Lab 3

 define WIDTH 	5 ; width of graphic
 define HEIGHT 	5 ; height of graphic

 	lda #$00	; create a pointer at $10
 	sta $10		;   which points to where
 	lda #$02	;   the graphic should be drawn
 	sta $11
  
 	lda #$00	; number of rows we've drawn
 	sta $12		;   is stored in $12
 
 	ldx #$00	; index for data
 	ldy #$00	; index for screen column

move: 
	jsr clearScreen
	;brk
	jsr moveDown
	jsr moveRight
	;draw will modify our pointer, we need to backup and reset it later
	lda $10
	sta $14;backup
	lda $11
	sta $15 
	jsr draw
	lda $14
	sta $10;reset
	lda $15
	sta $11
	;brk
	jsr move 
 
 draw:	
	lda data,x
 	sta ($10),y 
 	inx
 	iny 
 	cpy #WIDTH 
	;brk
 	bne draw
   
 	inc $12		; increment row counter
 
 	lda #HEIGHT	; are we done yet?
 	cmp $12
 	bne continue	; if not equal, go to continue
	;beq done;	; comment out bne continue and beq done > movin

	;lda $04;
	;sta $11
	ldx #$00; //reset index
	ldy #$00;
	sty $12
	rts
  
continue: 	 
	;brk;
	lda $10		; load pointer
 	clc 
 	adc #$20	; add 32 to drop one row
 	sta $10
 	lda $11	; carry to high byte if needed
 	adc #$00
	cmp #$06
	beq done
 	sta $11 
 
 	ldy #$00
 	beq draw
	;rts
  
 done:	brk		; stop when finished
	;rts
 
 data:
 dcb 00,03,03,03,00
 dcb 07,00,00,00,07
 dcb 07,00,00,00,07
 dcb 07,00,00,00,07
 dcb 00,03,03,03,00

moveRight: 	
	sty $13
	ldy $10
	iny	
	sty $10
	ldy $13
	rts

moveDown: 
	lda $10
	clc
	adc #$20 ;add a line
	sta $10
	lda $11
	adc #$00
	cmp #$06
	beq done
	sta $11
	rts

resetPage:
	lda #$02
	sta $11
	rts

clearScreen: ;we can create another sub route called clearPrevious to avoid flashing screen
	sta $22 ;backup registers
	stx $23
	sty $24	

	lda #$00	;   create a pointer at $80
 	sta $20		;   which points to where
 	lda #$02	;   the graphic should be drawn
 	sta $21
	lda #$00 ;black color
	ldy #$00 ;
mloop:
	sta ($20), y
	iny
	bne mloop
	
	ldx $21
	inx
	stx $21
	cpx #$06
	bne mloop

	lda $22 ;revert registers
	ldx $23
	ldy $24
	rts

The code above is what I’ve done so far.

In Lab 3 our group will create a shape that will bounce around that will reflect when it reaches screen edge.

So far, the shape is able to move from top left to bottom right. But when the it is drawing the picture at bottom right, it will write data to 0x0600, where our program located. Then the program crushed.

Procedure:

When the program starts, we load the image from dcb data. and draw it at the address where our pointer point at. Then we modify the pointer, clear screen, then draw it again.

move: 
	jsr clearScreen
	;brk
	jsr moveDown
	jsr moveRight
	;draw will modify our pointer, we need to backup and reset it later
	lda $10
	sta $14;backup
	lda $11
	sta $15 
	jsr draw
	lda $14
	sta $10;reset
	lda $15
	sta $11
	;brk
	jsr move 

However, draw modifies our pointer to complete drawing, therefore, we backed it up and restored it after drawing finished. After restoring pointer, we come back to move sub route, and clear screen again, then modify our pointer and draw it again.

clearScreen: ;we can create another sub route called clearPrevious to avoid flashing screen
	sta $22 ;backup registers
	stx $23
	sty $24	

	lda #$00	;   create a pointer at $80
 	sta $20		;   which points to where
 	lda #$02	;   the graphic should be drawn
 	sta $21
	lda #$00 ;black color
	ldy #$00 ;
mloop:
	sta ($20), y
	iny
	bne mloop
	
	ldx $21
	inx
	stx $21
	cpx #$06
	bne mloop

	lda $22 ;revert registers
	ldx $23
	ldy $24
	rts

Clear screen is simple. we fill 00 from address 0x0200 until 0x05FF. But it is very slow. This is planned to be optimized. Because we know where we drew, so we just need to erase that addresses.

moveRight: 	
	sty $13
	ldy $10
	iny	
	sty $10
	ldy $13
	rts

moveDown: 
	lda $10
	clc
	adc #$20 ;add a line
	sta $10
	lda $11
	adc #$00
	cmp #$06
	beq done
	sta $11
	rts

moveRight and moveDown is also simple.

In moveRight, we just increased pointer index by 1, so it moves right 1 pixel. But the shape does not reflect after it reaches right edge. We need to check if it reaches right edge and change the increase so decrease if it reaches right edge.

In moveDown, we increase pointer index by 32(hex 20). if there is a borrow, it means we need to switch page(e.g. from 0x0200 to 0x0300), so we add 0. if there is a borrow, it will add 1 instead of 0.

We will finish this lab next week. We plan to create an X and Y coordinator function to manage where our shape is, so we can easily to deal with the reflection issue.

To be continued!