Option I:
Bouncing Graphic
1. Create a simple graphic in a square
that is 5x5 or 7x7 pixels in size. Use the colours available in the emulator's
bitmapped display. The graphic could be a ball, a happy face, a logo, an emoji,
or anything else (appropriate!) that you want to use.
2. Encode that graphic in bytes using
DCB (declare constant byte) instructions.
3. Write code to make the graphic bounce
around the screen, reflecting off the edges when it hits. Note: for simplicity,
it is OK if the object always bounces at 45-degree angles.
4. Make the speed keyboard-adjustable
(faster/slower) and perturb the object's path once in a while.
Challenge:
randomize the starting position, and make the object bounce at angles other
than
45 degrees.
< Drawing >
Below code is for drawing shape.
 |
| output |
define WIDTH 5 ; width of graphic
define HEIGHT 5 ; height of graphic
lda #$25 ; 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
draw: lda
data,x ; set the xth value from the data
sta ($10),y ; add y value to address
$10
inx
iny
cpy #WIDTH ; compare Y and width
bne draw ; drawing until y = 5
inc $12 ;
increment row counter
lda #HEIGHT ; are we done yet?
cmp $12 ; compare value of $12 and height. Draw
until last row of data
beq done
lda
$10 ;
clc ; clear carry
adc
#$20 ; add #20 to $10
sta
$10 ; store a value to $10
lda
$11 ; go to page
adc
#$00 ; add #00 to index
sta
$11 ; store a value to $11
ldy
#$00
beq
draw ;branch on equal
done: brk
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
<Moving>
below code is for moving the shape. However, Just move to 45 degree below. It is not perfect yet.
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
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
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
<Add moving>
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
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