d7fcda345d
- Rename source module from RDReaderView to RDEpubReaderView - Move all source files from Sources/RDReaderView/ to Sources/RDEpubReaderView/ - Update podspec: RDReaderView.podspec -> RDEpubReaderView.podspec - Update Podfile, demo project, and CocoaPods config for new pod name - Delete old RDReaderView pod support files from ReadViewDemo/Pods - Add new RDEpubReaderView pod support files - Update documentation (API ref, architecture, UML, conventions, etc.) - Add FixedLayoutRotationTests - Update .gitignore: exclude .DS_Store, manual unpack backups, _ssoft-output
58 lines
2.2 KiB
Swift
58 lines
2.2 KiB
Swift
import UIKit
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#if canImport(DTCoreText)
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import DTCoreText
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/// Redistributes the leftover space at the bottom of a page into the gaps
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/// between lines so the last line sits flush with the content bottom edge
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/// (vertical justification), keeping page character ranges untouched.
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///
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/// Mutating each line's `baselineOrigin` is sufficient: DTCoreText derives
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/// line frames, glyph-run frames and attachment positions from it lazily,
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/// so drawing, selection, highlights and hit-testing all stay consistent.
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enum RDEPUBTextPageVerticalJustifier {
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/// Leftover larger than this many typical line advances is kept as
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/// whitespace instead of being stretched: it usually comes from a whole
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/// block (image, table) pushed to the next page, and stretching would
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/// make the line spacing visibly sparse.
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static let maxStretchLineAdvanceRatio: CGFloat = 1.5
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static func justify(
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_ layoutFrame: DTCoreTextLayoutFrame,
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contentHeight: CGFloat,
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isChapterLastPage: Bool,
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pixelScale: CGFloat
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) {
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guard !isChapterLastPage,
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contentHeight > 0,
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let lines = layoutFrame.lines as? [DTCoreTextLayoutLine],
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lines.count >= 2,
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let firstLine = lines.first,
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let lastLine = lines.last else {
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return
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}
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let leftover = contentHeight - lastLine.frame.maxY
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guard leftover > 0.5 else { return }
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let gapCount = CGFloat(lines.count - 1)
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let typicalAdvance = (lastLine.baselineOrigin.y - firstLine.baselineOrigin.y) / gapCount
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guard typicalAdvance > 0,
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leftover <= typicalAdvance * maxStretchLineAdvanceRatio else {
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return
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}
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let scale = max(pixelScale, 1)
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for (index, line) in lines.enumerated() where index > 0 {
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// Round each cumulative shift down to the pixel grid so glyphs
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// stay sharp and the last line never overshoots the bottom edge.
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let shift = floor(leftover * CGFloat(index) / gapCount * scale) / scale
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var origin = line.baselineOrigin
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origin.y += shift
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line.baselineOrigin = origin
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}
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}
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}
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#endif
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