15.4.1585  src/lib/x-kit/xclient/src/color/yiq.pkg

## yiq.pkg
#
# YIQ NTSC colorspace -- see http://en.wikipedia.org/wiki/YIQ

# Compiled by:
#     src/lib/x-kit/xclient/xclient-internals.sublib


stipulate
    include package   rw_float_vector;                                                  # Enable   vec[i]   and   vec[i] := f   notations.
    #
    package fv  = rw_float_vector;                                              # rw_float_vector       is from   src/lib/std/rw-float-vector.pkg
herein

    package   yiq
    :         Yiq                                                               # Yiq                   is from   src/lib/x-kit/xclient/src/color/yiq.api
    {
        # We represent a YIQ color value by a
        # packed 3-vector of 64-bit floats holding
        # red, green, blue in that order:
        # 
        Yiq = fv::Rw_Vector;                                                    # This should really be a read-only floatvector, but currently they are not actually a packed type -- See src/lib/std/src/vector-of-eight-byte-floats.pkg XXX BUGGO FIXME.
            #                                                                   # Since we export Rgb as an opaque type, the difference is not critical.

        fun from_floats { y, i, q }                                             # Should do some sort of validation (restriction to [0,1) interval). What exception should we throw? Or should we silently truncate?  XXX BUGGO FIXME.
            =
            {   yiq = fv::make_rw_vector (3, 0.0);

                yiq[0] := y;                                                    # Eventually we'll probably want to suppress index checking here for speed, using unsafe:: operations or whatever. XXX BUGGO FIXME.
                yiq[1] := i;
                yiq[2] := q;

                yiq;
            };

        fun to_floats yiq
            =
            {   y = yiq[0];                                             # Eventually we'll probably want to suppress index checking here for speed, using unsafe:: operations or whatever. XXX BUGGO FIXME.
                i = yiq[1];
                q = yiq[2];

                { y, i, q };
            };


        fun from_rgb  rgb
            =
            {   (rgb::rgb_to_floats rgb) -> (red, green, blue);

                y = 0.30*red + 0.59*green + 0.11*blue;
                i = 0.60*red - 0.28*green - 0.32*blue;
                q = 0.21*red - 0.52*green + 0.31*blue;

                from_floats { y, i, q };
            };

        fun from_name  colorname
            =
            from_rgb  (rgb::rgb_from_floats  (x11_color_name::to_floats  colorname));
    };

end;