When converting C function prototypes to Pascal equivalent declarations, it's important to substitute the C function and argument types with the correct Pascal types. I often use a Type Translation Table for this, like the following in table 1 (optional parts on the C-side are noted between square brackets):

 

C/C++ Type	ObjectPascal Type
unsigned short [int]	Word
[signed] short [int]	SmallInt
unsigned [int]	Cardinal { 3.25 fix }
[signed] int	Integer
UINT	LongInt { or Cardinal }
WORD	Word
DWORD	LongInt { or Cardinal }
unsigned long	LongInt { or Cardinal }
unsigned long int	LongInt { or Cardinal }
[signed] long	LongInt
[signed] long int	LongInt
char	Char
signed char	ShortInt
unsigned char	Byte
char*	PChar
LPSTR or PSTR	PChar
LPWSTR or PWSTR	PWideChar { 3.12 fix }
void*	Pointer
BOOL	Bool
float	Single
double	Double
long double	Extended
LP,NP,PP,P prefix: if first = T then T becomes P else P prefix
HANDLE	THandle
FARPROC	TFarProc
ATOM	TAtom
TPOINT	TPoint
TRECT	TRect
COLORREF	TColorRef
OFSTRUCT	TOFStruct
DEBUGHOOKINFO	TDebugHookInfo
BITMAP	TBitMap
RGBTRIPLE	TRGBTriple
RGBQUAD	TRGBQuad
BITMAPCOREHEADER	TBitmapCoreHeader
BITMAPINFOHEADER	TBitmapInfoHeader
BITMAPINFO	TBitmapInfo
BITMAPCOREINFO	TBitmapCoreInfo
BITMAPFILEHEADER	TBitmapFileHeader
HANDLETABLE	THandleTable
METARECORD	TMetaRecord
METAHEADER	TMetaHeader
METAFILEPICT	TMetaFilePict
TEXTMETRIC	TTextMetric
NEWTEXTMETRIC	TNewTextMetric
LOGBRUSH	TLogBrush
LOGPEN	TLogPen
PATTERN	TPattern { TLogBrush }
PALETTEENTRY	TPaletteEntry
LOGPALETTE	TLogPalette
LOGFONT	TLogFont
ENUMLOGFONT	TEnumLogFont
PANOSE	TPanose
KERNINGPAIR	TKerningPair
OUTLINETEXTMETRIC	TOutlineTextMetric
FIXED	TFixed
MAT2	TMat2
GLYPHMETRICS	TGlyphMetrics
POINTFX	TPointFX
TTPOLYCURVE	TTTPolyCurve
TTPOLYGONHEADER	TPolygonHeader
ABC	TABC
RASTERIZER_STATUS	TRasterizer_Status
MOUSEHOOKSTRUCT	TMouseHookStruct
CBTACTIVATESTRUCT	TCBTActivateStruct
HARDWAREHOOKSTRUCT	THardwareHookStruct
EVENTMSG	TEventMsg
WNDCLASS	TWndClass
MSG	TMsg
MINMAXINFO	TMinMaxInfo
SEGINFO	TSegInfo
ACCEL	TAccel
PAINTSTRUCT	TPaintStruct
CREATESTRUCT	TCreateStruct
CBT_CREATEWND	TCBT_CreateWnd
MEASUREITEMSTRUCT	TMeasureItemStruct
DRAWITEMSTRUCT	TDrawItemStruct
DELETEITEMSTRUCT	TDeleteItemStruct
COMPAREITEMSTRUCT	TCompareItemStruct
WINDOWPOS	TWindowPos
WINDOWPLACEMENT	TWindowPlacement
NCCALCSIZE_PARAMS	TNCCalcSize_Params
SIZE	TSize
MENUITEMTEMPLATEHEADER	TMenuItemTemplateHeader
MENUITEMTEMPLATE	TMenuItemTemplate
DCB	TDCB
COMSTAT	TComStat
MDICREATESTRUCT	TMDICreateStruct
CLIENTCREATESTRUCT	TClientCreateStruct
MULTIKEYHELP	TMultiKeyHelp
HELPWININFO	THelpWinInfo
CTLSTYLE	TCtlStyle
CTLtype	TCtltype
CTLINFO	TCtlInfo
DDEADVISE	TDDEAdvise
DDEDATA	TDDEData
DDEPOKE	TDDEPoke
DDEAACK	TDDEAck
DEVMODE	TDevMode
KANJISTRUCT	TKanjiStruct

 

It's also nice to have access to the translation of the special WINDOWS.H types, which is already done by Borland, and can be found in WINTYPES.PAS (it's a rewarding experience to compare these two files with each other - you'll learn a lot about C and Pascal conversion issues).
Now that we've handled the standard built-in (and Windows) types, let's look at the C type definition of WING_DITHER_TYPE that is present in the WING.H file.

 typedef enum WING_DITHER_TYPE
 {
     WING_DISPERSED_4x4,
     WING_DISPERSED_8x8,
     WING_CLUSTERED_4x4
 } WING_DITHER_TYPE;

This is a so -called enumerated type, and can be translated into an ObjectPascal enumerated type very easily:

 type
   WING_DITHER_TYPE =
    (WING_DISPERSED_4x4,
     WING_DISPERSED_8x8,
     WING_CLUSTERED_4x4);

While most C DLL header files contain only constant definitions (of the form #define XYZ value) and function prototypes, type definitions are also found, and are therefore important to be able to convert.