Turrican (128K)

[Jean-Marie]

While I'm not a fan of this new palette, if many people request it then Vox populi, vox Dei.
Now, there are also people who will prefer the regular one. So maybe a poll should be taken?

[eto]

So maybe a poll should be taken?

or just an option when starting the game? Not sure if that's feasible.

[Jean-Marie]

or just an option when starting the game?

Yeah, I guess I could include alternate Levels A,B & C with a new palette, since only the first 3 levels are concerned. I will check this out; for the moment I'm struggling to find 100 bytes free to make the Spikes work with Axelay's optimized scrolling!

[dodogildo]

or just an option when starting the game? Not sure if that's feasible.

That would be great, for the new palette.

[Jean-Marie]

The spikes are working too. Now, I'll see if I can tidy up the code, and next week I'll try to write the changes in the Level A file, which should be very challenging.

[lightforce6128]

next week I'll try to write the changes in the Level A file, which should be very challenging.

Hopefully it will not be challenging. For compression you can use any language, and modern computers will process the data in any language (also slow scripting languages) more than fast enough.

Whenever you find a sequence of the same byte A of length N, replace it with these four bytes: A,N,#A5,#CC. Only apply this if the sequence is longer than 4 bytes. That's all. This is not the best compression, but a fast one that will work acceptably on sprites and level maps with much background.

Example:

"1,2,3,4,  a,a,a,a,a,a  ,5,6,7,8"  gets  "1,2,3,4,  a,6,#A5,#CC  ,5,6,7,8" (spaces only for better readability)

Hopefully the used escape sequence #A5,#CC is not used anywhere in the data to compress. If it is, either the escape sequence can be changed to something else, or it has to be encoded as sequence of length 1 (what will cost 3 bytes):

Example:
"1,2,3,  #A5,#CC  ,4,5,6"  gets  "1,2,3,  #A5,1,#A5,#CC,  #CC  ,4,5,6" (replace the #A5 with a sequence of length 1)


Two questions remain:

• Where should the file be loaded? Usually at the begin of the buffer that will contain the uncompressed data later.
• And which routine says the decompressor where the compressed data is located? Needed are begin and end of the data.

[Jean-Marie]

I think the real difficulties will come with the levels where Parallax is used. Daren used animated tiles to create the effect, where background tiles are "slided" in the Tile Map. This is quite ingenious.
Level I (4.1) looks like a real nightmare with a slew of animated tiles (not only for the parallax).
It's quite easy to carry out LDI/LDD instructions on some linear memory, but with Axelay's optimization, the tiles offsets become shuffled, and that makes thing more complex and lengthy 

 

Code Select Expand

;;TURRICAN.LVI

org &1b78
ld ix,&1d07
ld b,&0f
ld a,(&c7f3)
ld c,a
l1b82:
ld l,(ix)
ld h,(ix+1)
ld a,l
cp &20
jp nc,l1ba6
bit 0,c
jp z,l1b94
inc h
l1b94:
bit 1,c
jp z,l1b9a
dec l
l1b9a:
bit 2,c
jp z,l1ba0
dec h
l1ba0:
bit 3,c
jp z,l1ba6
inc l
l1ba6:
ld (ix),l
ld (ix+1),h
inc ixl
inc ixl
djnz l1b82
ld a,(&c7f3)
rra
jp nc,l1bfc
ld de,&1920
ld hl,&6cb0
REPEAT 8:ldi:ENDM
ld de,&6cb0
call @LDIR-24-24
ld hl,&1920
REPEAT 8:ldi:ENDM
ex de,hl
ld e,&20
call @LDIR-8-8
ld de,&6cd0
call @LDIR-24-24
ld hl,&1920
call @LDIR-8-8
l1bfc:
ld a,(&c7f3)
bit 1,a
jp z,l1c28
ld ix,&6cb0
ld b,&10
l1c0a:
ld e,(ix)
ld d,(ix+1)
ld l,(ix+&20)
ld h,(ix+&21)
ld (ix),h
ld (ix+1),e
ld (ix+&20),d
ld (ix+&21),l
inc ixl
inc ixl
djnz l1c0a
l1c28:
ld a,(&c7f3)
bit 2,a
jp z,l1c72
ld de,&1920
ld hl,&6cc8
REPEAT 8:ldi:ENDM
ld de,&6ccf
ld l,&c7
call @LDDR-24-24
ld e,&b0
ld hl,&1920
REPEAT 8:ldi:ENDM
ex de,hl
ld e,&20
ld l,&e8
call @LDIR-8-8
ld de,&6cef
ld l,&e7
call @LDDR-24-24
ld e,&d0
ld hl,&1920
call @LDIR-8-8
l1c72:
ld a,(&c7f3)
bit 3,a
jp z,l1c9e
ld ix,&6cb0
ld b,&10
l1c80:
ld e,(ix)
ld d,(ix+1)
ld l,(ix+&20)
ld h,(ix+&21)
ld (ix),d
ld (ix+1),l
ld (ix+&20),h
ld (ix+&21),e
inc ixl
inc ixl
djnz l1c80
l1c9e:
ld a,(&dea0)
ld hl,&3e15
rra
jp c,l1cac
ld l,&55
l1cac:
ld de,&6c00
call @LDIR-64-64
ld ix,(&6c7e)
ld iy,(&6c7c)
ld e,&7f
ld hl,&6c7b
call @LDDR-60-60
ld (&6c42),iy
ld (&6c40),ix
ld hl,&6be0
ld de,&1920
call @LDIR-16-16
ld a,(&dea0)
rra
ret c
ld de,&6be0
call l1cef
ld hl,&1920
l1cef:
ld b,&08
l1cf1:
ld c,(hl)
inc l
ld a,(hl)
inc l
exx
ld b,&87
ld c,a
ld a,(bc)
exx
ld (de),a
inc e
ld a,c
exx
ld c,a
ld a,(bc)
exx
ld (de),a
inc e
djnz l1cf1
ret
REPEAT 9:rst 0:ENDM

ORG &9D80
REPEAT 95:ldi:ENDM
@LDIR:
ret

ORG &9E40
REPEAT 95:ldd:ENDM
@LDDR:
ret


[lightforce6128]

I think the real difficulties will come with the levels where Parallax is used. Daren used animated tiles to create the effect, where background tiles are "slided" in the Tile Map. This is quite ingenious. Level I (4.1) looks like a real nightmare with a slew of animated tiles (not only for the parallax).

When I first saw this, I was really impressed. Paralax scrolling was not really common for the CPC. Until recently I thought it would use some kind of optical illusion, where the tiles contain the same background, but shifted differently then the tile offset. But this could not be used here, because it would interfere with reusing tiles throughout a level.

I did some further analysis and now have a better understanding about how the drawing works. There are three levels of image generation, not two!

• The map of e.g. size 137x51 contains indices of blocks (not of tiles!).
• There are 256 blocks, each containing 4x4 tile indices.
• Finally there are 256 tiles, each containing 4x8 pixels.

With this trick the game achieves a compression ratio of 118:1 (or reduces the size by 99.2%). The drawn map has a size of 2192x1632 or 3.6 megapixel, while the three data structures only need 14.8 kilobytes.

By looking at tiles and blocks of level I (4.1) I found there are several blocks showing paralax background. But there are only four tiles (index 203 to 206). The whole paralax scrolling magic is done only in these four tiles!

[lightforce6128]

For better visualization I append the map, blocks, and tiles of level A (1.1). I suppose this is not a big spoiler because almost everybody will know level 1.1 more than good enough.