Pfhreak posted:

Now I tend to start with small goals in mind -- get the player moving, get the camera panning, add an inventory, how about bad guys, etc. I tackle that one problem in code with little planning.

Zhentar posted:

In this context, "seed" is short for "random seed". The whole point of entering the seed is that exactly the same "random" numbers will come up when you use it.

HaB posted:

Yeah I know. What I mean is, Minecraft is using that seed in some equation that sets the spawn point. I'm trying to see if anyone knows what that equation is.

HaB posted:

So...does anyone know what method it's using to choose? Thanks in advance.

ShoulderDaemon posted:

It is as you described. Minecraft picks a random point within a few hundred blocks of (0,0) until it finds one that's an acceptable spawn location.

HaB posted:

If it's random, then it wouldn't be the same every time the same seed is used. That's what I'm saying. Here's a test to prove it:

HaB posted:

If it's random, then it wouldn't be the same every time the same seed is used.

Orzo posted:

I'm not sure I follow. The algorithm which generates worlds is using a random number generator with a seed. The algorithm which places the player is using the same seed. So it appears 'random', although it is deterministic when you give it a certain seed. As for what the algorithm is, you'd need the source code.

MonsterUnderYourBed posted:

There is a minecraft modding thread in Games which would probably be more able to answer your question.

HaB posted:

Yeah I know. What I mean is, Minecraft is using that seed in some equation that sets the spawn point. I'm trying to see if anyone knows what that equation is.

Zhentar posted:

The "equation" is a psuedo random number generation algorithm. To determine the output of a specific call, you need to know not only the algorithm, but the position in the sequence. If the worldgen process always performs exactly the same number of random calls before that point, then you'd just need to figure that, say, the 127,403rd time random() gets called it's to pick the spawn point. However, I would assume that the worldgen process also involves testing and rejecting candidates, in which case the position would be variable. You'd likely have to perform most of the worldgen process to determine what the random value used to pick the spawn point is.

Serenade posted:

I've heard several times that the best way to get better at a craft is to practice it every day. I was wondering how one could apply this to game design.

The answer of 'make a game every day' seems like an unreasonable starting point. Simply writing down game mechanics in a notebook doesn't seem the same taking an idea and putting it into practice.

Nippashish posted:

How about working on a game every day? Sounds pretty simple to me.

Do you think authors write a new book every day? How about an architect designing a new building every day? A composer writing a new symphony every day? A developer (of any sort) building a new application every day?

What I'm trying to say is you should think about what that adage means before you try to put it into practice. There are very few things in life worth doing that can be done in a day.

HaB posted:

If it's random, then it wouldn't be the same every time the same seed is used. That's what I'm saying. Here's a test to prove it:

Load Minecraft.
Create a New World, Select More World Options
Enter 1 as the seed
Create World
when it loads, don't move and hit f3 to look at your coordinates.
You are standing at: (251.5, 65.6, 232.5)

If it's random, then how do I know where YOU are standing?

It's based on the world seed. I'm trying to figure out HOW.

Smug guy posted:

Jeez, guys. I know how pseudorandom number generators work!

Vinterstum posted:

1. Figure out the simplest thing you can possibly put on screen, as your first step.
2. Code it the simplest and most straightforward way you can imagine. Plan nothing ahead.
3. Figure out what the next logical step is, which gives you a sense of visual progress (i.e. your game is getting somewhere, not your code).
4. Refactor existing code if needed (do not skip this), and then implement that step the simplest way you can.
5. Goto 3.

Done.

Pfhreak posted:

Clearly this is not the case.

westborn posted:

Could you people get of your high horses for a second and actually read his initial question. He clearly does know how the seed for the terrain generation works. He was asking how the spawnpoint is determined afterwards, as Minecraft has/had the tendency to not always spawn you at the same point on the same seed.
That's why the web is telling him it's a "pick some random locations near 0,0,0 till you find sand" approach, but his observation is that it's not.
So he thinks it's probably connected to the seed and therefor not random at all.

Somehow some of you only read every second word and post to form "Hey guys, wtf, this seed generates the same terrain every time, how does it do that?"
The post you quoted was him showing the spawn isn't random, not him trying to show the world generation with the same seed isn't random and trying to figure out why...

ZombieApostate posted:

It's probably just doing something along the lines of x = randomNumber(), y = randomNumber(), z = randomNumber(), in which case, all you need to know is how random numbers are generated. It might be incrementing the coords by the random numbers or something so you don't repeat or run through all the spaces in whatever limit you supply your random number generator, but that isn't really much of an algorithm, which is, I think, why everybody is giving similar answers about how random numbers are generated.

westborn posted:

He clearly does know how the seed for the terrain generation works. He was asking how the spawnpoint is determined afterwards, as Minecraft has/had the tendency to not always spawn you at the same point on the same seed.

quote:

If it's random, then it wouldn't be the same every time the same seed is used.

