Add opt-in synthetic font weight for fonts without bold faces#854
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Currently we're focusing on migrating the toolkit to Swift 6 with strict concurrency support in the |
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Fixes #853.
Problem
EPUBPreferences.fontWeightmaps to a CSSfont-weightoverride injected into the page. WebKit can only apply a heavier weight when the font actually ships a bold face. For single-face fonts — most notably custom fonts declared throughfontFamilyDeclarations— WebKit does not synthesize bolding, sofontWeighthas no visible effect. Rendering the same passage atfontWeight1.0 and 1.5 with a single-face font produces pixel-identical output.This is an engine limitation, so
font-weightalone cannot fix it. We need a separate channel to thicken glyphs.Approach
Add an opt-in
fontWeightSynthesis: BoolEPUB preference, defaulting to off (nil/false). When it is enabled andfontWeightis greater than 1.0,ReadiumCSSemits a-webkit-text-stroke-widthoverride alongside the existingfont-weightentry:Notes on the design:
em-based. The stroke width scales with the font size instead of being a fixed pixel value.-webkit-text-stroke-coloris intentionally left unset; it defaults tocurrentColor, which tracks the text color across the light, dark and sepia themes.<html>and updated live throughreadium.setCSSProperties.-webkit-text-strokeinherits, so applying it on<html>covers all text, and an empty value clears it on live settings changes (mirroring thefont-weightentry). Both call sites handle the new key without changes.The preference is wired through
EPUBPreferences,EPUBSettings,EPUBDefaultsandEPUBPreferencesEditor, following the exact pattern oftextNormalization.Tests
Added
ReadiumCSSTestscases covering theupdate(with:)mapping: synthesis off emits no stroke; on with weight not above 1.0 or unset emits none; on with weight 1.75 gives0.0175em; on with weight 2.5 gives0.0350em; and an out-of-range weight is clamped to the 2.5 result.Verification
xcodebuild test -scheme Readium-Package -destination 'platform=iOS Simulator,name=iPhone 17' -only-testing:ReadiumNavigatorTests— 110 tests pass, including the 5 new cases.swift run --package-path BuildTools swiftformat --lint .— clean.