diff options
| -rw-r--r-- | src/player.s | 84 |
1 files changed, 35 insertions, 49 deletions
diff --git a/src/player.s b/src/player.s index dc87cb0..210a7c1 100644 --- a/src/player.s +++ b/src/player.s @@ -1,5 +1,28 @@ .segment "CODE" +;; Translate the given fixed-point 16-bit position into screen coordinates and +;; leave it into the `a` register. +;; +;; NOTE: see the documentation on player's movement for more information. +.macro FIXED_POINT_POSITION_TO_SCREEN POS_ADDR + ;; We save the high byte into a temporary value, and we load the low byte + ;; into the accumulator. + lda POS_ADDR + 1 + sta Globals::zp_tmp0 + lda POS_ADDR + + ;; And now it's a matter of rotating the high byte into the low one to + ;; match a full byte. + lsr Globals::zp_tmp0 + ror + lsr Globals::zp_tmp0 + ror + lsr Globals::zp_tmp0 + ror + lsr Globals::zp_tmp0 + ror +.endmacro + ;; Functions and variables that keep up with the player's sprite. That is, ;; movement, heading, animation, collision with the environment, etc. .scope Player @@ -158,11 +181,19 @@ sta zp_walk_counter @to_screen: - ;; At this point all positions are clear, transform them into screen - ;; coordinates, eject out from boundaries and platforms, and update the - ;; sprite with the new state. - jsr position_to_screen + ;; Translate fixed-point positions to screen coordinates. + FIXED_POINT_POSITION_TO_SCREEN zp_position_y + sta zp_screen_y + FIXED_POINT_POSITION_TO_SCREEN zp_position_x + sta zp_screen_x + + ;; We have the newly proposed screen coordinates. Now let's check if + ;; that collides with some background element. If that's the case, + ;; handle ejection logic now. jsr background_check + + ;; And with that, update all the sprites with the information we have + ;; collected (i.e. heading, throttle, coordinates). JAL update_sprites .endproc @@ -342,51 +373,6 @@ rts .endproc - ;; Convert the positions with subpixel precision into mere screen - ;; coordinates. That is, update the values on `zp_screen_{x,y}` given the - ;; current values of `zp_position_{x,y}`. - .proc position_to_screen - ;; We save the high byte into a temporary value, and we load the low - ;; byte into the accumulator. - lda zp_position_y + 1 - sta Globals::zp_tmp0 - lda zp_position_y - - ;; And now it's a matter of rotating the high byte into the low one to - ;; match a full byte. - lsr Globals::zp_tmp0 - ror - lsr Globals::zp_tmp0 - ror - lsr Globals::zp_tmp0 - ror - lsr Globals::zp_tmp0 - ror - - ;; Ecce Y coordinates. - sta zp_screen_y - - ;; And the same for the X coordinates. - lda zp_position_x + 1 - sta Globals::zp_tmp0 - lda zp_position_x - - ;; And rolling... - lsr Globals::zp_tmp0 - ror - lsr Globals::zp_tmp0 - ror - lsr Globals::zp_tmp0 - ror - lsr Globals::zp_tmp0 - ror - - ;; Ecce X coordinates. - sta zp_screen_x - - rts - .endproc - ;; Check on whether the player is out of bounds in any way and provide an ;; ejection logic for each situation. .proc background_check |