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InstantPage V2: text items measure true font height (A + D)

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Shift the line stack down by the ascender headroom (A - L, as
`lineBoxTopInset` to avoid colliding with the existing formula-bleed
`topInset` local) and pad the returned height by the last line's
descender (D), so a single-line V2 text item is a true ascent/descent
line box measuring exactly A + D instead of the cap box A - L. Inter-line
advance unchanged; formulas still inflate via lineAscent/extraDescent.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
isaac 2026-06-01 02:20:10 +02:00
parent 758e596bf9
commit 18d124ab17
1 changed files with 12 additions and 2 deletions
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14
submodules/InstantPageUI/Sources/InstantPageV2Layout.swift
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@ -2754,10 +2754,18 @@ func layoutTextItem(
let fontLineHeight = floor(fontAscent + fontDescent)
let fontLineSpacing = floor(fontLineHeight * lineSpacingFactor)
let fontDescentBelowBaseline = max(0.0, -fontDescent)
// True font-height line box: shift the whole line stack down by the ascender headroom above
// the cap line (A − L) and pad the final height by the descender (D) below the last baseline,
// so a single-line item measures exactly A + D. Exact (not pixel-snapped): this is an
// intra-item line offset; crispness rides on the item's own pixel-snapped frame origin, and
// intra-item line positions may already be fractional (e.g. after a non-integral extraDescent).
// Inter-line advance is unchanged. (Named `lineBoxTopInset` to avoid colliding with the
// formula-bleed `topInset` local near the end of this function.)
let lineBoxTopInset = max(0.0, fontAscent - fontLineHeight)
let baselineToNextTopSlack = max(0.0, fontLineSpacing - 4.0)
var lastIndex: CFIndex = 0
var currentLineOrigin = CGPoint()
var currentLineOrigin = CGPoint(x: 0.0, y: lineBoxTopInset)
var hasAnchors = false
var maxLineWidth: CGFloat = 0.0
@ -3097,7 +3105,9 @@ func layoutTextItem(
var height: CGFloat = 0.0
if !lines.isEmpty && !(string.string == "\u{200b}" && hasAnchors) {
height = lines.last!.frame.maxY + extraDescent
// + fontDescentBelowBaseline: contain the last line's descender below its baseline, so
// (with the topInset shift) a single-line item measures exactly A + D = true font height.
height = lines.last!.frame.maxY + extraDescent + fontDescentBelowBaseline
}
var textWidth = boundingWidth