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I'm working on a terrain generator. Through multiple noise functions, I'm able to create many kinds of terrain I like, but I'm having a bit of difficulty joining them together in a seamless fashion.

My first thought was to use a single noise call (calling it the mask) and then I could simply say things like:

if (returnVal < .1) GenerateBiome1();
if (returnVal < .2) GenerateBiome2();
if (returnVal < .3) GenerateBiome3();

and so on...

The issue here is that the height of the terrain doesn't blend together when doing this. If biome 1 was more mountainous and biome 2 was flat land, it's a drastic switch from one to the other and it looks atrocious.

My next thought was to attempt blending by giving a 'strength' to each biome based on what my mask noise returns. In C# code, it looks something like this at the moment:

static public float GetHeight(float X, float Z)
    float fRollingHills_Location = .25f, fRollingHills_Impact = .5f, fRollingHills = 0;
    float fMountains_Location = .75f, fMountains_Impact = .5f, fMountains = 0;

    float fMask = Game1.GetNoise2(0, X, Z, .01f);
    float fRollingHills_Strength = (fRollingHills_Impact - Math.Abs(fMask - fRollingHills_Location)) / fRollingHills_Impact;
    float fMountains_Strength = (fMountains_Impact - Math.Abs(fMask - fMountains_Location)) / fMountains_Impact;

    if (fRollingHills_Strength > 0) fRollingHills = fRollingHills_Strength * (Game1.GetNoise2(0, X, Z, .02f) * 10f + 10f);
    if (fMountains_Strength > 0) fMountains = fMountains_Strength * (Game1.GetNoise2(0, X, Z, .05f) * 25f + 10f);

    return fRollingHills + fMountains;

The issue I have here is that even for only two biomes, it's pretty important for me to manually choose the "location" and "impact" values to ensure I'm getting some combination of strengths to total 100% by the time it returns a value (if not, I get things like giant cliffs making the borders from one biome to another ugly and obvious).

I don't know if I can give a good true question here other than, how should I actually be going about this? While I've managed a few good looking maps, I feel like I'm going about this in an overly complicated way that still doesn't give me all the customization I'm looking for.

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What I've done in the past is leave a gap between biomes that act as buffer zones. Certain aspects carry over from nearby zones (snow, trees, that sorta thing) and the gaps try to fall/rise from the edges to meet height variations. This creates a weathered look on mountain tops, and a rise up to the bottom of a cliff. Looks very natural. – DampeS8N May 17 '13 at 19:41
up vote 1 down vote accepted

3D Graphic with XNA Game Studio 4.0 has a chapter dedicated to this topic. It includes a complete process for generating the terrain and layering it with a variety of textures.

As luck would have it, that chapter is the sample provided by Packt on the book's page:

In this chapter, we will focus on building a full 3D environment. We will start by creating a class that builds a terrain from a 2D image called a heightmap . We will make a number of improvements to the basic version of this class, allowing multiple textures across its surface through multitexturing and extra detail at close distances to its surface through a "detail texture". We will look at a technique called region growing to add plants and trees to the terrain's surface, and fi nish by combining the terrain with our sky box, water, and billboarding effects to create a mountain scene..."

Sample chapter 7 pdf

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