Lab 3: Bouncing Graph - Done

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Introduction
In this post, I will show how to do the lab 3: bouncing graphic. The code can be upgraded when I discover an error but the bouncing and moving a ball and applying keyboard part have done. You can understand more this posting if you read my previous postings: Lab 3: Bouncing Graphic (Part 1 - Calculate Pointer) and Lab 3: Bouncing Graph - Drawing and Moving Graph in the Pointer Location. The detailed lab 3 instruction is written below.

 Lab 3 Instruction
The option my group choose is bouncing graphic. The instructions of this option are the following:
  • Create a simple graphic in a square that is 5*5 or 7*7 pixels in size. Use the colors available in the emulator's bit-mapped display. The graphic could be a ball a happy face, a logo, an emoji, or anything else that you want to use
  • Encode that graphic in bytes using DBC (declare constant byte) instructions
  • Write code to make the graphic bounce around the screen, reflecting off the edges when it hits
  • Make the speed keyboard-adjustable (faster/slower) and perturb the object's path once in a while

1. Think about the Steps

1.1. Pseudo Code
  1. Initialize ROW and COLUMN in a certain position (in this posting, #$04 for ROW and #$04 for COLUMN)
  2. Calculate the pointer
  3. Draw the graphic on the bit-mapped output (in this posting, the graphic is a ball)
  4. Check the key. If the key is up, down, right, or left, change the value of ROW or COLUMN
  5. Check the pointer is on the last line. If it is the last line, flip the flag for ROW or COLUMN so it can bounce
  6. Clear the screen the redraw the graphic
  7. Go back to the step 2
1.2. Flow Chart
2. Implementation 
2.1. Define Descriptive Constants
The define descriptive constants for the lab 3 are the following:

  • define  POINTER          $10     
  • define  POINTER_H $11
  • define  ROW_COUNT  $13
  • define  ROW           $14
  • define  COLUMN   $15
  • define CHECK_LINE $16
  • define ROWFLIP_FLAG $17
  • define COLFLIP_FLAG $18 
  • define PTR_CALCULATE $19
  • define DATA_INDEX $20
  • define SCREENCOL_INDEX $21
  • define KEY $22

2.2. Main Functions
Main functions for the lab 3 are the following:

  • Calculate Pointer
  • Draw the Graphic
  • Key Check and Apply the Key
  • Check the graphic is on the top, bottom, right, or left
  • Clear the Screen


 2.3. Whole Code

 define POINTER         $10      
define POINTER_H $11
define ROW_COUNT $13 
define ROW          $14 
define COLUMN  $15
define CHECK_LINE $16 
define ROWFLIP_FLAG $17
define COLFLIP_FLAG $18  
define PTR_CALCULATE $19
define DATA_INDEX $20
define SCREENCOL_INDEX $21
define KEY $22

 define WIDTH 5 
define HEIGHT 5

   lda  #$04          ; Set a row value 1f
  sta ROW
  lda #$04 ; Set a column value 5
  sta COLUMN

 lda #$00
sta ROWFLIP_FLAG
sta COLFLIP_FLAG 

 ; ====== Calculation ======
; ====== Initialize for calculation ======
cal_initialize:

   lda #$00  ; create a pointer at $10
  sta POINTER
  lda #$02
  sta POINTER_H

lda #$00  
sta ROW_COUNT

 lda #$00   
sta PTR_CALCULATE 

 cmp ROW
beq column_count
bne row_count

 ;====== row count =======
row_count:
lda PTR_CALCULATE
clc
adc #$20
sta PTR_CALCULATE

lda POINTER_H
adc #$00
sta POINTER_H

 inc ROW_COUNT 

lda ROW
cmp ROW_COUNT
bne row_count
beq column_count

 ;===== column_count =====
column_count:
  lda PTR_CALCULATE
  clc
  adc COLUMN
sta PTR_CALCULATE

