''I don't know who made this code, but it generates a one-[pixel] [GIF] of a specified [color].  This is useful for things like [HTML] [barchart]s, where you can specify the height of a bar by defining the height of a one-pixel image.'' -[FW]

(Explain how.)









Primitive:
    proc make_color_dot color {
        return \x47\x49\x46\x38\x37\x61\x01\x00\x01\x00\x91\x00$color\xff\xff\xff\xff\xff\xff\xff\xff\xff\x2c\x00\x00\x00\x00\x01\x00\x01\x00\x00\x02\x02\x44\x01\x00\x3b\x00
            # Hmmm.  In February 2003, CL couldn't get the sequence
            #    above to work as expected, and resorted instead to
        set BEFORE "\x47\x49\x46\x38\x39\x61\x01\x00\x01\x00\x80\x00\x00"
        set AFTER="\x00\x00\x00\x21\xf9\x04\x00\x00\x00\x00\x00\x2c\x00\x00\x00\x00\x01\x00\x01\x00\x00\x02\x02\x44\x01\x00\x3b\x00"
        return $BEFORE$color$AFTER
            # Presumably someone with enough motivation can track
            #    these back to the pertinent standards.
    }


    proc write_color_dot {color filename} {
        set fp [open $filename w]
        puts -nonewline $fp [make_color_dot $color]
        close $fp
    }


    write_color_dot \x00\x00\xff\x00 /tmp/gif/green.gif


----
[[Write up Tk example for simply putting color on PhotoImage.]]



----
[Python]ic expression of same:

     template = [71, 73, 70, 56, 57, 97, 1, 0, 1, 0, 128, 0, 0, 255, 255,
                 255,
                 0, 0, 0, 33, 249, 4, 1, 0, 0, 0, 0, 44, 0, 0, 0, 0, 1,
                 0, 1,
                 0, 0, 2, 2, 68, 1, 0, 59]
     if color:
         rgb = [63, 127, 255] # will be calculated later
         template[13:16] = rgb
         template[22] = 0 # remove transparency    
----
Modern Web programming deprecates spacer gif-s in favor of
[CSS] 
positioning.





[Tcl might not be viable because it is too hard to hire Tcl-savvy employees]