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Part 3: creating first version of "game loop" code, moving snowballs …
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…on screen

- there are 32 snowballs travelling at screen at two different speeds
and left or right direction
- there is one static player sprite standing at bottom
- first version of game loop added:
-- uploads all sprites from memory to HW sprite engine
-- modify sprite data in memory for next frame
-- loop infinitely all that stuff

The result does "work", except everything is sort of too fast...
something to resolve in Part 4.
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@ped7g
ped7g committed Feb 2, 2020
1 parent 0207b60 commit 372d6c2
Showing 1 changed file with 121 additions and 24 deletions.
145 changes: 121 additions & 24 deletions SpecBong.asm
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,13 @@

OPT --zxnext=cspect ;DEBUG enable break/exit fake instructions of CSpect (remove for real board)

STRUCT S_SPRITE_4B_ATTR ; helper structure to work with 4B sprites attributes
x BYTE 0 ; X0:7
y BYTE 0 ; Y0:7
mrx8 BYTE 0 ; PPPP Mx My Rt X8 (pal offset, mirrors, rotation, X8)
vpat BYTE 0 ; V 0 NNNNNN (visible, 5B type=off, pattern number 0..63)
ENDS

; selecting "Next" as virtual device in assembler, which allows me to set up all banks
; of Next (0..223 8kiB pages = 1.75MiB of memory) and page-in virtual memory
; with SLOT/PAGE/MMU directives as needed, to assemble code/data to different parts
Expand Down Expand Up @@ -116,39 +123,128 @@ UploadSpritePatternsLoop:
dec a
jr nz,UploadSpritePatternsLoop ; do 64 patterns

; create DEBUG 8x8 grid of sprites, showing all the patterns currently uploaded
ld c,$57 ; sprite pattern-upload I/O port
; sprite index is already set to 0 above, where the pattern slot was set to 0
ld hl,$2020 ; X (H) = 32, Y (L) = 32
; byte 3 (D) = +0 palette offset, no mirror/rotation, X.msb=0
; byte 4 (E) = visible sprite = 1, 4B type (0), pattern 0
ld de,%0000'0'0'0'0'1'0'000000
DebugSpriteGridLoopRow:
ld b,8 ; 8 sprites per single row in grid
DebugSpriteGridLoopSingleSprite:
; upload 4B type of sprite attributes
out (c),h ; X
out (c),l ; Y
out (c),d ; pal.offset, mirrors/rotate, X.msb
out (c),e ; visible, 4B type, pattern number
; advance position and pattern
inc e ; ++pattern for next sprite
add hl,24<<8 ; X += 24
djnz DebugSpriteGridLoopSingleSprite
add hl,((-24*8)<<8) + 24 ; X -= 24*8, Y += 24
; ------------------------------------------------------------------------------------
; Part 3 - creating base main-loop, moving few sprites around, no controls yet
; ------------------------------------------------------------------------------------

; init 32 snowballs and one player - the in-memory copy of sprite attributes
; init them at some debug positions, they will for part 3 just fly around mindlessly
ld ix,SprSnowballs ; IX = address of first snowball sprite
ld b,32 ; define 32 of them
ld hl,0 ; HL will generate X positions
ld e,32 ; E will generate Y positions
ld d,$80 + 52 ; visible sprite + snowball pattern (52, second is 53)
InitBallsLoop:
; set current ball data
ld (ix+S_SPRITE_4B_ATTR.x),l
ld (ix+S_SPRITE_4B_ATTR.y),e
ld (ix+S_SPRITE_4B_ATTR.mrx8),h ; clear pal offset, mirrors, rotate, set x8
ld (ix+S_SPRITE_4B_ATTR.vpat),d
; adjust initial position and pattern for next ball
add hl,13 ; 13*32 = 416: will produce X coordinates 0..511 range only
ld a,e
cp 8*8 + $80 ; sprite visible flag + pattern == 64 -> end loop
jr nz,DebugSpriteGridLoopRow ; until all 0..63 sprites/patterns are set
add a,5
ld e,a ; 5*32 = 160 pixel spread vertically
ld a,d
xor 1 ; alternate snowball patterns between 52/53
ld d,a
; advance IX to point to next snowball
push de
ld de,S_SPRITE_4B_ATTR
add ix,de
pop de
djnz InitBallsLoop
; init player at debug position
ld ix,SprPlayer
ld (ix+S_SPRITE_4B_ATTR.x),32+16 ; near left of paper area
ld (ix+S_SPRITE_4B_ATTR.y),206 ; near bottom of paper area
ld (ix+S_SPRITE_4B_ATTR.mrx8),0 ; clear pal offset, mirrors, rotate, x8
ld (ix+S_SPRITE_4B_ATTR.vpat),$80 + 2 ; pattern "2" (player

