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Avoid too long BlueScale value when rewriting a CFF font

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It fixes #21466.
This commit is contained in:
calixteman 2026-06-18 18:52:04 +02:00
parent 3956ac1b39
commit 07d4c1018a
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GPG Key ID: 0C5442631EE0691F
2 changed files with 29 additions and 2 deletions
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8
src/core/cff_parser.js
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@ -902,10 +902,14 @@ class CFFParser {
// BlueScale up only misaligns/collapses overshooting glyphs (notably
// with macOS's Core Text rasterizer). Only apply the lower clamp when
// its target does not exceed the default.
// Round the bound in order to avoid too long operand (issue 21466).
const PRECISION = 1e5;
const lowerBound = 0.5 / maxZoneHeight;
const minBlueScale =
lowerBound <= DEFAULT_BLUE_SCALE ? lowerBound : -Infinity;
const maxBlueScale = 1 / maxZoneHeight;
lowerBound <= DEFAULT_BLUE_SCALE
? Math.ceil(lowerBound * PRECISION) / PRECISION
: -Infinity;
const maxBlueScale = Math.floor(PRECISION / maxZoneHeight) / PRECISION;
const clamped = MathClamp(blueScale, minBlueScale, maxBlueScale);
if (clamped !== blueScale) {
privateDict.setByName("BlueScale", clamped);

23
test/unit/cff_parser_spec.js
View File

@ -389,6 +389,29 @@ describe("CFFParser", function () {
);
});
it("clamps BlueScale to a short decimal so the recompiled operand stays compact", function () {
// maxZoneHeight = 13 gives lower bound (0.5 / 13 = 0.038461538461538464)
// which is too long (issue 21466).
cff.topDict.privateDict = new CFFPrivateDict(cff.strings);
cff.topDict.privateDict.setByName(
"BlueValues",
[-13, 13, 530, 13, 220, 13, 30, 13]
);
cff.topDict.privateDict.setByName("BlueScale", 0.01);
cff.topDict.setByName("Private", [0, 0]);
const fontDataShortBlueScale = new CFFCompiler(cff).compile();
const reparsedCff = new CFFParser(
new Stream(fontDataShortBlueScale),
{},
SEAC_ANALYSIS_ENABLED
).parse();
const blueScale = reparsedCff.topDict.privateDict.getByName("BlueScale");
expect(blueScale).toEqual(0.03847);
expect(new CFFCompiler(cff).encodeFloat(blueScale).length).toBeLessThan(6);
});
it("refuses to add topDict key with invalid value (bug 1068432)", function () {
const topDict = cff.topDict;
const defaultValue = topDict.getByName("UnderlinePosition");