Function ILAPIENTRY ilSetAlpha

DevIL/src-IL/src/il_manip.cpp:962–1044

sets the Alpha value to a specific value for each pixel in the image

// sets the Alpha value to a specific value for each pixel in the image
ILboolean ILAPIENTRY ilSetAlpha(ILdouble AlphaValue)
{
	ILboolean	ret = IL_TRUE;
	ILuint		i,Size;
	ILimage		*Image = iCurImage;
	ILuint		AlphaOff;

	if (Image == NULL) {
		ilSetError(IL_ILLEGAL_OPERATION);
		return IL_FALSE;
	}

	AlphaValue = IL_CLAMP(AlphaValue);

	switch (Image->Format)
	{
		case IL_RGB:
			ret = ilConvertImage(IL_RGBA, Image->Type);
		case IL_RGBA:
			AlphaOff = 4;
		break;
		case IL_BGR:
			ret = ilConvertImage(IL_BGRA, Image->Type);
		case IL_BGRA:
			AlphaOff = 4;
			break;
		case IL_LUMINANCE:
			ret = ilConvertImage(IL_LUMINANCE_ALPHA, Image->Type);
		case IL_LUMINANCE_ALPHA:
			AlphaOff = 2;
			break;
		case IL_ALPHA:
			AlphaOff = 1;
		case IL_COLOUR_INDEX: //@TODO use palette with alpha
			ret = ilConvertImage(IL_RGBA, Image->Type);
			AlphaOff = 4;
			break;
	}
	if (ret == IL_FALSE) {
		// Error has been set by ilConvertImage.
		return IL_FALSE;
	}
	Size = Image->Width * Image->Height * Image->Depth * Image->Bpp;

	switch (iCurImage->Type)
	{
		case IL_BYTE: 
		case IL_UNSIGNED_BYTE: {
			const ILbyte alpha = (ILubyte)(AlphaValue * IL_MAX_UNSIGNED_BYTE + .5);
			for (i = AlphaOff-1; i < Size; i += AlphaOff)
				Image->Data[i] = alpha;
			break;
		}
		case IL_SHORT:
		case IL_UNSIGNED_SHORT: {
			const ILushort alpha = (ILushort)(AlphaValue * IL_MAX_UNSIGNED_SHORT + .5);
			for (i = AlphaOff-1; i < Size; i += AlphaOff)
				((ILushort*)Image->Data)[i] = alpha;