THotPDF GPOS Kerning and Placement Methods

Referenčné API THotPDF

Dokumentuje dotazy GPOS pre párové kerningové úpravy, kontextové kerningové úpravy, vertikálne kerningové úpravy, kurzívne kotvy, umiestňovanie značiek a mark-to-ligature spolu s príznakmi ShapingFeatures, ktoré ich aplikujú pri výstupe textu

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;

function GetGPOSLigatureComponentCount(LigGID: Word): Integer;

function ApplyMarkToLigatureShaping(const Wide: UnicodeString): UnicodeString;

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
`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

Usage notes

Párové kerningové úpravy vracajú podpísané zmeny prírastku a umiestnenia v 1000-účtovom em. Kontextové kerningové úpravy riešia vyhľadávania typu 7 a typu 8 naprieč tokom glyfov. Umiestňovanie značiek pokrýva kotvy Mark-to-Base, Mark-to-Mark a Mark-to-Ligature. ApplyMarkToLigatureShaping pripraví údaje o komponentoch ligatúr na úrovni toku, ktoré používa sfMarkToLigature. Kurzívne pripojenie zarovná výstupnú kotvu jedného glyfu na vstupnú kotvu nasledujúceho glyfu, čo je najužitočnejšie po tom, čo natívne arabské tvarovanie GSUB vytvorí fontovo špecifické kontextové ID glyfov, ktoré tieto kotvy nesú. Výstupná cesta ich aplikuje len vtedy, keď je zapnutý zodpovedajúci tvarovací príznak