diff options
Diffstat (limited to 'src/player.s')
| -rw-r--r-- | src/player.s | 107 |
1 files changed, 92 insertions, 15 deletions
diff --git a/src/player.s b/src/player.s index ce8794f..af5572b 100644 --- a/src/player.s +++ b/src/player.s @@ -40,9 +40,14 @@ INIT_X_POSITION_LO = $00 INIT_X_POSITION_HI = $07 - THROTTLE = $D8 - BLAST_OFF = $F8 - GRAVITY = $28 + ;; Different acceleration/velocity constants. + GRAVITY = $28 + THROTTLE_UP = $D8 + THROTTLE_LEFT = $D8 + THROTTLE_RIGHT = $28 + BLAST_OFF = $F8 + WALK_LEFT = $F8 + WALK_RIGHT = $08 zp_screen_y = $40 zp_position_y = $41 ; NOTE: 16-bit. @@ -112,10 +117,20 @@ lda #(Joypad::BUTTON_UP | Joypad::BUTTON_A) and Joypad::zp_buttons1 beq @set_gravity + + ;; Player is throttling, reflect that on the player's state. + lda #%10000100 + ora zp_state + sta zp_state + + ;; If the current velocity is zero, then we are "blasting off", and a + ;; bit of animation plus special velocity should occur. Otherwise we + ;; should apply the regular throttle velocity. lda zp_velocity_y beq @blast_off - lda #THROTTLE + lda #THROTTLE_UP bne @compute_vertical + @set_gravity: lda #GRAVITY @@ -172,39 +187,101 @@ sbc #0 sta zp_position_y + 1 - ;; Player is throttling. - lda #%10000100 - ora zp_state - sta zp_state - rts .endproc .proc update_horizontal_position - ;; - ;; TODO - ;; - lda #Joypad::BUTTON_LEFT and Joypad::zp_buttons1 beq @check_right + ;; We are facing left, reflect that on the state and the sprite. lda #%10111111 and zp_state ora #%00000100 sta zp_state - jmp @end + ;; If we are throttling, then we need to apply the proper acceleration + ;; for it. Otherwise, if walking, then there's no acceleration and the + ;; velocity is linear, so we just set the velocity and directly apply + ;; it, skipping the whole acceleration part. + bit zp_state + bmi @left_throttle + lda #WALK_LEFT + sta zp_velocity_x + bne @apply_velocity + @left_throttle: + lda #THROTTLE_LEFT + bne @apply_acceleration + ;; Same as the part above but applied to going right. @check_right: lda #Joypad::BUTTON_RIGHT and Joypad::zp_buttons1 - beq @end + beq @nothing lda #%01000100 ora zp_state sta zp_state + bit zp_state + bmi @right_throttle + lda #WALK_RIGHT + sta zp_velocity_x + bne @apply_velocity + @right_throttle: + lda #THROTTLE_RIGHT + bne @apply_acceleration + + ;; If neither left nor right is being pressed, go for a zero + ;; acceleration, which will slow down the player instead of going to a + ;; full stop. + @nothing: + lda #0 + + ;; As with vertical motion, `a` contains the acceleration to aim for, + ;; and we just subtract the current velocity and see if we either have + ;; to accelerate or decelerate to reach that, and we do that with steps. + @apply_acceleration: + ;; TODO: as with vertical motion, mind NTSC vs PAL + sta Globals::zp_tmp0 + lda zp_velocity_x + sec + sbc Globals::zp_tmp0 + beq @apply_velocity + bmi @accelerate_left + dec zp_velocity_x + jmp @apply_velocity + @accelerate_left: + inc zp_velocity_x + + ;; With the final velocity already at hand, update the position with it. + @apply_velocity: + lda zp_velocity_x + bmi @going_left + + ;; The velocity is positive, so it's just a 16-bit addition. + clc + adc zp_position_x + sta zp_position_x + lda #0 + adc zp_position_x + 1 + sta zp_position_x + 1 + rts + + @going_left: + lda #0 + sec + sbc zp_velocity_x + sta Globals::zp_tmp0 + lda zp_position_x + sec + sbc Globals::zp_tmp0 + sta zp_position_x + lda zp_position_x + 1 + sbc #0 + sta zp_position_x + 1 + @end: rts .endproc |