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Random number problem!

General and Gameplay Programming Programming

Started by iwoplaza June 19, 2012 02:53 PM

4 comments, last by tanzanite7 11 years, 10 months ago

iwoplaza

174

Author

June 19, 2012 02:53 PM

I'm making three-dimensional application in OpenGL, which generates a random blocks in the world (something like Minecraft). This is my script to generate blocks:



void GenBlocks(){

	 int currblock;

	 int currXline;

	 int currZline;

	 int randID;

	 for(currblock = 0,currXline = 1,currZline = 1;currblock < blockAM;currblock++,currXline++){

		   randID = rand() % 2 + 1;

		   if(currXline > pierw(blockAM)){

			  currXline = 1;

			  currZline++;

		   }

		   block[currblock].x = currXline*3;

		   block[currblock].y = 0;

		   block[currblock].z = currZline*3;

		   block[currblock].id = randID;

	 }

}

But every time when I run the application, it generates the same!

Thanks in advance.

fastcall22

10,918

June 19, 2012 03:21 PM

You need to seed the random number generator when the program starts.

szecs

2,990

June 19, 2012 03:24 PM

Random number generators aren't really random.
That means they use some calculations, pre-defined arrays of pseudo-random numbers, whatever, you get the idea.
Every random number generators have a "randomize" function of some sorts, for example "srand". They take an initial value, often called as "seed". Using he same seed value will produce exactly the same sequence of numbers. If you don't call this initial srand, the generator will use a default seed I guess.

So, you need to call srand and pass a number to it. You would probably ask what can you use as seed, if you can't use a really random number in the first place.
Usually, system time is used for that, since it's in milliseconds and ever growing.
(what's cool about this thing is that if you save then load the seed number, you can regenerate exactly the same world from only an[color=#0000ff] int. As you have it now.)

I'm ninja'd.