Function ILAPIENTRY iluInvertAlpha

DevIL/src-ILU/src/ilu_manip.cpp:269–331

Inverts the alpha in the image

//! Inverts the alpha in the image
ILboolean ILAPIENTRY iluInvertAlpha() {
	ILuint		i, *IntPtr, NumPix;
	ILubyte		*Data;
	ILushort	*ShortPtr;
	ILfloat		*FltPtr;
	ILdouble	*DblPtr;
	ILubyte		Bpp;

	iluCurImage = ilGetCurImage();
	if (iluCurImage == NULL) {
		ilSetError(ILU_ILLEGAL_OPERATION);
		return IL_FALSE;
	}

	if (iluCurImage->Format != IL_RGBA &&
		iluCurImage->Format != IL_BGRA &&
		iluCurImage->Format != IL_LUMINANCE_ALPHA) {
			ilSetError(ILU_ILLEGAL_OPERATION);
			return IL_FALSE;
	}

	Data = iluCurImage->Data;
	Bpp = iluCurImage->Bpp;
	NumPix = iluCurImage->Width * iluCurImage->Height * iluCurImage->Depth;

	switch (iluCurImage->Type)
	{
		case IL_BYTE:
		case IL_UNSIGNED_BYTE:
			Data += (Bpp - 1);
			for( i = Bpp - 1; i < NumPix; i++, Data += Bpp )
				*(Data) = ~*(Data);
			break;

		case IL_SHORT:
		case IL_UNSIGNED_SHORT:
			ShortPtr = ((ILushort*)Data) + Bpp-1;	
			for (i = Bpp - 1; i < NumPix; i++, ShortPtr += Bpp)
				*(ShortPtr) = ~*(ShortPtr);
			break;

		case IL_INT:
		case IL_UNSIGNED_INT:
			IntPtr = ((ILuint*)Data) + Bpp-1;
			for (i = Bpp - 1; i < NumPix; i++, IntPtr += Bpp)
				*(IntPtr) = ~*(IntPtr);
			break;

		case IL_FLOAT:
			FltPtr = ((ILfloat*)Data) + Bpp - 1;
			for (i = Bpp - 1; i < NumPix; i++, FltPtr += Bpp)
				*(FltPtr) = 1.0f - *(FltPtr);
			break;

		case IL_DOUBLE:
			DblPtr = ((ILdouble*)Data) + Bpp - 1;
			for (i = Bpp - 1; i < NumPix; i++, DblPtr += Bpp)
				*(DblPtr) = 1.0f - *(DblPtr);