Z80 Good Programming Practices

Using IX

If you have objects represented by adjacent chunks of data in memory, you can use IX to easily manage them.

 ld b,10
 ld hl,SpritesData
DisplaySpritesLoop
 ld b,(hl) ; coordx
 inc hl
 ld c,(hl) ; coordy
 inc hl
 ld d,(hl) ; first part of address
 inc hl
 ld e,(hl) ; end of address
 inc hl
 call DisplaySprite
 djnz DisplaySpritesLoop
 

COORDX equ. 0
COORDY equ. 1
ADDR1 equ. 2
ADDR2 equ. 3

 ld b,10
 ld ix,SpritesData
DisplaySpritesLoop
 ld b,(ix+COORDX)
 ld c,(ix+COORDY)
 ld d,(ix+ADDR1)
 ld e,(ix+ADDR2)
 call DisplaySprite
 ld hl,4
 add ix,hl
 djnz DisplaySpritesLoop
 

Defining constants for the offsets of each field of your "objects" makes the code more understandable.

Lookup table

If you have a place in your code where a value is tested to choose between a lot of things, like subroutines or data, it can be a good idea to use lookup tables instead of a series of tests. It makes the code more readable, concise and extensible.

 ld a,(SpriteNumber)
 cp 1
 jp z,ChooseSprite1
 cp 2
 jp z,ChooseSprite2
 cp 3
 jp z,ChooseSprite3
 cp 4
 jp z,ChooseSprite4
...
ChooseSprite1
 ld hl,Sprite1
 jp DisplaySprite
ChooseSprite2
 ld hl,Sprite2
 jp DisplaySprite
ChooseSprite3
 ld hl,Sprite3
 jp DisplaySprite
ChooseSprite4
 ld hl,Sprite4
 jp DisplaySprite
...
DisplaySprite
 ld bc,(coordinates)
 call SpriteRoutine

Can be rewritten in :

 ld a,(SpriteNumber)
 add a,a ; a*2
 ld h,O 
 ld l,a 
 ld de,SpriteAddressLUT
 add hl,de
 ld bc,(coordinates)
 call SpriteRoutine
...
SpriteAddressLUT
 .dw Sprite1
 .dw Sprite2
 .dw Sprite3
 .dw Sprite4
 

And this one :

 ld a,(MenuChoice)
 cp 1
 jp z,Choice1
 cp 2
 jp z,Choice2
 cp 3
 jp z,Choice3
 cp 4
 jp z,Choice4
...
 

Can be rewritten in :

 ld a,(MenuChoice)
 add a,a ; a*2
 ld h,O
 ld l,a
 ld de,CodeBranchLUT
 add hl,de
 jp (hl)
...
CodeBranchLUT
 .dw Choice1
 .dw Choice2
 .dw Choice3
 .dw Choice4
 

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