 ;===== store the value to pointer (calculation done) =====
  sta POINTER

 ;===== draw graphic =====
; initializing for drawing graph
lda #$00
sta ROW_COUNT

 ldx #$00 ; index for data
ldy #$00 ; index for screen column

 ; draw graph
draw: lda ball,x

 sta (POINTER),y 

 inx
iny
cpy #WIDTH
bne draw

 inc ROW_COUNT

 lda #HEIGHT 
cmp ROW_COUNT
beq getkey_initialize
  
lda POINTER
clc
adc #$20 
sta POINTER 
lda POINTER_H 
adc #$00
sta POINTER_H  

 ldy #$00 
beq draw

 ; ======= get key =======
getkey_initialize:
txa    
sta DATA_INDEX
tya
sta SCREENCOL_INDEX   
getkey: lda $ff ; get a keystroke 

ldx #$00 ; clear out the key buffer
stx $ff
  cmp #$80 ; if not a cursor key, ignore
  bmi getkey_done
  cmp #$84
  bpl getkey_done 

  cmp #$80 ; check key == up
  bne rightKey_check

  dec ROW ; ... if yes, decrement ROW
  jmp getkey_done

 rightKey_check:
cmp #$81 ; check key == right
  bne downKey_check

  inc COLUMN  ; ... if yes, increment COL
  jmp getkey_done

 downKey_check:
cmp #$82 ; check if key == down 
  bne leftKey_check

  inc ROW ; ... if yes, increment ROW
  jmp getkey_done
 
 leftKey_check:
cmp #$83 ; check if key == left
  bne getkey_done

  dec COLUMN  ; ... if yes, decrement COL
  clc
  bcc getkey_done 

 getkey_done:
ldx DATA_INDEX
ldy SCREENCOL_INDEX
jmp check_location

 ; ======= Check the location ======
check_location: 
jsr check_top
jsr check_bottom
jsr check_right 
jsr check_left
jsr move_pointer

 check_initialize: 
lda #$00
sta CHECK_LINE
rts

check_top:
jsr check_initialize 
lda ROW  
cmp #$01
lda CHECK_LINE
adc #$00
cmp #$00
beq flip_rowFlag
rts

 check_bottom:
jsr check_initialize
lda ROW
cmp #$1b
lda CHECK_LINE
adc #$00
cmp #$01
beq flip_rowFlag 
rts

 check_left:
jsr check_initialize
lda COLUMN
cmp #$01
lda CHECK_LINE
adc #$00
cmp #$00
beq flip_colFlag
rts

 check_right:
jsr check_initialize
lda COLUMN
cmp #$1b
lda CHECK_LINE
adc #$00
cmp #$01
beq flip_colFlag
rts

 ; ======= Flip Row Flag ====== 
flip_rowFlag:
lda ROWFLIP_FLAG
cmp #$00 
beq inc_rowFlag
bne dec_rowFlag
rts

 inc_rowFlag:
inc ROWFLIP_FLAG
rts

 dec_rowFlag:
dec ROWFLIP_FLAG
rts
; ======= Flip Col Flag ======
flip_colFlag:
lda COLFLIP_FLAG
cmp #$00
beq inc_colFlag
bne dec_colFlag
rts

 inc_colFlag:
inc COLFLIP_FLAG
rts

 dec_colFlag:
dec COLFLIP_FLAG
rts

 ; ======= move the graph ======== 
move_pointer:
jsr row_check
jsr col_check
jmp clear

 row_check:
lda ROWFLIP_FLAG
cmp #$01
beq dec_row
bne inc_row

 col_check:
lda COLFLIP_FLAG
cmp #$01
beq dec_col
bne inc_col

 inc_row:
inc ROW
rts

 dec_row:
dec ROW
rts

 inc_col:
inc COLUMN
rts

 dec_col:
dec COLUMN 
rts

 ; ======= move the graph ======= 
;move: inc ROW
; inc COLUMN

 ; ======= clear the screen before redraw the graph =====
clear: lda ball
sta POINTER 
lda #$02
sta POINTER_H

ldy #$00
tya

 clear_loop:
sta (POINTER),y
iny
bne clear_loop

inc POINTER_H
ldx POINTER_H 
cpx #$06
bne clear_loop

jsr cal_initialize

 ; data constant byte
ball:
 dcb 00,03,03,03,00
 dcb 03,07,07,07,03
 dcb 03,07,07,07,03
 dcb 03,07,07,07,03
 dcb 00,03,03,03,00

 3. What I have learned from this lab
When I have completed this lab, I felt this lab was not that much difficult. This is because now I know how to write the following functions in 6502 assembler: 

  • how to calculate the position using the row and column value
  • how to draw the graphic in the bit-mapped screen
  • how to move the graph
  • how to get whether the graph is on the last line or not
  • how to get key
  • how to move the ball using the key user input

Before I have known how to write codes to do those functions, I was struggled to do this lab. I feel proud I have completed this lab.

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