From Retrosoftware

Current revision

16/11/2010: Objects and Engine State

First up: I realised that the extra lda workbuffer above is superfluous (though not the cmp). I could have saved the flags register to stack, but I gain nothing by doing this.

This time I've been doing the code to manage objects. This is a bit more complicated than just searching through for present objects. As objects can be moved during the lifetime of the adventure they need to be stored in the save area, along with other data used by the engine (e.g. flags, counters, current room etc). So, I've reserved a page to keep this information in and set it up at gameinit. The routine's quite simple: blank out the main area, then copy object locations and information from the game header (player start room, light length).

The advantage of keeping this contiguous is that when I implement SAVE GAME and LOAD GAME, all I need to do is save and load to this page of memory!

Finally I added the code to print out present objects. As the text is in the standard tokenised format, this was easy enough (code reuse is really useful).

One potential problem that I'm seeing is the amount of 16 bit updates I'm doing. This is leading to a lot of code of the style:

{.objectloop   lda objectlocs,x
               cmp currentroom
               beq printobject
.nextobject inx
               cpx nitems
               bne objectloop
               jmp leave
.printobject stx xstore
               txa
               jsr findobject
               lda foundptr
               clc
               adc #2
               sta foundptr
               bcc prtobj
               inc foundptr+1
.prtobj      jsr copymessage
               ldx #workbuffer MOD 256
               ldy #workbuffer DIV 256
               jsr printbuf
               ldx xstore
               jmp nextobject
}

There must be an easier way to manage a 16-bit number than just doing inc loc(or adc); bne (or bcc); inc loc+1. I'm starting to wish I was doing this on a Z80 now!

A quick update ere the day ends. To test the exits code I added a very quick way of navigating around the adventure (i.e. a hack - I just read N, S, E, W, U, D from the keyboard and move in that direction).

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