[S1] Considerably speeding up level loading

So, the other day as I was browsing through my old projects, I found a project that I had been working on but never completed, and since I came up with ways to considerably speed up level loading, I thought I could share with you. Why you'd want to use this? Well, I don't... Gotta go fast, right??!!
Bear in mind I will use Sonic 1 HiveBrain disassembly, so for SVN/Hg/Git, reference only. I am unsure whether or not will it work with Sonic 2 or Sonic 3/Knuckles/3 and Knuckles. Most of these are compatible with each other and can be applied fairly easily, however if its not the case, and is known, will be stated in the description

Method 1: Title card art optimization

Spoiler

Extra ROM usage: 2546 (0x09F2) bytes
Extra RAM usage: 0
Optimization level: Great

So, one very long process the game does each time you load up level, is load title card art. This is nemesis compressed tiles, and are compressed without interruptions. If you were playing music before this, it would freeze, which is clearly notable in Selbi's Sonic Erazor hack. As you can hear, it takes actually pretty long time, and for not very huge save of ROM space. If we uncompress the tiles, it will be able to load in only few frames, meaning the music will not be interrupted much at all. So, it obviously is quite a good speed up considering the space usage wont be much bigger, it's good tradeoff for the speed. You will need uncompressed tile-loading code from the misc section.

You want to go to each instance of this code:

Code (ASM):

1.         move.l  #$70000002,($C00004).l
2.         lea (Nem_TitleCard).l,a0 ; load title card patterns
3.         bsr.w   NemDec

And, you want to replace it with:

Code (ASM):

1.         move.l  #$70000002,($C00004)        ; set mode "VRAM Write to $B000"
2.         lea Nem_TitleCard,a0        ; load title card patterns
3.         move.l  #((Nem_TitleCard_End-Nem_TitleCard)/32)-1,d0; the title card art lenght, in tiles
4.         jsr LoadUncArt          ; load uncompressed art

You can find there ins lables loc_37B6:, loc_47D4:, and Cont_ClrObjRam:. Next, decompress artnem/ttlcards.bin. You can change the filepath of this file, rename, etc., it's up to you. However in this example I am going to keep it as is. Now, go to lable Nem_TitleCard:, and you should see something like this:

Code (ASM):

1. ; ---------------------------------------------------------------------------
2. ; Compressed graphics - various
3. ; ---------------------------------------------------------------------------
4. Nem_TitleCard:  incbin  artnem\ttlcards.bin ; title cards
5.         even

You want to change it to this:

Code (ASM):

1. ; ---------------------------------------------------------------------------
2. ; Compressed graphics - various
3. ; ---------------------------------------------------------------------------
4. Nem_TitleCard:      incbin  artnem\ttlcards.bin ; title cards
5. Nem_TitleCard_End:  even

Next, lets fix the result screens, which would cause crash. At GotThroughAct:, replace:

Code (ASM):

1.         moveq   #$10,d0
2.         jsr (LoadPLC2).l    ; load title card patterns

with:

Code (ASM):

1.         move.l  a0,-(sp)            ; save object address to stack
2.         move.l  #$70000002,($C00004)        ; set mode "VRAM Write to $B000"
3.         lea Nem_TitleCard,a0        ; load title card patterns
4.         move.l  #((Nem_TitleCard_End-Nem_TitleCard)/32)-1,d0; the title card art lenght, in tiles
5.         jsr LoadUncArt          ; load uncompressed art
6.         move.l  (sp)+,a0            ; get object address from stack

And there you have it! Enjoy the speed!

Method 2: Comper compressed level graphics

Spoiler

Extra ROM usage: ~ 10800 bytes
Extra RAM usage: 0
Optimization level: Good

Another long process is to load level graphics. While the processor does other things while that, it must wait for it before fading level in because of the PLC queue, and the fact that the graphics would look terrible (glitched graphics, blank space, etc.). However, because of how fast comper is, we can highly optimize the loading even if we reserve the processor completely just to load level graphics. However Comper isn't as compact as Nemesis compression, so extra space usage in inevitable. It'd be almost impossible to calculate exact space usage, so I threw an aproximation. The space usage may vary. It is good to note that currently no level editor supports Comper, so you must recompress if you wish to edit this system. You will need comper compressed tile-loading code from the misc section.

