Wednesday, June 27, 2007

XeO3: Scripting Engine.

Okay, after a request for more info on the scripting engine/system I use, I've written up a small description of how it all works. It's not hugely in-depth, but it should give you the jist on how it all works...

So have a look HERE to read through, but feel free to ask questions afterwards. I do intend to write up an API for the script system, and do several examples and tutorials for when I release the code. I've some some small samples and doc's so that Luca and play with it, but I really need to do far more.
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4 comments:

  1. Anonymous6/28/2007 9:04 am

    Thanks. How deep is the mini stack? Just one entry? Subroutines (just one level) could be useful for cramming more data into the game, but that depends a lot on the attack patterns.

    I would like to see the inner working of CIRCLE command. I remember you writing about it last year, but that entry didn't go too deep into the details.



    DoNextCommand:
    ldy #0 ; reset index into command
    lda (PathAddress),y ; get command
    asl a ; *2 to index table
    tay

    How about using commands which are *2 already :)


    ; Move absolute

    iny
    clc
    lda (PathAddress),y ; get move-to "X"
    bpl DoAddX

    adc SpxLo,x
    bcs SkipAddX
    dec SpxHi,x
    bcc SkipAddX

    DoAddX:
    adc SpxLo,x
    bcc SkipAddX
    inc SpxHi,x

    SkipAddX:
    sta SpxLo,x

    iny
    clc
    lda Spy,x
    adc (PathAddress),y
    sta Spy,x

    jmp DoNextPathAddY

    ; ...

    DoNextPathAddY:
    sec
    tya
    adc PathAddress
    sta PathAddress
    bcc DoNextPath
    inc PathAddress+1
    DoNextPath:


    Saves some cycles/bytes. If DoNextPath() works like I think, you can add Y+1 to PathAddress and store it directly to PAlo/PAhi table.


    --
    TNT

    ReplyDelete
  2. Iapetus6/28/2007 1:46 pm

    Thank you Mike =D

    Keep up the good work, looking forward for the playable demo.

    ciao

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  3. Mike6/28/2007 6:04 pm

    I don't actually have a DoNextPath() call in the 6502 source, but I probably would in a higher level langauge.

    Optimisation is a skill of picking your fights, and aside from the circle command, I dont think the rest of the script system takes up that much - sprite drawing is by far the largest system, followed by scrolling.

    Thats not to say I wont look at it.... just not yet :)

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  4. Mike6/28/2007 6:43 pm

    I dont use CALL's in XeO3, and only allow 1 deep FOR statements. This is a limitation due to memory and speed. I have done these on faster systems though.

    So basically, the mini-stack is only 1 entry deep.

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