; main loop of the game - first version for Part 3
; (will have many shortcoming, to be resolved in later parts of tutorial)
GameLoop:
; upload sprite data from memory array to the actual HW sprite engine
; reset sprite index for upload
ld bc,$303B
xor a
out (c),a ; select slot 0 for sprite attributes
ld hl,Sprites
ld bc,$57 ; B = 0 (repeat 256x), C = sprite pattern-upload I/O port
; out 512 bytes in total (whole sprites buffer)
otir
otir
; adjust sprite attributes in memory pointlessly (in debug way) just to see some movement
call SnowballsAI

; do the infinite loop to not run some random memory content as code
jr $
; do the GameLoop infinitely
jr GameLoop

;-------------------------------------------------------------------------------------
; "AI" subroutines

SnowballsAI:
ld ix,SprSnowballs
ld de,S_SPRITE_4B_ATTR
ld b,32
.loop:
; HL = current X coordinate (9 bit)
ld l,(ix+S_SPRITE_4B_ATTR.x)
ld h,(ix+S_SPRITE_4B_ATTR.mrx8)
; adjust it by some +- value deducted from B (32..1 index)
ld c,0 ; mirrorX flag = 0
ld a,b
and 3 ; A = 0,1,2,3
sli a ; A = 1, 3, 5, 7
sub 4 ; A = -3, -1, +1, +3
; do: HL += signed(A) (the "add hl,a" is "unsigned", so extra jump+adjust needed)
jr nc,.moveRight
dec h
ld c,$08 ; mirrorX flag = 1
.moveRight:
add hl,a
; put H and C together to work as palette_offset/mirror/rotate bits with X8 bit
ld a,h
and 1 ; keep only "x8" bit
or c ; add desired mirrorX bit
; store the new X coordinate and mirror/rotation flags
ld (ix+S_SPRITE_4B_ATTR.x),l
ld (ix+S_SPRITE_4B_ATTR.mrx8),a
; alternate pattern between 52 and 53
ld a,(ix+S_SPRITE_4B_ATTR.vpat)
xor 1
ld (ix+S_SPRITE_4B_ATTR.vpat),a
add ix,de ; next snowball
djnz .loop ; do 32 of them
ret

;-------------------------------------------------------------------------------------
; data area

; reserve full 128 sprites 4B type (this demo will not use 5B type sprites)
ALIGN 256 ; aligned at 256B boundary w/o particular reason (yet)
Sprites:
DS 128 * S_SPRITE_4B_ATTR, 0
; "S_SPRITE_4B_ATTR" works as "sizeof(STRUCT), in this case it equals to 4

; the later sprites are drawn above the earlier, so for Part 3 the sprites
; 0..31 will be used for snowballs, and sprite 32 for player
; adding symbols to point inside the memory reserved above
SprSnowballs: EQU Sprites + 0*S_SPRITE_4B_ATTR ; first snowball sprite at this address
SprPlayer: EQU Sprites + 32*S_SPRITE_4B_ATTR ; player sprite is here

;-------------------------------------------------------------------------------------
; reserve area for stack at $B800..$BFFF region
ORG $B800
DS $0800-2, $AA
initialStackTop:
DW $AAAA

;-------------------------------------------------------------------------------------
; game data in different (later) banks, pre-loaded in sjasm virtual device memory
; so they get stored in the NEX file, and loaded by NEX loader to desired bank
;-------------------------------------------------------------------------------------

; pre-load the image pixel data from TGA file into memory (to store it in NEX file)
; the pixel data will be in 16k banks 9, 10, 11 (8k pages: 18, 19, .., 23)
; We will use the last page region $E000..$FFFF to map through all the pages and
Expand All @@ -175,6 +271,7 @@ BackGroundPalette:
SpritePixelData:
INCBIN "SBsprite.spr"

;-------------------------------------------------------------------------------------
; all the data are in the virtual-device memory, now dump it into NEX file
SAVENEX OPEN "SpecBong.nex", start, initialStackTop, 0, 2 ; V1.2 enforced
SAVENEX CORE 3, 0, 0 ; core 3.0.0 required
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