In the previous post, a drawing program was successfully run on 6502 Emulator, now I want to create a kaleidoscope drawing program.
My plan is to allow the user to only draw on the second quadrant which is the top left quadrant in the 6502 display and reflecting whatever the user draw on it to the other three quadrant to create an kaleidoscope effect.
A couple more things needs to be done in order to achieve this.
First it needs to restrict the cursor's movement to only allow user draw on the second quadrant, in drawing cursor by setting the range of row and column to [$00 : $0F] will make this happen.
drawing_cursor: lda ROW ; ensure ROW is in range 0:0F and #$0f sta ROW lda COL ; ensure COL is in range 0:0F and #$0f sta COL ldy ROW ; load POINTER with start-of-row lda table_low,y sta POINTER lda table_high,y sta POINTER_H ldy COL ; store CURSOR at POINTER plus COL lda #CURSOR sta (POINTER),y rts Then whatever pixels that are in the second quadrant should be reflected to other three quadrant. This is done by storing a copy of the current position and adding the x or y offset to the cursor every time user moves the cursor.
drawing_other_quads: LDA POINTER ;; save the pointer to the PHA ;; original location in top_left_quad LDA POINTER_H PHA ; top right quadrant LDA #$10 CLC SBC COL CLC ADC #$10 TAY LDA DOT STA (POINTER),y TYA PHA ; save the y offset ; bottom left quadrant lda #$10 ; load POINTER with start-of-row CLC SBC ROW CLC ADC #$10 TAY lda table_low,y sta POINTER lda table_high,y sta POINTER_H ldy COL ; store CURSOR at POINTER plus COL lda DOT sta (POINTER),y PLA TAY ; bottom right quadrant lda DOT sta (POINTER),y PLA STA POINTER_H PLA STA POINTER RTS Complete source code:
; zero-page variable locations define ROW $20 ; current row define COL $21 ; current column define POINTER $10 ; ptr: start of row define POINTER_H $11 ; constants define DOT $01 ; dot colour location define CURSOR $04 ; purple colour setup: lda #$0f ; set initial ROW,COL sta ROW sta COL LDA #$01 STA DOT draw: jsr drawing_cursor getkey: ldx #$00 ; clear out the key buffer lda $ff ; get a keystroke stx $ff cmp #$30 bmi getkey cmp #$40 bpl continue SEC sbc #$30 tay lda color_pallete, y sta DOT jmp done continue: cmp #$43 ; handle C or c beq clear cmp #$63 beq clear cmp #$80 ; if not a cursor key, ignore bmi getkey cmp #$84 bpl getkey pha ; save A lda DOT ; set current position to DOT sta (POINTER),y jsr drawing_other_quads pla ; restore A cmp #$80 ; check key == up bne check1 dec ROW ; ... if yes, decrement ROW jmp done check1: cmp #$81 ; check key == right bne check2 inc COL ; ... if yes, increment COL jmp done check2: cmp #$82 ; check if key == down bne check3 inc ROW ; ... if yes, increment ROW jmp done check3: cmp #$83 ; check if key == left bne done dec COL ; ... if yes, decrement COL clc bcc done clear: lda table_low ; clear the screen sta POINTER lda table_high sta POINTER_H ldy #$00 tya c_loop: sta (POINTER),y iny bne c_loop inc POINTER_H ldx POINTER_H cpx #$06 bne c_loop done: clc ; repeat bcc draw drawing_cursor: lda ROW ; ensure ROW is in range 0:0F and #$0f sta ROW lda COL ; ensure COL is in range 0:0F and #$0f sta COL ldy ROW ; load POINTER with start-of-row lda table_low,y sta POINTER lda table_high,y sta POINTER_H ldy COL ; store CURSOR at POINTER plus COL lda #CURSOR sta (POINTER),y rts drawing_other_quads: LDA POINTER ;; save the pointer to the PHA ;; original location in top_left_quad LDA POINTER_H PHA ; top right quadrant LDA #$10 CLC SBC COL CLC ADC #$10 TAY LDA DOT STA (POINTER),y TYA PHA ; save the y offset ; bottom left quadrant lda #$10 ; load POINTER with start-of-row CLC SBC ROW CLC ADC #$10 TAY lda table_low,y sta POINTER lda table_high,y sta POINTER_H ldy COL ; store CURSOR at POINTER plus COL lda DOT sta (POINTER),y PLA TAY ; bottom right quadrant lda DOT sta (POINTER),y PLA STA POINTER_H PLA STA POINTER RTS ; these two tables contain the high and low bytes ; of the addresses of the start of each row table_high: dcb $02,$02,$02,$02,$02,$02,$02,$02 dcb $03,$03,$03,$03,$03,$03,$03,$03 dcb $04,$04,$04,$04,$04,$04,$04,$04 dcb $05,$05,$05,$05,$05,$05,$05,$05, table_low: dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 color_pallete: dcb $01,$02,$03,$04,$05,$06,$07,$08,$09,$0a Results:
Top comments (0)