diff options
Diffstat (limited to 'scroll/include/globals.s')
| -rw-r--r-- | scroll/include/globals.s | 72 |
1 files changed, 34 insertions, 38 deletions
diff --git a/scroll/include/globals.s b/scroll/include/globals.s index d941736..87a93ea 100644 --- a/scroll/include/globals.s +++ b/scroll/include/globals.s @@ -1,43 +1,39 @@ -;; Resets the background buffer to a zero-sized array. -.macro CLEAR_BACKGROUND_BUFFER - lda #$FF - sta Globals::m_background_buffer -.endmacro - -;; TODO: macro PUSH_TO_BACKGROUND_BUFFER_X - -;; Global variables used throughout the scrolling examples. +;; Global variables used throughout the code base. .scope Globals ;;; - ;; Temporary values. - - m_tmp_1 = $90 - m_tmp_2 = $91 - m_tmp_3 = $92 - - ;; Current value for the scroll on the X axis. - m_scroll = $93 - - m_background_idx = $19 + ;; Argument values as defined in https://github.com/mssola/style.nes. Note + ;; that these variables can also be used as temporary variables. + zp_arg0 = $90 + zp_arg1 = $91 + zp_arg2 = $92 + zp_arg3 = $93 + zp_arg4 = $94 - ;; TODO - m_collisions = $20 - - ;; TODO - m_background_buffer = $40 - - ;; Initialize global variables. - .proc init - lda #0 - sta m_tmp_1 - sta m_tmp_2 - sta m_tmp_3 - sta m_scroll - sta m_background_idx - - CLEAR_BACKGROUND_BUFFER - sta m_collisions + ;;; + ;; Random values that can be used inside of functions for temporary values + ;; so `zp_argX` variables are not overwritten as often. + zp_tmp0 = $9A + zp_tmp1 = $9B + zp_tmp2 = $9C + zp_tmp3 = $9D - rts - .endproc + ;;; + ;; Reserve a byte of memory for preserving indices on memory. This is needed + ;; whenever the `x` and `y` registers might not be reliable because of + ;; underlying `jsr` calls that might tamper with their values. Sometimes + ;; saving the value in memory is enough instead of playing with the stack. + zp_idx = $9E + + ;; Flags that manage the state of the game. + ;; + ;; | Bit | Short name | Meaning when set | + ;; |-----+------------+-------------------------------------------------------------| + ;; | 7 | render | Game logic is over, block main code until NMI code is over. | + ;; | 6 | ppu | PPU registers (2000 and scroll) have to be updated. | + ;; | 5 | level | The current level is active. | + ;; | 4 | column | The current column is still being buffered into the PPU. | + ;; | 3 | end | We are at the end of the level | + ;; | 2 | nametable | Next nametable to be used | + ;; | 1-0 | - | Unused | + zp_flags = $20 .endscope |