Specifies a graphics object whose alpha or luminosity is to be used as a soft mask for this graphics state.
The Graphics object must have a transparency group associated with it via the PdfGraphics.SetGroup method.
This method can only be used
if this object represents a graphics state object (IsGroup = False).
Param is a PdfParam object or parameter string. The following parameters (all optional) are supported:
- Alpha (Boolean) - if True, specifies that the alpha values of Graphics are to be used for the soft mask.
If False or omitted, the luminocity values of Graphics are to be used. In the latter case, the transparency group associated with
Graphics must have a color space linked to it via the SetColorSpace method.
- C0, C1, ..., Cn - the color components in the range 0.0 to 1.0 specifying the color to be used
as the backdrop against which to composite the transparency group. Only used if Alpha is False or omitted.
The number of color components must match the color space linked to the transparency group associated with Graphics.
For more information, see Section 17.4 - Soft Masks.
