VDU extensions
==============

VDU 17,n - text colour
----------------------
&00+n - foreground text colour
&40+n - extensions
&80+n - background text colour
&C0+n - border colour

VDU 18,a,c - GCOL
-----------------
action
b0-b2: plot action
 0 SET Set pixel
 1 ORA ORA with corrent pixel
 2 AND AND with current pixel
 3 XOR XOR with current pixel
 4 NOT Invert pixel
 5 NUL Do nothing
 6 CLR Clear pixel to background
 7 UND Undefined

b3:    transparent background

&00+x Line drawing
&10+x ECF pattern 1
&20+x ECF pattern 2
&30+x ECF pattern 3
&40+x ECF pattern 4
&50+x All four ECF patterns
&60+x Superpattern
&70+x 

&80+x 
&90+x 
&A0+x Reserved
&B0+x 
&C0+x 
&D0+x 
&E0+x For application use: GCOL -17,n to GCOL -32,n
&F0+x For application use: GCOL  -1,n to GCOL -16,n

&89,window - select window     : &89, 137, -119, -ASC"w"
&8C,style  - set to font style : &8C, 140, -114, -ASC"s"
&8D,style  - add to font style : &8D, 141, -115, -ASC"t"


VDU 19,l,p,r,g,b - set palette
------------------------------

VDU 23
------
VDU 23,18,option,set,mask,0,0,0,0 - Teletext control

VDU 23,19,option,.... - Framebuffer control
         <&40         - control
          &40+n       - select font by name
         >&5F         - reserved