Fade in and out for ZX Spectrum

example.asm

; Example code for Fade-In and Fade-Out

	DEVICE ZXSPECTRUM128
	ORG 40000
	INCBIN "my_picture.scr"
	ORG 30000

TEST
	EI
	CALL CLR_ATTR

	; Set to image origin and prepare the fade in
	LD HL,40000 
	CALL APPEAR_INIT

	; Perform ALOOP 7 times for 7 bits of attributes (we don't use FLASH color here)
	LD B,7
ALOOP
	; Preserve counter
	LD HL,(iterator)
	LD (HL),B
	; Set to image attr origin and do step
	LD HL,46144
	CALL APPEAR_STEP
	; Wait 2 frames
    LD B,2
    CALL WAIT
	; Restore iterator
    LD HL,(iterator)
    LD B,(HL)
	DJNZ ALOOP

	; Wait ~1s before going to fade out
	LD B,50
	CALL WAIT

	; Prepare the fade out
	CALL DISAPPEAR_INIT

	; 7 times BLOOP for 7 bits again
	LD B,7
BLOOP
	; Preserve counter
	LD HL,(iterator)
	LD (HL),B
	; Do step
	CALL DISAPPEAR_STEP
	; Wait 2 frames
    LD B,2
    CALL WAIT
	; Restore iterator
    LD HL,(iterator)
    LD B,(HL)
	DJNZ BLOOP

	; Wait ~1s before going to fade in
	LD B,50
	CALL WAIT

	; Repeat forever
	JP TEST


; A procedure for waiting
WAIT: ; -- B must be number of frames
	  HALT
	  DJNZ WAIT
	  RET

iterator defb 0 ; to preserve the loop counter

	INCLUDE "genscreen.asm" ; Load the generic screen operations
	INCLUDE "fx.fadein.asm" ; Load the fade in
	INCLUDE "fx.fadeout.asm" ; Fade out

	SAVESNA "fade.test.sna",TEST

fx.fadein.asm

; ------------------------------------------------------------------
APPEAR_INIT	; HL -- must point to image area start
			LD DE,SCREEN_AREA ; Video buffer
			LD BC,SCREEN_SZ ; Only data
			LDIR ; Copy area
			LD A,0 ; Reset mask to 0
			LD (APPEAR_MSK),A
			RET
; -------------------------------------------------------------------
APPEAR_STEP ; HL -- must point to attr area of original
			LD A,(APPEAR_MSK) ; Current color mask
			RLA ; Shift mask left
			SET 0,A ; Set 1st bit of mask again
			BIT 7,A ; Check if we are reaching FLASH 
			JR NZ, _APP_DONE ; If FLASH, abandon the thing because all colors are in place now
			LD (APPEAR_MSK),A ; Save mask for next step
			LD DE,ATTR_AREA ; Beginning of screen color memory

			LD B,255 ;  pass of 255 items
_APP_LOOP1	LD A,(APPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (DE),A ; Write it to the screen
			INC HL
			INC DE
			DJNZ _APP_LOOP1
			LD B,255 ;  pass of 255 items
_APP_LOOP2	LD A,(APPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (DE),A ; Write it to the screen
			INC HL
			INC DE
			DJNZ _APP_LOOP2
			LD B,255 ;  pass of 255 items
_APP_LOOP3  LD A,(APPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (DE),A ; Write it to the screen
			INC HL
			INC DE
			DJNZ _APP_LOOP3
			LD B,3 ;  pass of 255 items
_APP_LOOP4  LD A,(APPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (DE),A ; Write it to the screen
			INC HL
			INC DE
			DJNZ _APP_LOOP4
_APP_DONE	RET


; -------------------------------------------------------------------

APPEAR_MSK db 0

fx.fadeout.asm

; ------------------------------------------------------------------
DISAPPEAR_INIT	
			LD A,127 ; Reset mask to all on
			LD (DISAPPEAR_MSK),A
			RET
; -------------------------------------------------------------------
DISAPPEAR_STEP 
			LD A,(DISAPPEAR_MSK) ; Current color mask
			OR A ; Clear carry
			RRA ; Shift mask right
			LD (DISAPPEAR_MSK),A ; Save mask for next step
			LD HL,ATTR_AREA ; Beginning of screen color memory

			LD B,255 ;  pass of 255 items
_DISAP_L1	LD A,(DISAPPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (HL),A ; Write it to the screen
			INC HL
			DJNZ _DISAP_L1
			LD B,255 ;  pass of 255 items
_DISAP_L2	LD A,(DISAPPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (HL),A ; Write it to the screen
			INC HL
			DJNZ _DISAP_L2
			LD B,255 ;  pass of 255 items
_DISAP_L3  LD A,(DISAPPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (HL),A ; Write it to the screen
			INC HL
			DJNZ _DISAP_L3
			LD B,3 ;  pass of 255 items
_DISAP_L4   LD A,(DISAPPEAR_MSK) ; Copy mask to accumulator
			LD C,(HL) ; Copy current byte of original
			AND C ; Bitwise and of mask and original
			; Now A contains the resulting attribute
			LD (HL),A ; Write it to the screen
			INC HL
			DJNZ _DISAP_L4
_DISAP_DONE	RET


; -------------------------------------------------------------------

DISAPPEAR_MSK db 0

genscreen.asm

	DEFINE ATTR_AREA 22528
	DEFINE ATTR_SZ 767
	DEFINE SCREEN_AREA 16384
	DEFINE SCREEN_SZ 6144
; -------------------------------------------------------------------

CLR_ATTR
		LD HL,ATTR_AREA
		LD A,0
		LD B,255
CLLP1	LD (HL),A ; Copy 0 to screen color area
		INC HL
		DJNZ CLLP1
		LD B,255
CLLP2	LD (HL),A ; Copy 0 to screen color area
		INC HL
		DJNZ CLLP2
		LD B,255
CLLP3	LD (HL),A ; Copy 0 to screen color area
		INC HL
		DJNZ CLLP3
		LD B,3
CLLP4	LD (HL),A ; Copy 0 to screen color area
		INC HL
		DJNZ CLLP4
		RET

; -------------------------------------------------------------------

CLS		CALL #0D6B
		RET

; -------------------------------------------------------------------