I had discovered the compress and decompress algorithm of *.img file by decompile landgen.exe using IDA+HexRays Decompiler.

These are decompress codes:
Private Sub DecompressTest(lpbm() As Byte, lpbuf() As Byte)
On Error GoTo a
Dim v5 As Long 'repeat count
Dim nbm As Long 'lpbm
Dim nbuf As Long 'lpbuf
Dim nOffset As Long
'////////////////compress format
'////////////////1 byte:
'0xxxxxxx
'x=color=0-127
'////////////////2-byte: repeat=3-17
'1rrrrooo oooooooo
'r+2=repeat
'o+1=offset=1-&h800&
'////////////////3-byte: repeat=18-273
'10000ooo oooooooo rrrrrrrr
'r+18=repeat
'o=offset=1-&h7ff&
'////////////////2 byte: EOF
'10000000 00000000=&h80 &h00
Do
Do
Do
v5 = lpbuf(nbuf)
If v5 And &H80& Then Exit Do
lpbm(nbm) = v5 'm_clrs(v5)
nbuf = nbuf + 1
nbm = nbm + 1
Loop
nOffset = (v5 * 256& + lpbuf(nbuf + 1)) And &H7FF&
v5 = (v5 \ 8&) And &HF&
If v5 = 0 Then Exit Do
nOffset = nOffset + 1
v5 = v5 + 2
Do
lpbm(nbm) = lpbm(nbm - nOffset)
nbm = nbm + 1
v5 = v5 - 1
Loop While v5
nbuf = nbuf + 2
Loop
If nOffset = 0 Then Exit Do
v5 = lpbuf(nbuf + 2) + 18&
Do
lpbm(nbm) = lpbm(nbm - nOffset)
nbm = nbm + 1
v5 = v5 - 1
Loop While v5
nbuf = nbuf + 3
Loop
Exit Sub
a:
MsgBox "Error in decompressing data!", vbExclamation
End Sub

and the compress algorithm:

thx. but what language is that code written in?

Looks like Visual Basic.

Looks like Visual Basic.
it's completely unreadable for me.
acme, could you translate it into pseudocode / C?

I'm fairly fluent with Visual Basic, but I'm also having a hard time understanding what you are doing here. Could you please add some code comments or possibly a working example of compression and decompression?

first. I hate Visual Basic sintax.
second. why the hell do you use loops where humans use if statements??

I'll post a C version of the decompression algorithm, but anyway, the offset that you get from the 3 or 2 bytes command (let's call it coff), and off is the index of the next byte to be written in the output buffer (out[]), and i is the number of iterations:
for(;i>0;i--)
out[off]=out[off++-coff];
looks strange.

EDIT:
Etho, I hope that this java code is readable for you (inf is a stream of bytes)

String decode() throws IOException {
//[...]
int cmd;
int next=0; //offset of next write
while((cmd=inf.read())!=-1){ //read a byte
if((cmd&0x80)==0) //command: 1 byte (color)
imgData[next++]=(byte) cmd;
else{
int arg1=(cmd>>3)&0xF, //arg1=bits 2-5
arg2=inf.read();
if(arg2==-1)
return "not enough data";
arg2=((cmd<<8)|arg2)&0x7FF; //arg2=bits 6-16
if(arg1==0){
if(arg2==0) //command: 0x80 0x00
return null;
int arg3=inf.read();
if(arg3==-1)
return "not enough data";
next=copyData(next,arg2,arg3+18); //command: 3 bytes
}
else
next=copyData(next,arg2+1,arg1+2); //command: 2 bytes
}
}
if(next!=imgData.length)
return "not enough data";
return null;
}

int copyData(int offset,int coffset,int rep){
for(;rep>0;rep--)
imgData[offset]=imgData[offset++-coffset];
return offset;
}
damn, no indexing...

I'm going to test this soon

good job acme_pjz, your algorithm works perfectly! I could write a IMG converter, from compressed to uncompressed format, and the result is identical to W:A decompression

It works? That's great. I know a few people, myself included, who could have really used this information a few years ago. It still has potential to be very useful, it's just that the number of 3rd party programmers for Worms has dwindled a lot.

But anyways... who's going to make the first W:A mission editor?

But anyways... who's going to make the first W:A mission editor?
There already is one, The Fiddler. But as you know, it is 3.0 only.

It works? That's great. I know a few people, myself included, who could have really used this information a few years ago. It still has potential to be very useful, it's just that the number of 3rd party programmers for Worms has dwindled a lot.

But anyways... who's going to make the first W:A mission editor?

I see that the img format is optimized for default sized maps.

well, probably next RubberWorm will be able to set events and sequences online,and other settings from wam files.

Thanks for the Interactive Disassembler and Hex-Rays Decompiler... make it possible to decompile the landgen.exe assembler to C-like pseudocode.

There is just a problem that my compress algorithm is not very good... the compressed file is usually a bit bigger then the original one...

why the hell do you use loops where humans use if statements??The decompiled code is exactly three loops...

why the hell do you use loops where humans use if statements??oh right, decompiler isn't human:p

HAHA ;D :D :) :lol