THotPDF GPOS Kerning and Placement Methods

THotPDF API reference

Documents HotPDF's GPOS pair-kerning, contextual kerning, vertical kerning, cursive-anchor, mark-positioning, and mark-to-ligature queries plus the ShapingFeatures flags that apply them during text output

function ApplyMarkToLigatureShaping(const Wide: UnicodeString): UnicodeString;

Delphi syntax

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;

Covered APIs

API	Usage notes
`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
`ApplyMarkToLigatureShaping`	Records ligature component data for mark-to-ligature placement
`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
`sfVerticalKerning`	Enables GPOS vkrn and vpal vertical advance adjustment in the vertical text output path

Usage notes

Pair kerning returns signed advance and placement adjustments in a 1000-unit em. Contextual kerning resolves Type 7 and Type 8 lookups across a glyph run. Mark positioning covers Mark-to-Base, Mark-to-Mark, and Mark-to-Ligature anchors. The emit path applies these only when sfKerning, sfMarkPositioning, or sfVerticalKerning is enabled