Skip to content

fix(preview): stop shrinking text in shapes without normAutofit #293

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
baseballyama merged 1 commit into from
Jul 31, 2026
Merged

fix(preview): stop shrinking text in shapes without normAutofit #293

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
15 changes: 15 additions & 0 deletions .changeset/heavy-buses-tell.md
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
---
'@office-kit/pptx-preview': patch
---

fix(preview): stop shrinking text in shapes without `<a:normAutofit>`

PowerPoint never shrinks text in shapes that lack `<a:normAutofit>`:
`<a:noAutofit>` (or no autofit element) simply overflows the box, and
`<a:spAutoFit>` grows the box to fit the text. The preview applied a
heuristic shrink-to-fit to such shapes, which rendered template
placeholders (font size inherited from the layout/master, box authored
tightly around the sample text) at down to 0.4× of their PowerPoint
size. The heuristic estimator is removed; only an authored
`<a:normAutofit>` (with or without a baked `fontScale`) shrinks text,
matching PowerPoint.
59 changes: 9 additions & 50 deletions packages/preview/src/render-slide.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2147,13 +2147,6 @@ const renderRun = (
// `line-height` declaration in renderRun.
const LINE_HEIGHT = 1.05;

// Rough mean glyph width as a fraction of font-size in a typical
// sans-serif. 0.55 is what PowerPoint's auto-fit estimator uses for
// Calibri at body sizes. Used to estimate when text wraps so the
// renderer can shrink the font to keep wrapped placeholders from
// overflowing.
const AVG_GLYPH_W_RATIO = 0.55;

// `<a:normAutofit/>` shrink-to-fit search bounds. PowerPoint reduces the font
// in discrete steps until the body fits its box; we sweep from 1.0 down to the
// floor in fixed decrements. The floor stops a pathologically small box from
Expand Down Expand Up @@ -2754,51 +2747,17 @@ export const resolveTextBodyModel = (
// computed one (`<a:normAutofit fontScale=…/>`). That's the same
// multiplier PowerPoint applies on-screen, so honouring it is what
// brings the rendered size into 1:1 agreement with the deck.
//
// No estimation happens for shapes WITHOUT `<a:normAutofit>`: PowerPoint
// never shrinks those — `<a:noAutofit>` (and no autofit at all) simply
// overflows the box, and `<a:spAutoFit>` grows the box instead of the text.
// An earlier heuristic shrank such shapes to fit their authored box, which
// rendered template placeholders (size inherited from layout/master, box
// sized by the template author) at up to 0.4× of their PowerPoint size.
const authoredAutofit = getShapeTextAutoFitParams(shape);
let autoFitScale = authoredAutofit?.fontScale ?? 1;
let lineHeightScale = 1 - (authoredAutofit?.lnSpcReduction ?? 0);

// Only fall back to the heuristic estimator when no authored
// autofit ran. CJK glyphs are ~1em wide vs the ~0.55em Latin
// average, so detect a leading CJK character per paragraph and
// widen the per-line estimate accordingly — keeps Japanese titles
// from over-shrinking on placeholders that already fit.
if (!authoredAutofit) {
const innerWPx = innerW / EMU_PER_PX;
const innerHPx = innerH / EMU_PER_PX;
let totalH = 0;
for (const para of paraData) {
let maxSize = defaultPt;
let totalChars = 0;
let cjkChars = 0;
for (const run of para.runs) {
if (run.sizePt > maxSize) maxSize = run.sizePt;
totalChars += run.text.length;
for (let i = 0; i < run.text.length; i++) {
const c = run.text.charCodeAt(i);
// CJK Unified Ideographs, Hiragana, Katakana, Hangul.
if (
(c >= 0x3040 && c <= 0x309f) ||
(c >= 0x30a0 && c <= 0x30ff) ||
(c >= 0x4e00 && c <= 0x9fff) ||
(c >= 0xac00 && c <= 0xd7af)
)
cjkChars++;
}
}
if (totalChars === 0) totalChars = 1;
const cjkRatio = cjkChars / totalChars;
// Weighted average: CJK glyphs ≈ 1.0em wide, Latin ≈ 0.55em.
const glyphRatio = cjkRatio * 1.0 + (1 - cjkRatio) * AVG_GLYPH_W_RATIO;
const sizePx = maxSize * PX_PER_PT;
const charsPerLine = Math.max(1, Math.floor(innerWPx / Math.max(1, sizePx * glyphRatio)));
const lineCount = Math.max(1, Math.ceil(totalChars / charsPerLine));
totalH += sizePx * LINE_HEIGHT * lineCount;
}
if (totalH > innerHPx) {
autoFitScale = Math.max(0.4, innerHPx / totalH);
}
}
const lineHeightScale = 1 - (authoredAutofit?.lnSpcReduction ?? 0);

// Apply line-height reduction by tightening per-line spacing. We
// pass it through to renderRun via a closed-over factor.
const effectiveLineHeight = LINE_HEIGHT * lineHeightScale;
Expand Down
Loading