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@ -4,7 +4,6 @@ org $7530
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; System variables
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tv_flag EQU $5c3c ; TV flags
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last_k EQU $5c08 ; Last pressed key
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clr_screen EQU $0daf ; ROM routine to clear the screen
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; Screen is 256x192
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@ -22,45 +21,46 @@ start
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push bc
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call clear_screen ; Clear the screen
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call initStars ; Initialize the number of stars defined in MAX_STARS
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call init_stars ; Initialize the number of stars defined in MAX_STARS
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main_start
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ld hl, STARS ; Points to X
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ld c, MAX_STARS
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ld hl, STARS ; points to X
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ld c, MAX_STARS ; Set counter value
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main
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; CLEAR THE LAST POSITION
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ld de, $3 ; Skip to PrevX
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add hl, de
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push bc ; save MAX_STARS in the stack
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ld de, $3
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add hl, de ; skip to PrevX
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ld a, (hl)
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ld d, a ; Save PrevX to D
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inc hl ; PrevY
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inc hl ; points to PrevY
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ld a, (hl)
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ld e, a ; Save PrevY to E
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push bc
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push hl
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call get_screen_address
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; Video RAM address for those X,Y is now in HL and the bit needed
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; to be set in that address value is in A
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call clear_pixel ; Uses those values clears the pixel
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call clear_pixel ; Uses those values and clears the pixel
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pop hl
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ld bc, $4 ; Go back to X
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sbc hl, bc
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ld bc, $4
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sbc hl, bc ; Go back to X
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pop bc
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; WRITES THE PIXEL
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ld a, (hl) ; HL points to X
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ld a, (hl) ; HL should point to X
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ld d, a ; Save X to D
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inc hl ; Y
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inc hl ; points to Y
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ld a, (hl)
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ld e, a ; Save Y to E
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push bc
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push hl
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call get_screen_address
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; Video RAM address for those X,Y is now in HL and the bit needed
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@ -68,12 +68,12 @@ main
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call write_pixel ; Uses those values and writes the pixel
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pop hl
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ld bc, $4 ; Jump 4 positions - Next star
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add hl, bc
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pop bc
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ld bc, $4
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add hl, bc ; Skip 4 positions to the next star
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pop bc ; Remove counter from stack
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dec c ; Decrement counter
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jr nz, main ; Repeat if not zero
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call increment_x ; Increment X position in each star
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@ -89,7 +89,7 @@ table
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db 82,97,120,111,102,116,20,12
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get_rnd
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push bc ; Guarda o valor de RET na stack
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push bc
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get_rnd_loop
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push de
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@ -149,54 +149,55 @@ get_rnd_loop
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get_rnd_ret
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ld a, h
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pop bc ; Tira o valor de RET da stack
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and a ; Reset carry
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pop bc
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ret
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ENDP
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PROC
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; Initialize stars X and Y with "random" values
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initStars
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init_stars
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push bc
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ld d, MAX_STARS ; Number of stars to process
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ld hl, STARS ; HL points to X of first start
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ld hl, STARS ; HL points to X of first star
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ld c, MAX_STARS ; Number of stars to process
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initStars_loop
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push de
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init_stars_loop
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push bc
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push hl
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ld d, 1
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ld e, 255
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call get_rnd ; Get a random value <= 255
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call get_rnd ; Get a random value between 1 and 255
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pop hl
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ld (hl), a ; Set X to random value
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ld (hl), a ; Set X value
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inc hl ; points to Y
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push hl
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ld d, 1
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ld e, 191
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call get_rnd
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call get_rnd ; Get a random value between 1 and 191
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pop hl
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ld (hl), a ; Set Y to random value
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ld (hl), a ; Set Y value
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inc hl ; points to Speed
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push hl
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ld d, 1
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ld e, 10
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call get_rnd ; Get a random value <= 255
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call get_rnd ; Get a random value between 1 and 10
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pop hl
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ld (hl), a ; Set Speed to random value
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ld (hl), a ; Set Speed value
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ld bc, $3 ; Jump to next star
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add hl, bc ; Skip PrevX and PrevY
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ld bc, $3
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add hl, bc ; Skip 3 bytes to the next star
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pop de
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dec d ; Decrement counter
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jr nz, initStars_loop ; If not zero, do it again
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pop bc
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dec c ; Decrement counter
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jr nz, init_stars_loop ; If not zero, do it again
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pop bc
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ret
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@ -208,6 +209,7 @@ increment_x
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push bc
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ld hl, STARS
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ld c, MAX_STARS
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increment_x_loop
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; First lets copy current position to previous position
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ld d, (hl) ; Save current X to D
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@ -221,15 +223,14 @@ increment_x_loop
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ld (hl), e ; Save Y
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ld de, $4
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sbc hl, de ; Go back to X
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sbc hl, de ; Go back 4 bytes to X
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ld a, (hl) ; Is X at $FF - end of screen
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cp $ff
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jr z, increment_x_zero ; Yes, lets reset
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jr z, increment_x_zero ; Yes, lets reset it
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; Increments X position by speed value
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; X = X + Y
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; X = X + Speed
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inc hl ; points to Y
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inc hl ; points to Speed
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@ -245,8 +246,8 @@ increment_x_update
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; Saves to X the value in A
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ld (hl), a ; Save X with the value in A
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ld de, $5 ; Skip 5 bytes to the next star
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add hl, de
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ld de, $5
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add hl, de ; Skip 5 bytes to the next star
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dec c ; Decrement counter
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jr nz, increment_x_loop ; If not zero, do it again
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@ -265,7 +266,7 @@ increment_x_zero
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call get_rnd
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pop hl
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ld (hl), a ; Set Y = getRandomY
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ld (hl), a ; Set Y value
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inc hl ; point to speed
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@ -275,9 +276,7 @@ increment_x_zero
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call get_rnd
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pop hl
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ld (hl), a ; Set Speed = getRandomSpeed
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and a ; Reset carry
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ld (hl), a ; Set Speed value
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ld de, $2
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sbc hl, de ; Get back to X position
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