[NTG-context] Re: Can Bytemaps be overwritten?

16 Jun 2025


      Hi Keith,
...
I've been doing some testing to see if bytemaps can be overwritten as a 
way of reusing them and came up with the code below. The MPpage page 1 
should, if my thinking is correct, give three unitsquares coloured red, 
blue, and green. However it seems the squares are all coloured green. To 
get what I expected I rewrote the code as in MPpage page 2, but to get 
the desired outcome I had to create 3 bytemaps. So, does this mean that 
bytemaps can't be overwritten, or am I missing something?
A monday morning head-against-the-wall-banger, this is what you want i 
guess:

\startMPpage %page 1
color newColor;
newbytemap 1 of (250,250,3);
numeric p ; p := 0;
numeric i ; i := 1;
for x := 0 upto 249:
     for y := 0 upto 249:
         if i = 1:
             newColor := \MPcolor{red};
             i := 2;
         elseif i = 2:
             newColor := \MPcolor{blue};
             i := 3;
         else:
             newColor := \MPcolor{green};
             i := 1;
         fi;
         setbyte (x,y) of 1 to (newColor * 255);
     endfor;
endfor;
p := p + 259;
fill
     unitsquare scaled 250 shifted(p - 259,0)
     withbytemap 1;
\stopMPpage

I can explain when banging does help.
...
Best Wishes
Keith
\starttext
\startMPpage %page 1
color newColor;
newbytemap 1 of (250,250,3);
p := 0;
for i = 1 upto 3:
     for x := 0 upto 249:
         for y := 0 upto 249:
             if i = 1:
                 newColor := \MPcolor{red};
             elseif i = 2:
                 newColor := \MPcolor{blue};
             else:
                 newColor := \MPcolor{green};
             fi;
             setbyte (x,y) of 1 to (newColor * 255);
         endfor;
     endfor;
     p := p + 259;
     fill
         unitsquare scaled 250 shifted(p - 259,0)
         withbytemap 1;
endfor;
\stopMPpage
\startMPpage%page 2
color newColor;
p := 0;
for i = 1 upto 3:
     newbytemap i of (250,250,3);
     for x := 0 upto 249:
         for y := 0 upto 249:
             if i = 1:
                 newColor := \MPcolor{red};
             elseif i = 2:
                 newColor := \MPcolor{blue};
             else:
                 newColor := \MPcolor{green};
             fi;
             setbyte (x,y) of i to (newColor * 255);
         endfor;
     endfor;
     p := p + 259;
     fill
         unitsquare scaled 250 shifted(p - 259,0)
         withbytemap i;
endfor;
\stopMPpage
\stoptext
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