256 zooming circles by Defence Force [web]
; --------------------------------------
; 256 bytes moving backgound mini demo
; --------------------------------------
; (c) 2006 Mickael Pointier
Just a small prod I made in 2006 for a Club Europe Oric magazine's article on size coding using the OSDK.
Nothing fabulous, that was my first attempt at doing a 256 bytes anything on the Oric :)
What it does is basically to trick the ROM in believing we are in High resolution mode (so we can use graphic primitives as lines and circles) while staying in Text mode. Then a small section (24x24 pixels) of the (non visible) Hires screen that contains the animation is copied to the charmap. Since the same block of 4x3 characters is repeated all over the screen it gives this mirroring illusion.
Dbug
--------------------------------
;
; ROM & RAM system defines
; (Works only on ROM 1.1)
;
#define _rom_hires $ec33
#define _rom_curset $f0c8
#define _rom_circle $f37f
#define ROM_PARAMS $2e0
#define ROM_PATTERN $213
#define ROM_CURX $219
#define ROM_CURY $21a
#define INK_BLUE 4
#define FB_DRAW 1
#define SCREEN_HIRES $a000
#define CHARSET_TEXT $b400+8*"@"
#define SCREEN_TEXT $bb80
#define SCREEN_LAST $bfdf
#define SCREEN_SRC_OFFSET (-40*24)+1
.zero
*= $50
circle_ray .dsb 1
tmp0 .dsb 1
tmp1 .dsb 1
ptr_src .dsb 2
ptr_src2 .dsb 2
ptr_dst .dsb 2
.text
_main
; Switch to hires
jsr _rom_hires
; Erase the parameter area
lda #0
ldx #7
loop
sta ROM_PARAMS-1,x
dex
bne loop
; Force "manualy" the text mode by setting a 50hz TEXT switch attribute
lda #26
sta SCREEN_LAST
; More CPU time, and no more blinking cursor !
sei
.(
;
; Let's fill screen with a pattern of characters, for example that:
;
; @CFI
; ADGJ
; BEHK
;
lda #0
sta tmp0
sta tmp1
lda #<SCREEN_TEXT
sta ptr_src+0
lda #>SCREEN_TEXT
sta ptr_src+1
ldx #28
loop_y
ldy #39
loop_x
.(
lda tmp0
bne skip
lda #12
skip
sec
sbc #3
sta tmp0
.)
clc
lda #"@"
adc tmp0
adc tmp1
; Write character in video memory
sta (ptr_src),y
dey
bne loop_x
sty tmp0
; End of line, we write the color attribute at the begining,
; and update line pointers...
lda #INK_BLUE
sta (ptr_src),y
.(
clc
lda tmp1
adc #1
cmp #3
bne skip
lda #0
skip
sta tmp1
.)
jsr IncPtrSrc
dex
bne loop_y
.)
lda #FB_DRAW
sta ROM_PARAMS+3 ; Set the FB parameter to "draw"
BigLoop
.(
; Draw a first animated circle
ldx circle_ray
inx
txa
and #15
sta circle_ray
; Draw two circles
ldx #2
loop_circle
stx tmp0
lda CircleData-1,x
sta ROM_CURX
sta ROM_CURY
ldx circle_ray
inx
stx ROM_PARAMS+1
jsr _rom_circle
ldx tmp0
dex
bne loop_circle
.)
; Pattern register
inc ROM_PATTERN
.(
;
; Let's dump a 24x24 pixels area of the HIRES screen to the redefined characters area :D
;
lda #<SCREEN_HIRES
sta ptr_src+0
lda #>SCREEN_HIRES
sta ptr_src+1
lda #<CHARSET_TEXT
sta ptr_dst+0
lda #>CHARSET_TEXT
sta ptr_dst+1
ldx #4
loop_x
stx tmp0
ldx #24
loop_y
; Compute the secondary pointer to create the mirror picture
clc
lda ptr_src+0
adc #<40*24
sta ptr_src2+0
lda ptr_src+1
adc #>40*24
sta ptr_src2+1
ldy #4
lda (ptr_src),y ; Top right
ora (ptr_src2),y ; Bottom right
ldy #0
ora (ptr_src),y ; Top left
ora (ptr_src2),y ; Bottom left
; Update the char map
sta (ptr_dst),y
; Clean the HIRES buffer
lda #64
sta (ptr_src),y
sta (ptr_src2),y
ldy #4
sta (ptr_src),y
sta (ptr_src2),y
jsr IncPtrSrc
.(
inc ptr_dst+0
bne skip
inc ptr_dst+1
skip
.)
dex
bne loop_y
clc
lda ptr_src+0
adc #<SCREEN_SRC_OFFSET
sta ptr_src+0
lda ptr_src+1
adc #>SCREEN_SRC_OFFSET
sta ptr_src+1
ldx tmp0
dex
bne loop_x
.)
jmp BigLoop
IncPtrSrc
.(
clc
lda ptr_src+0
adc #40
sta ptr_src+0
bcc skip
inc ptr_src+1
skip
.)
rts
CircleData
.byt 12,24
.byt "-DBUG-"[ back to the prod ]