So, what you want to do first, is recompress these files from Nemesis to Comper:

artnem/8x8ghz1.bin
artnem/8x8ghz2.bin (if you have combined these files, then obviously recompress the combined file)
artnem/8x8lz.bin
artnem/8x8mz.bin
artnem/8x8sbz.bin
artnem/8x8slz.bin
artnem/8x8syz.bin

Next, go to MainLoadBlockLoad:, and replace this

Code (ASM):

1.         moveq   #0,d0
2.         move.b  ($FFFFFE10).w,d0
3.         lsl.w   #4,d0
4.         lea (MainLoadBlocks).l,a2

with

Code (ASM):

1.         moveq   #0,d0           ; quickly clear d0
2.         move.b  ($FFFFFE10).w,d0    ; get level ID
3.         bsr.s   LoadLevelArt        ; load level tiles
4.         lsl.w   #4,d0           ; shift level ID left by 4 bits
5.         lea (MainLoadBlocks).l,a2

Somewhere near MainLoadBlockLoad:, insert thise code (For not combined GHZ art files):

Code (ASM):

1. ; ---------------------------------------------------------------------------
2. ; Subroutine to load level art patterns
3. ; ---------------------------------------------------------------------------
4.  
5. ; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
6. LoadLevelArt:
7.         move.w  d0,-(sp)        ; store level ID to stack
8.         lsl.w   #2,d0           ; shift 2 bits left
9.         move.l  LLA_ArtList(pc,d0.w),a0 ; get correct entry from art file list
10.         move.l  #$40000000,d4       ; set "VRAM Write to $0000"
11.         bsr.w   LoadCompArt     ; load comper compressed art
12.  
13.                 ; workaround for GHZ's secondary art
14.         cmpi.b  #0,ZoneID.w     ; is GHZ?
15.         bne.s   LLA_End         ; if not, don't load art
16.                 lea Nem_GHZ_2nd,a0      ; get GHZ 2nd patterns
17.         move.l  #$79A00000,d4       ; set "VRAM Write to $39A0"
18.         bsr.w   LoadCompArt     ; load comper compressed art
19.  
20. LLA_End:
21.         move.w  (sp)+,d0        ; get old level ID from stack again
22.         rts             ; return to subroutine
23.  
24.         ; list of art patterns used in levels
25. LLA_ArtList:    dc.l Nem_GHZ_1st, Nem_LZ, Nem_MZ, Nem_SLZ, Nem_SYZ, Nem_SBZ

(for combined GHZ art files)

Code (ASM):

1. ; ---------------------------------------------------------------------------
2. ; Subroutine to load level art patterns
3. ; ---------------------------------------------------------------------------
4.  
5. ; ||||||||||||||| S U B R O U T I N E |||||||||||||||||||||||||||||||||||||||
6. LoadLevelArt:
7.         move.w  d0,-(sp)        ; store level ID to stack
8.         lsl.w   #2,d0           ; shift 2 bits left
9.         move.l  LLA_ArtList(pc,d0.w),a0 ; get correct entry from art file list
10.  
11.         move.l  #$40000000,d4       ; set "VRAM Write to $0000"
12.         bsr.w   LoadCompArt     ; load comper compressed art
13.         move.w  (sp)+,d0        ; get old level ID from stack again
14.         rts             ; return to subroutine
15.  
16.         ; list of art patterns used in levels
17. LLA_ArtList:    dc.l Nem_GHZ, Nem_LZ, Nem_MZ, Nem_SLZ, Nem_SYZ, Nem_SBZ

Next, we need to remove pointers for level art from _inc/Pattern load cues.asm. The pointers exist for all levels, and here is example how to do it for LZ. Originally you see this:

Code (ASM):

1. ; ---------------------------------------------------------------------------
2. ; Pattern load cues - Labyrinth
3. ; ---------------------------------------------------------------------------
4. PLC_LZ:     dc.w $B
5.         dc.l Nem_LZ     ; LZ main patterns
6.         dc.w 0
7.         dc.l Nem_LzBlock1   ; block
8.         dc.w $3C00
9.         dc.l Nem_LzBlock2   ; blocks
10.         dc.w $3E00
11.         ...

