(*
This is a simple demonstration file for the Zeus assembler.
If you want more sustantial files they're available at www.desdes.com

These are just some jottings to help, so they'll just touch on the subjects... 


Structures.

These are a handy way to generate the offset values for (IX+NN) index operations.

Imagine we do the following (which indeed you can do)

	org 0
dpNext	ds 2		; Value = 0 A two byte variable
dX	ds 2		; Value = 2 A two byte variable
dY	ds 2		; Value = 4     "      "
dFlags	ds 1		; Value = 6 A byte variable

Then we could use those labels as follows:

	ld a,(ix+dFlags); ie (IX+6)

(Note that I put a 'd' on the front to indicate they're displacements. You don't
have to do this, it's just a nice reminder)...

Which is all fine and dandy except that we can't just move the PC around in the
middle of the source unless we do ugly things with variables to save it... So, a
while back Zeus added the "STRUCT" / "SEND" convention which effectively saves the
PC in a stack and restores it again.

Let's see it in operation:
*)

	org $6000
		
Start	nop		; Addr 6000
	nop		; Addr 6001
	
    struct
dpNext	ds 2		; Value = 0
dX	ds 2		; Value = 2
dY	ds 2		; Value = 4
dFlags	ds 1		; Value = 6
lStar	equ .		; Value = 7 (The length of this structure)
    send

    struct
dopNext	ds 2		; Value = 0
doFlags	ds 1		; Value = 2
lThing	equ .		; Value = 3 (The length of this structure)
    send

	nop		; Addr 6002
	nop		; Addr 6003

// Show the results
zeusprint "Structure A ",dpNext,dX,dY,dFlags,lStar
zeusprint "Structure B ",dopNext,doFlags,lThing


(*
You can nest structures, but gawd knows why you'd want to do this. Zeus will prevent
you from trying to plant data in a structure definition, you're only allowed "ds"
operations.

You can also put a label on the send, which will return the length of the structure.

    struct		;
Fred	db 1		; This is illegal and will generate an error.
    send		;

*)

; The fp_euq.asm source in the FP sources shows these used to good effect.
; Much nicer than a list of "Blah equ 42" statements? No? Oh, well, suit yourself ;)
;
; Excerpt from FP:

	struct
dpnObje 	ds 2
dppObje		ds 2
dpnFreeObje	ds 2
dObjeX		ds 2
dObjeY		ds 2
dObjeZ		ds 2
dObjedX		ds 2
dObjedY		ds 2
dObjedZ		ds 2
dObjeOX		ds 2
dObjeOY		ds 2
dObjeOZ		ds 2
dObjeDispXL	ds 2
dObjeDispXR	ds 2
dObjeDispYT	ds 2
dObjeDispYB	ds 2
dObjepLines	ds 2*8		; There are 8 line pointers, each 16-bits
dObjepDraw      ds 1
dObjepUnDraw    ds 1
dObjeDraw	ds 2
dObjeShot	ds 2
dObjeColl	ds 2
dObjeMiss	ds 2
dObjeAlter	ds 2
dObjeMove	ds 2
dObjeFlags      ds 1
dObjeStateF     ds 1
dObjeStarComp   ds 1
dObjeAXS	ds 2
dObjeAYS	ds 2
dObjepSizeTab	ds 2
dObjeCnt        ds 1
dObjeBdXS	ds 2
dObjeBdYS	ds 2
dObjeBXS	ds 2
dObjeBYS	ds 2
dObjeWindF      ds 1
dObjeCol        ds 1
dObjeCntA       ds 1
dObjeCntiA      ds 1
dObjeCntB       ds 1
dObjeCntiB      ds 1
dObjeWidthX     ds 1
dObjeWidthY     ds 1
dObjeClipFlags  ds 1
dObjeWeapon     ds 1
	
        ; These variables overlap the line pointers

dObjeFFH1	equ dObjepLines+2
dObjeFFH2	equ dObjepLines+4
dObjeFFV1	equ dObjepLines+6
dObjeFFV2	equ dObjepLines+8

lObje           equ .
	send





(*

This next command tells Zeus where to put the code it generates. As a szx file...
It has three parameters, the filename, where the stack should go and where to start
Alter the path to suit your system, of course.
*)
	output_szx "c:\zt2.szx",$0000,Start	; The szx file
(*
The output_szx can appear wherever you like in the file. If there's more than one of
them the last one will be the one used.
*)

(*
If for some reason you want raw binary, include this line
It has three parameters, the filename, start of block and length
*)

;	output_bin "c:\zt2.bin",$0000,$10000	; The binary file

(*
Note that I've commented it out. Normally it wouldn't be, of course.

The output_bin can appear wherever you like in the file. If there's more than one of
them the last one will be the one used.

If both output types appear, both files will be written.
*)