diff options
| author | Selbi <shadow93x@gmail.com> | 2026-04-08 04:14:20 +0200 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2026-04-08 04:14:20 +0200 |
| commit | 21893ade088fdf0b28f4eebbfda17d94c049e12c (patch) | |
| tree | 7878c75e0797aea1cb31126cb512ced8d0d0ff49 /_inc | |
| parent | 9abe9731014b31a58118f3b0b74a4e15f4b02a55 (diff) | |
| parent | 81f82233b0af62c8cc7c5f4d0a76da11ba5c7e57 (diff) | |
Documented "unknown" REV00 scrolling routines
Diffstat (limited to '_inc')
| -rw-r--r-- | _inc/Level Drawing (REV00).asm | 25 |
1 files changed, 15 insertions, 10 deletions
diff --git a/_inc/Level Drawing (REV00).asm b/_inc/Level Drawing (REV00).asm index 0dbda48..f29e8c3 100644 --- a/_inc/Level Drawing (REV00).asm +++ b/_inc/Level Drawing (REV00).asm @@ -223,6 +223,8 @@ locret_6A80: ; Abandoned unused scroll block code. ; This would have drawn a scroll block that started at 208 pixels down, and was 48 pixels long. +; See Calc_VRAM_Pos_Unknown for more information. +DrawBGScrollBlock_PlaneZ: tst.b (a2) beq.s locret_6AD6 bclr #2,(a2) @@ -234,7 +236,7 @@ locret_6A80: sub.w d1,d4 move.w d4,-(sp) moveq #-16,d5 - bsr.w Calc_VRAM_Pos_Unknown + bsr.w Calc_VRAM_Pos_PlaneZ move.w (sp)+,d4 moveq #-16,d5 moveq #3-1,d6 ; Draw only three rows @@ -250,7 +252,7 @@ loc_6AAC: sub.w d1,d4 move.w d4,-(sp) move.w #320,d5 - bsr.w Calc_VRAM_Pos_Unknown + bsr.w Calc_VRAM_Pos_PlaneZ move.w (sp)+,d4 move.w #320,d5 moveq #3-1,d6 @@ -480,13 +482,16 @@ Calc_VRAM_Pos: ; =========================================================================== ; not used -; This is just like Calc_VRAM_Pos, but seemingly for an earlier -; VRAM layout: the only difference is the high bits of the -; plane's VRAM address, which are 10 instead of 11. -; Both the foreground and background are at $C000 and $E000 -; respectively, so this one starting at $8000 makes no sense. -; sub_6C3C: -Calc_VRAM_Pos_Unknown: +; What this does is swap the background nametable with the window layer in order +; to create a third scrolling layer that appears above the foreground. However, +; this comes at the cost of the background becoming garbled at the bottom of the +; screen, which was likely what contributed in its removal. Internally, it was +; known as "Plane Z", and was also the intended use of the third layout entry. +; Presumably, this (alongside bit 3 of obRender) was what was used to achieve the +; foreground effect seen in the Tokyo Toy Show '90. Ultimately, Sonic 2 repurposed +; this code to draw player 2's foreground in multiplayer. +; sub_6C3C: Calc_VRAM_Pos_Unknown: +Calc_VRAM_Pos_PlaneZ: add.w 4(a3),d4 add.w (a3),d5 andi.w #$F0,d4 @@ -498,7 +503,7 @@ Calc_VRAM_Pos_Unknown: swap d0 move.w d4,d0 rts -; End of function Calc_VRAM_Pos_Unknown +; End of function Calc_VRAM_Pos_PlaneZ ; =========================================================================== ; --------------------------------------------------------------------------- |