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docs/Generator: Added the easy Finishers.

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madmaxoft 2014-06-07 13:59:10 +02:00
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docs/Generator.html
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@ -386,14 +386,129 @@ and use the layout corresponding to the threshold:</p>
<img src="img/perlincompositor2.jpg" />
<img src="img/perlincompositor3.jpg" />
<h3>Nether composition</h3>
<p>So far we've been discussing only the Overworld generator. But MineCraft contains more than that. The
Nether has a completely different look and feel, and quite different processes are required to generate that.
Recall that MineCraft's Nether is 128 blocks high, with bedrock both at the top and the bottom. Between these
two, the terrain looks more like a cavern than a surface. Not surprisingly, the Nether doesn't need a
complicated height generator, it can use the flat height. However, the terrain composition must take an
altogether different approach.</p>
<p>The very first idea is to use the Perlin noise, but generate it in 3D, rather than 2D. Then, for each
block, evaluate the noise value, if below 0, make it air, if not, make it netherrack.
<p>To make it so that the bedrock at the top and at the bottom is never revealed, we can add a value
increasing the more the Y coord gets towards the bottom or the top. This way the thresholding then guarantees
that there will be no air anywhere near the bedrock.</p>
<p>(TODO)</p>
<hr />
<a name="finishgen"><h2>Finishers</h2></a>
<p>(TODO)</p>
<p>Finishers are a vast category of various additions to the terrain generator. They range from very easy
ones, such as generating snow on top of the terrain in cold biomes, through medium ones, such as growing
patches of flowers, complicated ones, such as placing trees and generating caves, all the way to very
complicated ones such as villages and nether fortresses. There is no formal distinction between all these
"categories", the only thing they have in common is that they take a chunk of blocks and modify it in some
way.</p>
<h3>Snow</h3>
<p>Snow is probably the easiest of the finishers. It generates a block of snow on top of each block that is
on top of the terrain and is not marked as non-snowable. It checks the chunk's heightmap to determine the top
block, then checks whether the block supports snow on its top. Rails, levers and grass don't support snow,
for example.</p>
<h3>Ice</h3>
<p>Another example of an easy finisher. This scans through the world and turn each water block on the surface
into an ice block if the biome is cold. This means that any water block that is under any kind of other
block, such as under a tree's leaves, will still stay water. Thus an additional improvement could be made by
scanning down from the surface block through blocks that we deem as non-surface, such as leaves, torches,
ladders, fences etc. Note that MCServer currently implements only the easy solution.</p>
<h3>Bottom lava</h3>
<p>Most worlds in MineCraft have lava lakes at their bottom. Generating these is pretty straightforward: Use
the user-configured depth and replace all the air blocks below this depth with lava blocks. Note however,
that this makes this generator dependent on the order in which the finishers are applied. If the mineshafts
generate before bottom lava, the mineshafts that are below the lava level will get filled with lava. On the
other hand, if bottom lava is generated before the mineshafts, it is possible for a mineshaft to "drill
through" a lake of lava. MCServer doesn't try to solve this and instead lets the admin choose whichever they
prefer.</p>
<h3>Specific foliage</h3>
<p>There are generators for specific kinds of foliage. The dead bushes in the desert biome and lilypads in
the swamp biome both share the same generating pattern. They are both specific to a single biome and they
both require a specific block underneath them in order to generate. Their implementation is simple: pick
several random columns in the chunk. If the column is of the correct biome and has the correct top block,
add the foliage block on top.</p>
<p>In order to generate the same set of coordinates when the chunk is re-generated, we use the Perlin noise's
basis functions (the ones providing the random values for Perlin cell vertices). These basically work as a
hash function for the coorinates - the same input coordinates generate the same output value. We use the
chunk's coordinates as two of the coords, and the iteration number as the third coordinate, to generate a
random number. We then check the biome and the top block at those coordinates, if they allow, we generate the
foliage block on top.</p>
<p>Another example of specific foliage is the tall grass in the plains biome. There are quite a lot of these
tall grass blocks, it would be inefficient to generate them using the random-coords approach described above.
Instead, we will use a 2D Perlin noise again, with a threshold defining where to put the grass and where
not.</p>
<h3>Small foliage</h3>
<p>For the flowers, grass, mushrooms in caves etc. we want to use a slightly different algorithm. These
foliage blocks are customarily generated in small "clumps" - there are several blocks of the same type near
together. To generate these, we first select random coords, using the coord hash functions, for a center of a
clump. Then we select the type of block to generate. Finally, we loop over adding a random (coord hash)
number to the clump center coords to get the block where to generate the foliage block:</p>
<img src="img/smallfoliageclumps.jpg" />
<p>In order to make the clump more "round" and "centered", we want the offsets to be closer to the clump
center more often. This is done using a thing called Gaussian function distribution. Instead of having each
random number generate with the same probability, we want higher probability for the numbers around zero,
like this:</p>
<img src="img/gaussprobability.jpg" />
<p>Instead of doing complicated calculations to match this shape exactly, we will use a much easier shape.
