LFS Forum - Insim: Flags + replayspeed

#1 - abz1

Insim: Flags + replayspeed

Thu 2 Feb 2006, 21:32

Ive made some pretty good progress using java. Im just creating classes for each packet received. So I am doing the STA packet at the moment.

1. so, im trying to convert the replayspeed into a float value, im using the 4 bytes which i got from the array sent from LFS (check attached file to see data) and stored them into a seperate array



import java.nio.*;
    public static void main(String args[])
    {
      byte [] a = new byte[4];
      a[0] = 0;
      a[1] =0;
      a[2] =-128;
      a[3]=63;

      ByteBuffer b= ByteBuffer.allocate(a.length);
      b.put(a);

      Float f = (float)b.getFloat(0);
      int fe = f.intValue();

     System.out.println(f);
     System.out.println(fe);      
    }

I dont know if the conversion is correct and this is the output i get
f= 4.6006E-41
fe=0

2. and finally can someone explain how the values can be extracted from the flags


    ISS_GAME            1    // in game (or MPR)
    ISS_REPLAY            2    // in SPR
    ISS_PAUSED            4    // paused
    ISS_SHIFTU            8    // in SHIFT+U mode
    ISS_SHIFTU_HIGH        16    // HIGH view
    ISS_SHIFTU_FOLLOW    32    // following car
etc.

so i receive these values
FLAG
-32
12
from lfs what does it mean(what flags does it contain)

Attached files

#2 - Stuff

Fri 3 Feb 2006, 00:04

The way I check if those flags are set is to simply 'and' the value to the word and if it equals the value, the flag is set. Eg.

If(flags And ISS_SHIFTU == ISS_SHIFTU)
{
//Shift+U flag is set
}

Not too familiar with Java but you get the picture

#3 - the_angry_angel

Fri 3 Feb 2006, 09:20

Basically the incoming variable has multiple settings symultaneously, which you need to extra using bitwise operations.

The reason for this is that the "replay speed" could be both ISS_PAUSED and ISS_SHIFTU_HIGH, and you dont want to use multiple variables to store that 1 item of data, as it is a waste of memory.

As RayOK has said, using the bitwise operator AND allows you to check if its set or not.

If you want to learn more on Bitwise Operations, check out this article at GameDev. I always found it to be the best article on the subject.

#4 - Messiah

Fri 3 Feb 2006, 09:40

Quote from abz1 :1. so, im trying to convert the replayspeed into a float value, im using the 4 bytes which i got from the array sent from LFS (check attached file to see data) and stored them into a seperate array

So.. I finally have to admin that I don't know how to convert an array of bytes into a float value (yet), hehe. But there's 2 things confusing me.

I'm using C#, very similar to Java.

1) You have a byte value of -128. Isn't the datatype "byte" also a non-signed numeric datatype in Java? That means it cannot hold negative values? If so casting -128 (as integer) to a (byte) will make it 128 (positive).

2) In LFS.Live I'm often using the "BitConverter" class. Maybe you have this in Java as well and "float" is probably called "single" as well as in C#. I don't have the ToFloat() available on a (byte-)array for example. Maybe lets change the negative sign from your -128 and it turns out to be 1.0 as result as well.

After all, the following code gives me 1.0f as output:

                byte[] value = new byte[] { 0, 0, 128, 63 };
                float floatValue = BitConverter.ToSingle(value, 0);
                
                Console.WriteLine("Float conversion: {0}", floatValue);

Method explained:
Returns a single-precision floating point number from four bytes at a specified position in a byte array.
BitConverter.ToSingle(byte[] array, int startIndex).

#5 - abz1

Sun 5 Feb 2006, 20:03

the float problem has been solved, just the flags left. So am i right in doing this. converting the 2 bytes received from the array into a unsigned byte and then adding them togther to carry out the bitwise operation?

say you get the flags -32 12 two bytes
I will then pass both bytes into this method


    public static int getInt(byte b)
    {
       return b & 0xFF;
    }

and get 224 and 12 add them and they equal 236 then use the bitwise operation on this value.