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tiling terrain seam


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#1 timothyjlaird   Members   -  Reputation: 404

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Posted 24 June 2012 - 10:44 AM

I'm trying to tile some terrain that I generated using height mapping. Basically I make a plane on the x/z axis and then change the 'y' values based on a height map. In order to make the terrain tile I averaged the 'y' values on sides of each block of terrain (there are 4). Problem is that I end up with a seam that actually lines up well but the lighting is all screwed up along the seam as you can see here...

Posted Image

I'm fairly confident this is because I am not calculating the normals quite right along the seam. This is the code I am using the calculate the normals:

//calc normals for smooth shading
			for (int counter = 0; counter < indexData.Length; counter += 3)
			{
				Vector3 v1 = vertexData[indexData[counter + 0]].Position;
				Vector3 v2 = vertexData[indexData[counter + 1]].Position;
				Vector3 v3 = vertexData[indexData[counter + 2]].Position;
				Vector3 vu = v3 - v1;
				Vector3 vt = v2 - v1;
				Vector3 normal = Vector3.Cross(vu, vt);
				normal.Normalize();
				vertexData[indexData[counter]].Normal += normal;
				vertexData[indexData[counter + 1]].Normal += normal;
				vertexData[indexData[counter + 2]].Normal += normal;
			}
			for (int counter = 0; counter < vertexData.Length; counter++)
			{
				vertexData[counter].Normal.Normalize();
			}

Any ideas on how to resolve this?

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#2 gnomgrol   Members   -  Reputation: 584

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Posted 25 June 2012 - 07:08 AM

How are the tiles buildet up? Each has its own Vertexbuffer?
The code for your normals seems correct, may you are calling it before you change the y-values of the vertices?
That caused the problem in my case, may its the same for you.

What does the code to average the y-values look like? Can you post it please?
Oh, another question I have, how do you make the textures fit together that perfectly in slope-based texturing?

Edited by gnomgrol, 25 June 2012 - 08:28 AM.


#3 timothyjlaird   Members   -  Reputation: 404

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Posted 25 June 2012 - 06:44 PM

How are the tiles buildet up? Each has its own Vertexbuffer?
The code for your normals seems correct, may you are calling it before you change the y-values of the vertices?
That caused the problem in my case, may its the same for you.

What does the code to average the y-values look like? Can you post it please?
Oh, another question I have, how do you make the textures fit together that perfectly in slope-based texturing?


The vertex and index buffers are the same for all 4 blocks of terrain. I simply change effect.World (translation matrix) each time, then draw.

Nope. The last thing I do is calculate the normals.

Here is the code I used for averaging the y-values along the edges:

private float[,] getMirroredVertexDataTwoDim(float[,] yvalues, int size)
	    {
		    float leftsidey;
		    float rightsidey;
		    float avgleftright;
		    float topsidey;
		    float bottomsidey;
		    float avgtopbottom;
		    for (int zcounter = 0; zcounter < size; zcounter++)
		    {
			    leftsidey = yvalues[0, zcounter];
			    rightsidey = yvalues[size - 1, zcounter];
			    avgleftright = (leftsidey + rightsidey) / 2.0f;
			    yvalues[0, zcounter] = avgleftright;
			    yvalues[size - 1, zcounter] = avgleftright;
		    }
		    for (int xcounter = 0; xcounter < size; xcounter++)
		    {
			    topsidey = yvalues[xcounter, 0];
			    bottomsidey = yvalues[xcounter, size - 1];
			    avgtopbottom = (topsidey + bottomsidey) / 2.0f;
			    yvalues[xcounter, 0] = avgtopbottom;
			    yvalues[xcounter, size - 1] = avgtopbottom;
		    }
		    return yvalues;
	    }

I'm not using slope-based texturing...just one big texture for each tile (2048x2048). A bit crude but effective. I used L3DT to make it for me.

#4 gnomgrol   Members   -  Reputation: 584

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Posted 26 June 2012 - 12:17 AM

Im sorry, I cant really figure out whats the cause of your problem.
Here is the code I use to calculate normals (DirectX):

Cant post in sourcetags, buggy somehow:

// GET ALL DA NORMALZ!!!
std::vector<D3DXVECTOR3>* normal_buffer = new std::vector<D3DXVECTOR3>[chunkVnum];

for( int i = 0; i<chunkInum; i += 3 ){
// get the three vertices that make the faces
D3DXVECTOR3 p1 = vertices[indices[i+0]].pos;
D3DXVECTOR3 p2 = vertices[indices[i+1]].pos;
D3DXVECTOR3 p3 = vertices[indices[i+2]].pos;

D3DXVECTOR3 v1 = p2 - p1;
D3DXVECTOR3 v2 = p3 - p1;
D3DXVECTOR3 normal;
D3DXVec3Cross(&normal, &v1, &v2);

D3DXVec3Normalize(&normal, &normal);

// Store the face's normal for each of the vertices that make up the face.
normal_buffer[indices[i+0]].push_back( normal );
normal_buffer[indices[i+1]].push_back( normal );
normal_buffer[indices[i+2]].push_back( normal );
}


// Now loop through each vertex vector, and avarage out all the normals stored.
for( int i = 0; i < chunkVnum; ++i )
{
for( int j = 0; j < normal_buffer[i].size(); ++j ) {
vertices[i].normal += normal_buffer[i][j];
}

vertices[i].normal /= normal_buffer[i].size();
D3DXVec3Normalize(&vertices[i].normal, &vertices[i].normal);
}


May it can help you in some way ;/
How do you load the heightmap on the chunk if you calculate x and z with the effect?

Edited by gnomgrol, 26 June 2012 - 12:34 AM.


#5 szecs   Members   -  Reputation: 2143

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Posted 26 June 2012 - 01:35 AM

Without looking into the code in detail, I assume you only use one block's geometry to calculate the normals. But the normals are affected by the neighbor blocks' geometry too.

#6 mark ds   Members   -  Reputation: 1268

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Posted 26 June 2012 - 05:16 AM

You should really use 2049x2049 textures, with a one pixel overlap on adjacent edges. This would solve this and other problems.

#7 timothyjlaird   Members   -  Reputation: 404

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Posted 26 June 2012 - 11:24 AM

To be more clear...the heightmap texture is only 256x256. The diffuse texture is 2048x2048. I have attached my terrain code (not everything, just terrain)...maybe that will help.

Without looking into the code in detail, I assume you only use one block's geometry to calculate the normals. But the normals are affected by the neighbor blocks' geometry too.

That makes sense. I guess I could just stitch a seam of quads between blocks but then I would not be able to translate them later...in order to give the illusion of infinite terrain.

Attached File  terrain.zip   3.18KB   30 downloads

#8 szecs   Members   -  Reputation: 2143

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Posted 26 June 2012 - 12:00 PM

mark ds' suggestion is good, even if (s)he misunderstood you. I think the best thing is to use overlap on the block borders. Better than fetching data from another block (because there is a reason for using blocks instead of one block)




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