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Playfield Variables vs Playfield (and data table)


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I was trying something out and didn't quite get the results I was thinking would happen so I wanted to get a better understanding as to why.


My program's space is limited.  I am trying to finish things up but I have the following space remaining in each of the banks:


      1 bytes of ROM space left in bank 1
      41 bytes of ROM space left in bank 2
      6 bytes of ROM space left in bank 3
      6 bytes of ROM space left in bank 4


I had thought that instead of using the drawing the entire playfield like this:


I could only use certain playfield variables and rewrite a couple of lines and save some space by doing this:

 var16=%00000000 :var17=%01110110 :var18=%11101100 :var19=%01110111 
 var20=%00111111 :var21=%00010001 :var22=%10101010 :var23=%00010010 
 var24=%01101010 :var25=%00010001 :var26=%11101100 :var27=%01100010 
 var28=%01010101 :var29=%01110001 :var30=%10101010 :var31=%01110010 
 var32=%00111111 :var33=%00000000 :var34=%00000000 :var35=%00000000 
 var36=%00011110 :var37=%11111110 :var38=%11111111 :var39=%01111111 
 var40=%00110011 :var41=%00000000 :var42=%00000000 :var43=%00000000 

I had used playfield variables in my game when I needed to change just a small portion of the screen like maybe a couple pixels so I thought this could be an easy way to save space but when I tried to compile I got an error message that listed the remaining bytes as such:


segment:  3fd4          eqm       vs current org: 3ffd
      1 bytes of ROM space left in bank 1
      41 bytes of ROM space left in bank 2
      -41 bytes of ROM space left in bank 3


The code I was changing was in bank 3 but my question is why would drawing 7 lines of the playfield using playfield variable use more space then drawing the entire thing with "x"s and "."s?


Also, when I tried instead using a data table instead I saved space but I couldn't figure out how to read the data, and if that would be a better solution? 

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12 minutes ago, Random Terrain said:

Thanks.  I never noticed this before on your page so I just tried it and the results are the same:


 Routine 1:  57   (playfield)
 Routine 2:  144  (playfield variables)
 Routine 3:  47    (data table)


I had thought that if I just used a couple playfield variables I would have used much less.  The results were surprising. Basically, in my code I had the screens change but I was thinking that since half of the screen stays the same I could save space by just redrawing half the screen so I was wondering about the workings of the code to understand the differences.

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Also, try something like this to see if it helps (untested):


    for temp5 = 0 to 27
        var17[temp5] = my_screen[temp5]

    data my_screen
    %00000000, %01110110, %11101100, %01110111
    %00111111, %00010001, %10101010, %00010010 
    %01101010, %00010001, %11101100, %01100010 
    %01010101, %01110001, %10101010, %01110010 
    %00111111, %00000000, %00000000, %00000000 
    %00011110, %11111110, %11111111, %01111111 
    %00110011, %00000000, %00000000, %00000000


Edit: Also, don't forget that the bit order is reversed for the odd-numbered variables, assuming you haven't already taken that into account in your data.

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I had thought about setting a temp variable and doing it that way but I don't think I have any left. Thanks for the answer. It is interesting to hear the going on under the hood. I had a similar question last year as I was working on Crossdock but that was when I switch from using pfpixel to the playfield variables so I just assumed the difference would be great. 


Thank you for your response but I will definitely play around with this in the future. I was looking for creative ways to try and save space in my program (or future programs).

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