By adding together two random numbers in the same range, we get the probability distribution that has a
"roof" shape, enough for our needs:</p>
<img src="img/roofprobability.jpg" />
<p>(For the curious, there is a proof that adding together infinitely many uniform-distributed random number
produces random numbers with the Gaussian distribution.)</p>
<p>This scheme can be used to produce clumps of flowers, when we select the 2D coords of the clump center on
the top surface of the terrain. We simply generate the 2D coords of the foliage blocks and use the terrain
height to find the third coord. If we want to generate clumps of mushrooms in the caves, however, we need to
generate the clump center coords in 3D and either use 3 offsets for the mushrooms, or use 2 offsets plus
searching for the closest opening Y-wise in the terrain.</p>
<h3>Springs</h3>
<p>Water and lava springs are essential for making the underground quite a lot more interesting. They are
rather easy to generate, but a bit more difficult to get right. Generating simply means that a few random
locations (obtained by our familiar coord hashing) are checked and if the block type in there is stone. Then
we see all the horizontal neighbors of the block, plus the block underneath. If all of them except one are
stone, and the one left is air, our block is suitable for turning into a spring. If there were more air
neighbors, the spring would look somewhat unnatural; if there were no air neighbors, the spring won't flow
anywhere, so it would be rather useless.</p>
<p>The difficult part about springs is the amount of them to generate. There should be a few springs on the
surface, perhaps a bit more in the mountaineous biomes. There should be quite a few more springs underground,
but there should definitely be more water springs than lava springs in the upper levels of the terrain, while
there should be more lava springs and almost no water springs near the bottom. To accomodate this, the
MCServer team has made a tool that scanned through MineCraft's terrain and counted the amount of both types
of springs in relation to their height. Two curves have been found for the distribution of each type of the
spring:</p>
<img src="http://mc-server.xoft.cz/img/vanilla_springs_huge.png" />
<p>MCServer uses an approximation of the above curves to choose the height at which to generate the
spring.</p>
<!--
<h3>Caves</h3>
<p>Caves are definitely one of the main things people notice about MineCraft terrain. There are quite a lot
of different algorithms available to generate terrain with caves.
-->
<hr />

12
src/Generating/CompoGen.cpp
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@ -561,10 +561,16 @@ void cCompoGenNether::ComposeTerrain(cChunkDesc & a_ChunkDesc)
// Interpolate the lowest floor:
for (int z = 0; z <= 16 / INTERPOL_Z; z++) for (int x = 0; x <= 16 / INTERPOL_X; x++)
{
//*
FloorLo[INTERPOL_X * x + 17 * INTERPOL_Z * z] =
m_Noise1.IntNoise3DInt(BaseX + INTERPOL_X * x, 0, BaseZ + INTERPOL_Z * z) *
m_Noise2.IntNoise3DInt(BaseX + INTERPOL_X * x, 0, BaseZ + INTERPOL_Z * z) /
256;
//*/
/*
FloorLo[INTERPOL_X * x + 17 * INTERPOL_Z * z] =
m_Noise1.IntNoise3DInt(BaseX + INTERPOL_X * x, 0, BaseZ + INTERPOL_Z * z) / 256;
//*/
} // for x, z - FloorLo[]
LinearUpscale2DArrayInPlace<17, 17, INTERPOL_X, INTERPOL_Z>(FloorLo);
@ -574,10 +580,16 @@ void cCompoGenNether::ComposeTerrain(cChunkDesc & a_ChunkDesc)
// First update the high floor:
for (int z = 0; z <= 16 / INTERPOL_Z; z++) for (int x = 0; x <= 16 / INTERPOL_X; x++)
{
//*
FloorHi[INTERPOL_X * x + 17 * INTERPOL_Z * z] =
m_Noise1.IntNoise3DInt(BaseX + INTERPOL_X * x, Segment + SEGMENT_HEIGHT, BaseZ + INTERPOL_Z * z) *
m_Noise2.IntNoise3DInt(BaseX + INTERPOL_Z * x, Segment + SEGMENT_HEIGHT, BaseZ + INTERPOL_Z * z) /
256;
//*/
/*
FloorHi[INTERPOL_X * x + 17 * INTERPOL_Z * z] =
m_Noise1.IntNoise3DInt(BaseX + INTERPOL_X * x, Segment + SEGMENT_HEIGHT, BaseZ + INTERPOL_Z * z) / 256;
//*/
} // for x, z - FloorLo[]
LinearUpscale2DArrayInPlace<17, 17, INTERPOL_X, INTERPOL_Z>(FloorHi);