Function ilAddAlphaKey

DevIL/src-IL/src/il_convert.cpp:679–885

Adds an alpha channel to an 8 or 24-bit image, making the image transparent where Key is equal to the pixel.

// Adds an alpha channel to an 8 or 24-bit image,
//	making the image transparent where Key is equal to the pixel.
ILboolean ilAddAlphaKey(ILimage *Image)
{
	ILfloat KeyRed = 0, KeyGreen = 0, KeyBlue = 0, KeyAlpha = 0;
        ILubyte		*NewData, NewBpp;
	ILfloat		KeyColour[3];
	ILuint		i = 0, j = 0, c, Size;
	ILboolean	Same;

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

	if (Image->Format != IL_COLOUR_INDEX) {
		if (Image->Bpp != 3) {
			ilSetError(IL_INVALID_VALUE);
			return IL_FALSE;
		}

		if (Image->Format == IL_BGR || Image->Format == IL_BGRA) {
			KeyColour[0] = KeyBlue;
			KeyColour[1] = KeyGreen;
			KeyColour[2] = KeyRed;
		}
		else {
			KeyColour[0] = KeyRed;
			KeyColour[1] = KeyGreen;
			KeyColour[2] = KeyBlue;
		}

		Size = Image->Bps * Image->Height / Image->Bpc;

		NewBpp = (ILubyte)(Image->Bpp + 1);
		
		NewData = (ILubyte*)ialloc(NewBpp * Image->Bpc * Image->Width * Image->Height);
		if (NewData == NULL) {
			return IL_FALSE;
		}

		switch (Image->Type)
		{
			case IL_BYTE:
			case IL_UNSIGNED_BYTE:
				for (; i < Size; i += Image->Bpp, j += NewBpp) {
					NewData[j]   = Image->Data[i];
					NewData[j+1] = Image->Data[i+1];
					NewData[j+2] = Image->Data[i+2];
					Same = IL_TRUE;
					for (c = 0; c < Image->Bpp; c++) {
						if (Image->Data[i+c] != KeyColour[c] * UCHAR_MAX)
							Same = IL_FALSE;
					}

					if (Same)
						NewData[j+3] = 0;  // Transparent - matches key colour
					else
						NewData[j+3] = UCHAR_MAX;
				}