them.

Tests

• tests/Mpdf/TextDecorationLonghandsTest.php: the line longhand; the shorthand's parts in any order; legacy drawing a plain line in the text colour; the shorthand and longhands cascading both ways; the colour on a nested span and on a propagated line; an own decoration not keeping the style it replaces; the operators each of the five styles writes; double-line spacing for underline and line-through; a wavy line spanning the text and alternating; thickness as a length, a percentage and on line-through/overline, with auto/from-font unchanged; the offset from the baseline in pt and em; under below the descenders with an offset from there, using a font with descenders; inheritance of the offset to an inline element, a child block and a cell; CSS-wide keywords on the longhands; legacy ignoring all of it byte for byte.
• tests/Mpdf/TextAlignLogicalTest.php: start/end in ltr and rtl blocks and cells against their physical equivalents, end inherited into an rtl child, match-parent against the parent's end and rtl start, a physical parent value, its resolved value handed on, a cell's match-parent from its row, a cell inheriting end from its table, and legacy ignoring them.
• Snapshot text-decoration-align: each style and colour, thickness, the font's underline position beside text-underline-offset: 0, 6pt and text-underline-position: under, then start/end in ltr and rtl blocks, match-parent, and end in ltr and rtl cells, each under a caption saying what it should show. I rasterised it and checked each case against its caption. Against the pre-fix src/ it fails (page 1 RMSE 0.039).

Checks

• composer test: OK, 12771 tests, 31 skipped (none of them snapshots)
• composer cs: clean
• PHPStan 2 (--memory-limit=2G): 23 errors, all pre-existing on gravitypdf (Regenerate the PHPStan baseline for PHPStan 2.3, so the Lint job passes again #716 regenerates the baseline); none in the changed files

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