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tapped

Marching Cube Holes

6 posts in this topic

I have problem generating terrain in marching cubes. My marching cube implementation is in OpenCL. I have 16 * 16 * 16 voxels per block. It works fine when generating a sphere, the only problem is that you can see some small holes between some parts of the sphere. My theory is floating precision, but i dont know.

[url="http://imageshack.us/photo/my-images/833/failsphere.png/"]http://imageshack.us/photo/my-images/833/failsphere.png/[/url]

Another problem occur when i tries to generate terrain, with noise:

[url="http://imageshack.us/a/img689/1146/failterrain.png"]http://imageshack.us...failterrain.png[/url]

As you can see, it does not look well. This was rendered with isolevel 0.9f.

I create the terrain like:
[source lang="cpp"]sampler_t randomVolumeSampler = CLK_NORMALIZED_COORDS_TRUE | CLK_ADDRESS_REPEAT | CLK_FILTER_LINEAR;

density.x = wPos.y;
density.x += read_imagef(randomVolume, randomVolumeSampler, realGridPos).x * 0.25f;[/source]

So i was wondering, if i have implemented marching cube wrong, or if it behaves right, Edited by Tapped
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it depends on how you build your sphere.. with voxels the best test would be a n^3 for loop over the diameter, ie. dx is iterated (x-radius+1 to x+radius-1) etc.
that way you can be sure the sphere is complete
the terrain is unmistakably as the poster above me said, the noise doesn't use world-space coordinates.. or it's just an array you draw 4 times [img]http://public.gamedev.net//public/style_emoticons/default/tongue.png[/img] which is even more wrong Edited by Kaptein
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Thanks, i generate the noise with glm::perlin. First I create a random 3D vector, which is then being multiplied with the position in the random volume, then i use that as the seed for perlin.

The thing is that my blocks are 2.0 * 2.0 * 2.0 in opengl size. And 32 * 32 * 32 voxels per block, therefore 16 * 16 * 16 voxels per cubic meter(opengl). What you see on the picture is one block, so 4 cracks appear per block. So yeah, i believe it is some problem with the tiling of the random volume. However, how can i create a tileable noise volume. I have tried different techniques which did not fix the cracks, like using the same noise on all edges...

[CODE]
#define RANDOM_VOLUME_EXTENT 16

glm::vec3 randVec(glm::signedRand1<float>(), glm::signedRand1<float>(), glm::signedRand1<float>());
for(int i = 0;i < RANDOM_VOLUME_EXTENT;++i)
{
for(int j = 0;j < RANDOM_VOLUME_EXTENT;++j)
{
for(int k = 0;k < RANDOM_VOLUME_EXTENT;++k)
{
glm::vec3 p(i * randVec.x, j * randVec.y, k * randVec.z);
randBuffer[(i*RANDOM_VOLUME_EXTENT*RANDOM_VOLUME_EXTENT)+(j*RANDOM_VOLUME_EXTENT) + k] = glm::perlin(p);
}
}
[/CODE] Edited by Tapped
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Never mind, found enough information on how to create tileable perlin noise. Edited by Tapped
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Nice that you've fixed it (can you give some information or perhaps links for people of the future - hello guys!). I don't know but I'm pretty sure you only need a single seed for perlin noise, and that you then use the world position in the density function to sample the perlin noise directly (with a single seed, it can be sampled from -infinity to +infinity and will never have discontinuities, so you won't have that crack problem).
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Now i have implemented the information i got from: [url="http://gamedev.stackexchange.com/questions/23625/how-do-you-generate-tileable-perlin-noise"]http://gamedev.stack...le-perlin-noise[/url]
Even if i did that, i still had cracks, but then after a lot of testing of different sample types, i finally got it work. It worked when i used this sampler:
[CODE]
__constant sampler_t randomVolumeSampler = CLK_NORMALIZED_COORDS_TRUE | CLK_ADDRESS_MIRRORED_REPEAT | CLK_FILTER_LINEAR;


float4 realGridPos;
realGridPos.x = gridPos.x * voxelSize;
realGridPos.y = gridPos.y * voxelSize;
realGridPos.z = gridPos.z * voxelSize;

density.x += read_imagef(randomVolume, randomVolumeSampler, realGridPos).x * 0.8f;
[/CODE]

realGridPos is the same as the local position in terms of a block, which in this case range from [0.0, 2.0] for each block.
Here is the result:

[url="http://imageshack.us/a/img823/9383/itworks.png"]http://imageshack.us...383/itworks.png[/url]
Thanks for the help! [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img] Edited by Tapped
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