You want to change it to:

Code (ASM):

1. ; ---------------------------------------------------------------------------
2. ; Pattern load cues - Labyrinth
3. ; ---------------------------------------------------------------------------
4. PLC_LZ:     dc.w $A
5.         dc.l Nem_LzBlock1   ; block
6.         dc.w $3C00
7.         dc.l Nem_LzBlock2   ; blocks
8.         dc.w $3E00
9.         ...

Note how I reduced the value in the first dc.w as well? This is the pointer for the amount of PLC's to load, and since we removed the main art file, that is one less. You want to repeat this for all of the levels.

Method 3: Not waiting for PLC's being loaded

Spoiler

Extra ROM usage: less than 100 bytes
Extra RAM usage: 48 (0x30) bytes
Optimization level: Great

Note: You are required to have implented Method 2: Comper compressed level graphics in order to make this work correctly.
In the original game, the level loading hangs for few seconds while it loads level graphics, such as badniks and actual level tiles. This is necessary to not make the level look broken. However as we implented level graphics being decompressed with Comper, therefore it is not an issue, and you can load other graphics much faster, for example while the title card sequence is running. This means, we don't have to wait any graphics to load before we can let the player move already, and they will never notice. However, in order to store more PLC's in the queue, you need to allocate more RAM. We will extend the PLC queue from $FFFFF680-$FFFFF6FF to $FFFFF650-$FFFFF6FF. So first of all, we need to move SBZ and LZ palette cycle pointers from $FFFFF650-$FFFFF661 to somewhere else. You need to find $11 bytes of free RAM somewhere, for this example, I will use $FFFFFECA-$FFFFFEDB.
Go to loc_19F0:, loc_1A0A:, and loc_1ADA:, and replace each instance of $FFFFF650 with your desired RAM address. In my case, $FFFFFECA.
Before StartOfROM:, place these equates:

Code (ASM):

1. PLCQueueAdr: =  $FFFFF650   ; beginning of RAM allocated for PLC
2. PLCQueue: = PLCQueueAdr+4   ; start of PLC queue
3. PLCQueueEnd: =  $FFFFF700-$20   ; end of PLC queue, start of equates for PLC, for example last state of Nemesis decompression

Got to ClearPLC, and replace:

Code (ASM):

1.         moveq   #$1F,d0

with:

Code (ASM):

1.         moveq   #(((PLCQueueEnd+$20)-PLCQueueAdr)/4)-1,d0   ; lenght of the PLC RAM

Next, in loc_16DC:, replace:

Code (ASM):

1.         moveq   #$15,d0

with:

Code (ASM):

1.         moveq   #((PLCQueueEnd-4-PLCQueue)/4)-1,d0  ; lenght of the PLC queue RAM

Above Level_ClrVars: and End_ClrRam: replace

Code (ASM):

1.         move.w  #$15,d1

with:

Code (ASM):

1.         move.w  #((PLCQueueAdr-$FFFFF628)/4)-1,d1

These make sure the lenght of the transfers are correct, and so PLC works as it should. Next up, we should fix the PLC addresses. Replace each instance of ($FFFFF680).w with PLCQueueAdr.w, and each instance of ($FFFFF684).w with PLCQueue.w. Now we have successfully extended PLC queue! Next, we need to make use of this extra space. So, go to Level_TtlCard:, and you should see something like this:

Code (ASM):

