248 lines
6.5 KiB
Plaintext
248 lines
6.5 KiB
Plaintext
processor 6502
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include "vcs.h"
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include "macro.h"
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org $f000
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; Now, we'll finally put everything together and
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; make a little person with a hat that can move
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; back and forth and throw rocks. We'll use one player
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; to generate a 8x16 sprite and one missile.
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;
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; We have two tables for the sprite, a bitmap table and
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; a color table. We'll lookup from both of these tables on
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; each scanline.
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;
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; Because VCS programming is all about thrift, we'll
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; reuse the machine code for our program as the backdrop
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; for the playfield, just to show we can fit it all on
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; a scanline.
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;
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; Note: the Y coordinate goes bottom-top, not top-bottom
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; as in the next section.
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counter equ $81 ; increments each frame
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yplyr equ $82 ; player y pos
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yrock equ $83 ; rock y pos
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animofs equ $84 ; sprite data offset, used for animation
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; Initialize and set initial offsets of objects.
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start CLEAN_START
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lda #5
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sta yplyr
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lda #70
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ldx #0
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jsr SetHorizPos ; set player 0 horiz. pos
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sta WSYNC
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sta HMOVE
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; Next frame loop
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nextframe
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VERTICAL_SYNC
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; in case the rock is on screen
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lda ColorFrame0 ; load 1st entry of color data
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sta COLUP0 ; set sprite 0 color
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; 37 lines of VBLANK
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ldx #37
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lvblank sta WSYNC
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dex
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bne lvblank
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; set some colors
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lda #$80
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sta COLUBK ; set the background color
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lda #1
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sta CTRLPF ; playfield reflection
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; Draw 192 scanlines with our sprite/missile kernel
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ldx #192
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lvscan
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; Draw sprite?
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txa
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sec ; make sure carry is set (meaning no borrow for subtraction)
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sbc yplyr ; get offset into sprite for this line
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cmp #SpriteHeight ; sprite is 16 pixels high + padding on either side
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bcc insprite
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lda #SpriteHeight-1 ; draw the padding
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insprite
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tay
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lda ColorFrame0,y ; load color data
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pha ; push color data onto stack
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clc ; clear carry flag
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adc animofs ; add animation offset (not for color though)
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lda Frame0,y ; load bitmap data
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sta WSYNC ; wait for next scanline (as late as possible!)
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sta GRP0 ; set sprite 0 pixels
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pla ; pull bitmap data from stack
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sta COLUP0 ; set sprite 0 color
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lda start,x ; store some random garbage into the playfield
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sta PF0
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sta PF1
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sta PF2
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; Draw rock? Player 0 and missile 0 share a color register,
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; so they will have the same colors on the same scanline
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lda #%00000000
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cpx yrock
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bne norock
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lda #%00000010 ; for ENAM0 the 2nd bit is enable
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norock
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sta ENAM0 ; enable missile 0
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dex
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bne lvscan ; repeat next scanline until finished
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; End of scanline loop
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; Clear all colors to black before overscan
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stx COLUBK
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stx COLUP0
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stx COLUP1
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stx COLUPF
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; 30 lines of overscan
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ldx #29
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lvover sta WSYNC
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dex
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bne lvover
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; Joystick movement
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; For up and down, we INC or DEC the Y Position
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lda #%00010000 ;Up?
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bit SWCHA
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bne SkipMoveUp
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inc yplyr
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SkipMoveUp
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lda #%00100000 ;Down?
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bit SWCHA
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bne SkipMoveDown
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dec yplyr
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SkipMoveDown
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; Note that the horizontal position is not contained in RAM,
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; but inaccessibly inside the TIA's registers! Some games can
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; get away with this if they use the collision registers.
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ldx #0 ; assume speed is 0 if no movement
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lda #%01000000 ;Left?
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bit SWCHA
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bne SkipMoveLeft
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ldx #$10 ;a 1 in the left nibble means go left
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SkipMoveLeft
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lda #%10000000 ;Right?
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bit SWCHA
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bne SkipMoveRight
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ldx #$F0 ;a -1 in the left nibble means go right...
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SkipMoveRight
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stx HMP0 ;set the move for plyr 0
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sta WSYNC
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sta HMOVE
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; Throw a rock when fire button pressed
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lda #0
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sta animofs
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ldy #%00000000 ; use later to enable/disable missile lock on player
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lda INPT4 ;read button input
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bmi ButtonNotPressed ;skip if button not pressed
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lda yplyr
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sta yrock ; set rock vert pos to player's vert
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lda #SpriteHeight
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sta animofs ; while button pressed, use alternate player bitmap
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ldy #%00000010 ; for RESMP0 the 2nd bit is the enable bit
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ButtonNotPressed
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sty RESMP0 ; reset missile 0 to player 0's horiz position
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inc yrock ; rock moves no matter what (actually a boomerang)
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; Goto next frame
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jmp nextframe
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; SetHorizPos - Sets the horizontal position of an object.
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; The X register contains the index of the desired object:
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; X=0: player 0
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; X=1: player 1
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; X=2: missile 0
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; X=3: missile 1
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; X=4: ball
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; This routine does a WSYNC and HMOVE before executing,
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; so whatever you do here will not take effect until you
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; call the routine again or do your own WSYNC and HMOVE.
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SetHorizPos
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sta WSYNC ; start a new line
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sta HMOVE ; apply the previous fine position(s)
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sta HMCLR ; reset the old horizontal position(s)
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sec ; set carry flag
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DivideLoop
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sbc #15 ; subtract 15
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bcs DivideLoop ; branch until negative
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eor #7 ; calculate fine offset
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asl
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asl
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asl
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asl
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sta RESP0,x ; fix coarse position
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sta HMP0,x ; set fine offset
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rts ; return to caller
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; Height of our sprite in lines
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SpriteHeight equ 18
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; Bitmap data "standing" position
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Frame0
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.byte #0
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.byte #%01101100;$F6
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.byte #%00101000;$86
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.byte #%00101000;$86
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.byte #%00111000;$86
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.byte #%10111010;$C2
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.byte #%10111010;$C2
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.byte #%01111100;$C2
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.byte #%00111000;$C2
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.byte #%00111000;$16
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.byte #%01000100;$16
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.byte #%01111100;$16
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.byte #%01111100;$18
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.byte #%01010100;$18
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.byte #%01111100;$18
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.byte #%11111110;$F2
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.byte #%00111000;$F4
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; Bitmap data "throwing" position
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Frame1
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.byte #0
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.byte #%01101100;$F6
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.byte #%01000100;$86
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.byte #%00101000;$86
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.byte #%00111000;$86
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.byte #%10111010;$C2
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.byte #%10111101;$C2
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.byte #%01111101;$C2
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.byte #%00111001;$C2
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.byte #%00111000;$16
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.byte #%01101100;$16
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.byte #%01111100;$16
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.byte #%01111100;$18
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.byte #%01010100;$18
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.byte #%01111100;$18
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.byte #%11111110;$F2
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.byte #%00111000;$F4
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; Color data for each line of sprite
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ColorFrame0
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.byte #$FF ; rock color if not sharing line with player sprite
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.byte #$F6;
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.byte #$86;
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.byte #$86;
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.byte #$86;
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.byte #$C2;
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.byte #$C2;
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.byte #$C2;
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.byte #$C2;
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.byte #$16;
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.byte #$16;
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.byte #$16;
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.byte #$18;
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.byte #$18;
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.byte #$18;
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.byte #$F2;
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.byte #$F4;
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; Epilogue
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org $fffc
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.word start
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.word start
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