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# quad doesn't connect to last one

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Hi all, I am rendering some quads for a terrain, problem is as soon as I render the second quad, it isn''t connected to the first one due to it being a different height, code is shown below (I am using just triangle list - gotta start somewhere) : for(int j=0; j<31; j++) // 1024 is height size { for (int i=0; i<31; i++) { quadVertices[index].x = (i)* ScaleX; quadVertices[index].z = j+1; quadVertices[index].y = GetHeight(i,j+1) / 4; // next side quadVertices[index+1].x = (i+1)* ScaleX; quadVertices[index+1].z = j; quadVertices[index+1].y = GetHeight(i,j) / 4; // last side of triangle quadVertices[index+2].x = (i)* ScaleX; quadVertices[index+2].z = j; quadVertices[index+2].y = GetHeight(i,j) / 4; // next triangle quadVertices[index+3].x = (i)* ScaleX; quadVertices[index+3].z = j+1; quadVertices[index+3].y = GetHeight(i,j + 1) / 4; quadVertices[index+4].x = (i + 1)*ScaleX; quadVertices[index+4].z = j+1; quadVertices[index+4].y = GetHeight(i,j + 1) / 4; quadVertices[index+5].x = (i+1)* ScaleX; quadVertices[index+5].z = j; quadVertices[index+5].y = GetHeight(i,j) / 4; index = index + 6; } How can I get the next quad to connect to previous one ? Kind regards, Steve

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Hi,

You should use your vertices only to represent your heights.. if so much edges are shared like in a terrain you should always use indices (which enables caching on your gfx card and saves heaps of memory). If you want to calculate your vertices for a batch of 32x32 (heightpoints), you get 32x32 vertices and 31x31 Quads (= 31*31*6 Indices). Now you have to create your Triangles by setting your Indices this way (prepare for awful ASCII-mania

1--2--3
| /| /|
|/ |/ |
4--5--6
| /| /|
|/ |/ |
7--8--9

That''s 4 quads = 8 triangles.. now create your triangles that way:

t1: 1-2-4
t2: 2-5-4
t3: 2-3-5

.. be careful that the winding is always clockwise or counter-clockwise. These values can be directly stored in your batch IndexBuffer and voila.. DrawIndexedPrimitive()

Hope that helps,
narbo

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Thanks guys,

My terrain is working with triangle lists at the moment, it is now working fine, I found some code on the web which was using same method as mine but there height worked! I''m still curious though as to how you do get the y value, I know it is from the height map, but in my code I am doing as follows:

quadVertices[index].x = (i)* ScaleX;
quadVertices[index].z = j;
quadVertices[index].y = GetHeight(i,j) / 15;

quadVertices[index+1].x = (i+1)* ScaleX;
quadVertices[index+1].z = j;
quadVertices[index+1].y = GetHeight(i+1,j) / 15;

quadVertices[index+2].x = (i+1)* ScaleX;
quadVertices[index+2].z = j+1;
quadVertices[index+2].y = GetHeight(i+1,j+1) / 15;
quadVertices[index+3].x = (i)* ScaleX;
quadVertices[index+3].z = j;
quadVertices[index+3].y = GetHeight(i,j) / 15;

quadVertices[index+4].x = (i + 1)*ScaleX;
quadVertices[index+4].z = j+1;
quadVertices[index+4].y = GetHeight(i+1,j+1) / 15;

quadVertices[index+5].x = (i)* ScaleX;
quadVertices[index+5].z = j+1;
quadVertices[index+5].y = GetHeight(i,j+1) / 15;

float GetHeight(int i, int j)
{
return pData[i*31+j];
}

If you look how I get the height for the y value, I''m still not sure how this works, how would I draw this down on paper?

Many thanks,
Steve

As I get older, my mind becomes more cluttered.

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You might want to look at implementing index buffers. It will greatly improve your FPS and I think it actually makes the code more readable:

// First add each vertex.
// Add vertex just adds the vertex to the vertex buffer, increments the vertex count, sets up texture coords, and returns the index.

nCenter = AddVertex ( NW_X + nRadius, NW_Y + nRadius, GetHeight ( NW_X + nRadius, NW_Y + nRadius ) );
nNE = AddVertex (NW_X + nQuadWidth, NW_Y,GetHeight ( NW_X + nQuadWidth, NW_Y ) );
nNW = AddVertex (NW_X, NW_Y, GetHeight ( NW_X, NW_Y ) );
nSW = AddVertex (NW_X, NW_Y + nQuadWidth , GetHeight ( NW_X, NW_Y + nQuadWidth ) );
nSE = AddVertex (NW_X + nQuadWidth, NW_Y + nQuadWidth ,GetHeight ( NW_X + nQuadWidth, NW_Y +nQuadWidth ) );

// First triangle
m_Indices[m_IndexCount++] = nNW;
m_Indices[m_IndexCount++] = nSW;
m_Indices[m_IndexCount++] = nNE;

//Second triangle
m_Indices[m_IndexCount++] = nNE;
m_Indices[m_IndexCount++] = nSW;
m_Indices[m_IndexCount++] = nSE;

My engine is still very much in development, but you're welcome to take a look at the full source:

CVS - http://cvs.bpopp.net/cgi-bin/cvsweb.cgi/terrain/
Journal - http://www.bpopp.net/articles/view.php?id=403

[edited by - bpopp on March 26, 2003 12:10:09 PM]

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