1.         move.b  #$34,($FFFFD080).w ; load title card object
2.  
3. Level_TtlCard:
4.         move.b  #$C,($FFFFF62A).w
5.         bsr.w   DelayProgram
6.         jsr ObjectsLoad
7.         jsr BuildSprites
8.         bsr.w   RunPLC_RAM
9.         move.w  ($FFFFD108).w,d0
10.         cmp.w   ($FFFFD130).w,d0 ; has title card sequence finished?
11.         bne.s   Level_TtlCard   ; if not, branch
12.         tst.l   ($FFFFF680).w   ; are there any items in the pattern load cue?
13.         bne.s   Level_TtlCard   ; if yes, branch
14.         jsr Hud_Base

Replace it with this:

Code (ASM):

1.         move.b  #$34,($FFFFD080).w  ; load title    card object
2.         move.w  #3,$FFFFFE04.w      ; set the timer (Fixes Title card bug)
3.  
4. Level_TtlCard:
5.         move.b  #$C,($FFFFF62A).w   ; set VBlank routine to $C (loads more tiles per VBlank thank 8 which is normally used)
6.         bsr.w   DelayProgram        ; wait for VBlank
7.         jsr ObjectsLoad     ; run object code
8.         jsr BuildSprites        ; display sprites
9.         bsr.w   RunPLC_RAM      ; put PLC data to RAM
10.  
11.         move.w  ($FFFFD100+8).w,d0
12.         cmp.w   ($FFFFD100+$30).w,d0    ; has title card sequence finished?
13.         bne.s   Level_TtlCard       ; if not, branch
14.  
15.         move.w  ($FFFFD0C0+8).w,d0  ; fix for FZ crash and title card issue
16.         cmp.w   ($FFFFD0C0+$30).w,d0    ; has title card sequence finished?
17.         bne.s   Level_TtlCard       ; if not, branch
18.  
19.         subi.w  #1,$FFFFFE04.w      ; substract 1 from timer
20.         bne.s   Level_TtlCard       ; if timer is not 0, branch
21.         jsr Hud_Base

If some of the levels crash, you can adjust the value 3 in the second line to bigger value, until the levels don't crash. However this works completely in vanilla Sonic 1. EHowever, there is still a slight possibility that FZ can cause some issues, so lets quickly fix that. Go to Resize_FZmain:, and change:

Code (ASM):

1.         bsr.w   LoadPLC     ; load FZ boss patterns

to

Code (ASM):

1.         bsr.w   LoadPLC2    ; load FZ boss patterns

Never mind the above, doing the change will make the explosion graphics break, and you can not cause any crashes in the origianl game anyway, so there is no good reason to do that chance
And there you have it!

Misc

Spoiler

comper compressed tile-loading

Spoiler

This is the piece of code needed for parts of this tutorial; You will be informed whenever this is necessary.
Right above LoadPLC:, put this piece of code:

Code (ASM):

