Weird patterns in Dungeon Generation (Java)

[devout maple]

Hey everyone, I’m running into a strange issue with my dungeon generator.

I’m using a central java.util.Random object with a fixed seed, which I pass down to my logic classes (RoomLogic, PathLogic, etc.). Theoretically, it should be fine, but I keep getting repetitive, "unnatural" patterns in the layout that I can't explain.

The Setup: Standard Random object passed via a Config class.

The Issue: The distribution feels "off" almost like there's a bias in how rooms are placed.

My questions:

Is java.util.Random known for** poor distribution** in 2D/3D grid generation?

Should I switch to something like a Mersenne Twister or XorShift?

Or is this more likely a "Modulo Bias" / logic error in how I map coordinates?

Has anyone dealt with "non-random" looking randomness before? Any advice on how to debug this would be huge. Thanks!

    public boolean roomPlacement(ZoneConfig zoneConfig) {

        //---PLATZIERUNGS-VERSUCHE---//
        for (int i = 0; i < maxTries; i++) {
            
            //---ZONE ROTIEREN---//
            Zone rotatedZone = zoneConfig.getZone().get(Direction.getRandomDirection(random));

            ZoneSize size = rotatedZone.getZoneSize();

            //---GRID GRENZEN BERECHNEN---//
            int minX = 0 - size.getxMin();
            int maxX = g.xSize - 1 - size.getxMax();

            int minY = 0 - size.getyMin();
            int maxY = g.ySize - 1 - size.getyMax();

            int minZ = 0 - size.getzMin();
            int maxZ = g.zSize - 1 - size.getzMax();

            //---ZUFÄLLIGE POSITION---//

            int x = random.nextInt(maxX - minX + 1) + minX;
            int y = random.nextInt(maxY - minY + 1) + minY;
            int z = random.nextInt(maxZ - minZ + 1) + minZ;

            //---FÜR TOP ODER BOTTOM LAYER ROOMS---//
            if (zoneConfig.getLayer() == Layer.BOTTOM) {
                z = size.getzMin()*-1;

                for (int j = 0; j < size.getDiameterZ(); j++) {
                    if(g.getFillRatioOnZ(j) > targetFillRatio) {
                        return false;
                    }
                }
            }else if(zoneConfig.getLayer() == Layer.TOP) {
                z = g.zSize - size.getzMax() - 1;

                for (int j = g.zSize; j > size.getDiameterZ(); j--) {
                    if(g.getFillRatioOnZ(j-1) > targetFillRatio) {
                        return false;
                    }
                }
            }

            //---PLATZIERUNG PRÜFEN---//
            if (g.canPlace(rotatedZone, x, y, z)) {
                g.addRoom(rotatedZone, x, y, z);
                Log.info("Placed Room after [" + i + "] tries.");
                return true;
            }
        }

        //---KEINE PLATZIERUNG MÖGLICH---//
        Log.warning("Couldnt Place Room after [" + maxTries + "] tries.");
        return false;
    }

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[devout maple]

this happens in every generation at least once, can happen with any room, its very strange behaviour

it doenst matter how many different seeds or randoms i use, its always the same strange patterns

[dry holly]

Instead of random.nextInt(max - min + 1) + min you can just call random.nextInt(min, max + 1).

But I cannot see what should be off about those placements.

[native anchor]

One thing you could test is using SecureRandom which should have higher entropy

Also when you get into the conditional zoneConfig.getLayer() == Layer.BOTTOM, did you intentionally use *-1 (i.e. changing the sign) in z = size.getzMin()*-1?

[devout maple]

Yeah the *-1 is on purpose

[devout maple]

thanks yeah i will change that

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[devout maple]

i already tried that.
tried RandomGenerator too, same strange patterns.

but i decided to rewrite the entired generator, instead of bruteforce i wanted to backtrack the entired algorythm.

still need to find a way tho

[native anchor]

I am not entirely sure what the roomPlacement method is supposed to do