Red Mike posted:

No, he clearly doesn't. Here:


It's pseudo-random, and it uses the same seed, so it always spawns you at the same point on the same seed.

It just uses the generator as it does when it creates the terrain. This uses x numbers from the pseudo-random series. The next 3, x+1, x+2, and x+3 are used to generate the first location it tries to put the player on. These are always the same if you use the same seed, because of how pseudo-random generators work. He clearly does not understand this, or he wouldn't be asking why they're the same every time.

And yes, you misread and thought he was arguing that it doesn't spawn at the same point for the same seed, next time read a little further.

To answer you, it uses the first 3 numbers it gets after generating the world, then, if they aren't valid, increments each one by 1 until it gets a position that works. Considering the same seed will give you the same sequence of 3 numbers after world generation every time, obviously you'll get the same position for the same seed.

quote:

Yeah I know. What I mean is, Minecraft is using that seed in some equation that sets the spawn point. I'm trying to see if anyone knows what that equation is.

HaB posted:

I spent a few hours last night wading through the Minecraft sources, but following the chain backwards from where the player is actually spawned only leads me to one spot where it's grabbing 3 int values from an NbtTree (which seems to work like a hashtable but can return multiple types instead of just one). I assume the tree is populated using the map seed but hell if I can figure out where that's happening. Specifically:

from WorldInfo.java:

code:

spawnX = nbttagcompound.getInteger("SpawnX");
spawnY = nbttagcompound.getInteger("SpawnY");
spawnZ = nbttagcompound.getInteger("SpawnZ");

If I can just find where nbttree["SpawnX"] is actually getting populated, I'm there.

Pfhreak posted:

I think I see what's going on here. Most of us are abstracting your question of "How, exactly, does Minecraft generate a starting location?" into, "How do games typically generate a deterministic random set of variables?" For most of us, and for most of the questions in this thread, working at the abstraction level is pretty common for helping someone understand whatever problem they are working on.

It sounds to me like you have a project in mind ("I would like to be able to predict a start location for a given seed so I can use that value in my mod/hack/web thing/whatever.") But you haven't really talked about what it is, so it sounds like what you are asking is for general details about random world generation, of which Minecraft is an example.

ShoulderDaemon posted:

World.java has getInitialSpawnLocation() which boils down to this:

code:

Create random number generator seeded using world seed.
Find all biomes within 256 cells of (0,0) which are one of the 5 valid spawn biomes.
Choose one such biome randomly with equal weight.
Let (x,y) = the center of that biome.
Repeat:
  Find the uppermost block at (x,y).
  If that block is grass, you're done.
  x += rand(64) - rand(64)
  y += rand(64) - rand(64)

The "find all biomes" step is in still-obfuscated portions of minecraft's codebase, so my 5-minute-understanding of it may be mistaken.

Edit: For me, at least, a big part of the confusion with this whole thing is that this is an algorithm I would not be shocked to find described as "picks a location within a few hundred blocks of (0, 0) and tries to spawn, if it fails, it increments until it finds a valid location" so it's been weird that HaB seemed to want something more.

HaB posted:

Does anyone know the method by which Minecraft generates the initial player spawn based on the seed? All I can find from googling is a general "picks a location within a few hundred blocks of (0, 0) and tries to spawn, if it fails, it increments until it finds a valid location"

And that's all well and good except it's not random. If I start a world with a particular seed, open it up, check my spawn coords, then delete the world and re-create using the same seed, I get the same spawn point.

Red Mike posted:

Red Mike posted:

e: Christ almighty, I'm being pedantic and unhelpful. I'll stop this, my apologies.

HaB posted:

Does anyone know the method by which Minecraft generates the initial player spawn based on the seed? All I can find from googling is a general "picks a location within a few hundred blocks of (0, 0) and tries to spawn, if it fails, it increments until it finds a valid location"

And that's all well and good except it's not random. If I start a world with a particular seed, open it up, check my spawn coords, then delete the world and re-create using the same seed, I get the same spawn point.

So...does anyone know what method it's using to choose? Thanks in advance.

MrZig posted:

Thanks! I actually managed to get a PixelPerfectBitMask setup working properly, or at least good enough for now. I can start with a high res image, say 512x512, and have OpenGL refer to that for drawing, then for the bitmask I just used Android's createScaledBitmap to the object's actual size and presto, it works perfectly.

Edit: Ok apparently it still doesn't work properly. Goddamn this is hard. I don't know how to create a scaled bitmap. I tried the above method by basing it off of Android's createScaledBitmap but that doesn't seem to work either. Only works when I set BOTH objects colliding to the same exact size..

brian posted:

I guess make sure there aren't any offsets you're not aware of are at work and step through with a debugger or debug text write what the mask looks like internally and make sure it lines up with what you think it's meant to look like. I mean other than that it's just a case of getting the logic for the test right.