1. ; ===============================================================
2. ; ---------------------------------------------------------------
3. ; COMPER compressed art to VRAM loader
4. ; ---------------------------------------------------------------
5. ; INPUT:
6. ;       a0      - Source Offset
7. ;   d4  - VDP mode
8. ; ---------------------------------------------------------------
9. LoadCompArt:
10.         lea $FF0000.l,a1    ; get address of compdec buffer
11.         bsr.s   CompDec     ; decompress art
12.  
13.         lea $FF0000.l,a3    ; get address of compdec buffer again
14.         lea $C00000.l,a6    ; get VDP data port
15.  
16.         move.l  a1,d0       ; move end address to d0
17.         sub.l   a3,d0       ; substract the compdec buffer address from d0
18.         lsr.l   #2,d0       ; shift 2 bits to right (as we transfer longword per loop)
19.         subq.l  #1,d0       ; substract 1 from d0 because of dbf
20.  
21.                 move    #$2700,sr   ; disable interrupts
22.         move.l  d4,4(a6)    ; set VDP transfer mode
23.  
24. @loop       move.l  (a3)+,(a6)  ; transfer next longword
25.         dbf d0,@loop    ; loop until d0 = 0
26.         move    #$2300,sr   ; enable interrupts
27.         rts
28.  
29. ; ===============================================================
30. ; ---------------------------------------------------------------
31. ; COMPER Decompressor
32. ; ---------------------------------------------------------------
33. ; INPUT:
34. ;       a0      - Source Offset
35. ;       a1      - Destination Offset
36. ;
37. ;  Full credits of this to Vladikcomper
38. ; ---------------------------------------------------------------
39.  
40. CompDec:
41. @newblock
42.         move.w  (a0)+,d0                ; fetch description field
43.         moveq   #15,d3                  ; set bits counter to 16
44.  
45. @mainloop
46.         add.w   d0,d0                   ; roll description field
47.         bcs.s   @flag                   ; if a flag issued, branch
48.         move.w  (a0)+,(a1)+             ; otherwise, do uncompressed data
49.         dbf     d3,@mainloop            ; if bits counter remains, parse the next word
50.         bra.s   @newblock               ; start a new block
51.  
52. ; ---------------------------------------------------------------
53. @flag   moveq   #-1,d1                  ; init displacement
54.         move.b  (a0)+,d1                ; load displacement
55.         add.w   d1,d1
56.         moveq   #0,d2                   ; init copy count
57.         move.b  (a0)+,d2                ; load copy length
58.         beq.s   @end                    ; if zero, branch
59.         lea     (a1,d1),a3              ; load start copy address
60.  
61. @loop   move.w  (a3)+,(a1)+             ; copy given sequence
62.         dbf     d2,@loop                ; repeat
63.         dbf     d3,@mainloop            ; if bits counter remains, parse the next word
64.         bra.s   @newblock               ; start a new block
65.  
66. @end    rts
67.  

If you already had CompDec routine, you can remove the old one (or the new one, they are the same anyway).

uncompressed tile-loading

Spoiler

This is the piece of code needed for parts of this tutorial; You will be informed whenever this is necessary.
Right above LoadPLC:, put this piece of code:

Code (ASM):

1. ; ===============================================================
2. ; ---------------------------------------------------------------
3. ; uncompressed art to VRAM loader
4. ; ---------------------------------------------------------------
5. ; INPUT:
6. ;       a0      - Source Offset
7. ;   d0  - length in tiles
8. ; ---------------------------------------------------------------
9. LoadUncArt:
10.         move    #$2700,sr   ; disable interrupts
11.         lea $C00000.l,a6    ; get VDP data port
12.  
13. LoadArt_Loop:
14.         move.l  (a0)+,(a6)  ; transfer 4 bytes
15.         move.l  (a0)+,(a6)  ; transfer 4 more bytes
16.         move.l  (a0)+,(a6)  ; and so on and so forth
17.         move.l  (a0)+,(a6)  ;
18.         move.l  (a0)+,(a6)  ;
19.         move.l  (a0)+,(a6)  ;
20.         move.l  (a0)+,(a6)  ; in total transfer 32 bytes
21.         move.l  (a0)+,(a6)  ; which is 1 full tile
22.  
23.         dbf d0, LoadArt_Loop; loop until d0 = 0
24.         move    #$2300,sr   ; enable interrupts
25.         rts

If you find any bugs, or have other suggestions, post them in the comments!

 

I actually was going to do that, but completely forgot. I had done this before, by setting the level restart flag to 2 instead of 1. However I need to check very closely that I don't make the code a bloated mess while doing it, so I'll look into it later. Thanks for the suggestion anyway

 

Hi!

 

Yeah I don't think enough to be worth making a tutorial on.

Also, I updated the post with some fixes and edits.

 

I noticed HUD numbers not loading while testing as well, but I fixed it by extending the delay above Level_TtlCard: by few frames. I am not entirely sure as to why it happens, but I'll get to it soon.