THotPDF GPOS Kerning and Placement Methods

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記錄 HotPDF 的 GPOS pair-kerning、contextual kerning、vertical kerning、cursive-anchor、mark-positioning 與 mark-to-ligature queries，以及 text output 期間套用它們的 ShapingFeatures flags

THotPDF API reference

THotPDF Methods Auto Shaping GSUB

說明 HotPDF 的 GPOS pair-kerning、contextual kerning、vertical kerning、cursive-anchor、mark-positioning 與 mark-to-ligature queries，以及文字輸出期間套用它們的 ShapingFeatures flags

Delphi 語法

function HasGPOSKerning: Boolean;

function GetGPOSPairAdjustment(FirstGID, SecondGID: Word): Integer;

function GetGPOSPairAdjustment(FirstGID, SecondGID: Word; out AXPlacement, AYPlacement, AYAdvance: Integer): Integer;

function GetGPOSContextualKernRun(const GIDs: array of Word): TArray<Integer>;

function HasGPOSVerticalKern: Boolean;

function GetGPOSVerticalKern(FirstGID, SecondGID: Word): Integer;

function GetGPOSMarkOffset(BaseGID, MarkGID: Word; out DX, DY: Integer): Boolean;

function GetGPOSMarkMarkOffset(BaseMarkGID, AttachMarkGID: Word; out DX, DY: Integer): Boolean;

function HasGPOSCursive: Boolean;

function GetGPOSCursiveAnchors(GID: Word; out EntryX, EntryY, ExitX, ExitY: Integer; out HasEntry, HasExit: Boolean): Boolean;

function GetGPOSMarkToLigatureOffset(LigGID: Word; ComponentIndex: Integer; MarkGID: Word; out DX, DY: Integer): Boolean;

function GetGPOSLigatureComponentCount(LigGID: Word): Integer;

function ApplyMarkToLigatureShaping(const Wide: UnicodeString): UnicodeString;

Covered APIs

API	使用注意事項
`HasGPOSKerning`	Reports whether the registered Unicode font exposes GPOS kerning lookups
`GetGPOSPairAdjustment`	Returns the signed advance adjustment for an ordered glyph pair and can also return placement-aware X/Y offsets through the overload
`GetGPOSContextualKernRun`	Returns per-glyph contextual kern adjustments by resolving GPOS Type 7 and Type 8 positioning rules over a glyph run
`HasGPOSVerticalKern`	Reports whether the registered Unicode font exposes vertical kerning or vertical proportional adjustment lookups
`GetGPOSVerticalKern`	Returns signed vertical YAdvance adjustment from vkrn or vpal lookups for an ordered glyph pair
`GetGPOSMarkOffset`	Returns Mark-to-Base placement offsets for attaching a mark glyph to a base glyph
`GetGPOSMarkMarkOffset`	Returns Mark-to-Mark placement offsets for stacking one mark glyph on another
`HasGPOSCursive`	Reports whether the registered Unicode font exposes GPOS cursive attachment lookups
`GetGPOSCursiveAnchors`	Returns entry and exit cursive anchors for a glyph when the font supplies a cursive attachment rule
`GetGPOSMarkToLigatureOffset`	Returns Mark-to-Ligature placement offsets for attaching a mark to a specific ligature component
`GetGPOSLigatureComponentCount`	Returns the number of mark-attachment components recorded for a ligature glyph so callers can choose a valid `ComponentIndex` before calling `GetGPOSMarkToLigatureOffset`
`ApplyMarkToLigatureShaping`	Records ligature component ownership so mark-to-ligature offsets can be applied during text emission
`sfKerning`	Enables GPOS pair-kerning adjustments during left-to-right Unicode text emission
`sfMarkPositioning`	Enables GPOS Mark-to-Base and Mark-to-Mark offsets for combining marks
`sfMarkToLigature`	Enables GPOS Mark-to-Ligature offsets for marks attached to individual ligature components
`sfCursiveAttachment`	Enables GPOS cursive entry/exit anchor alignment during Unicode text emission, including right-to-left Arabic runs shaped by `sfArabicGSUB`
`sfVerticalKerning`	Enables GPOS vkrn and vpal vertical advance adjustment in the vertical text output path

使用注意事項

Pair kerning 會以 1000-unit em 傳回 signed advance 與 placement adjustments。Contextual kerning 會跨 glyph run 解析 Type 7 與 Type 8 lookups。Mark positioning 涵蓋 Mark-to-Base、Mark-to-Mark 與 Mark-to-Ligature anchors。ApplyMarkToLigatureShaping 會準備 sfMarkToLigature 使用的 run-level ligature component data。Cursive attachment 會將一個 glyph 的 exit anchor 對齊到下一個 glyph 的 entry anchor，這在 native Arabic GSUB shaping 已產生帶有這些 anchors 的 font-specific contextual glyph IDs 後最有用。emit path 只會在相符 shaping flag 啟用時套用這些項目

請參閱： ShapingFeatures OpenType GSUB Engine Automatic Shaping Pipeline