# Drawing a Grid(Terrainlike)

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Hi Finally the Inputsystem for my engine works so now i just want to render a simple grid with an indexed Trianglelist...I tried to keep everything as clear as possible so i first wrote a basemsh class which just contains an Index-,a Vertexbuffer and a DWORD for the FVF...every class that will be renders should be a child of this class so i thought i'll make a very basic terrain class which just creates a grid of variable size with a variable number of subdivions... but something is worng with it..it definitly has something to do with the creation of the Vertex and Indexbuffer because if i fill 'em manually it works fine... My terrain Class:
#include "stdafx.h"
#include ".\terrain.h"
#include "ngEngine.h"

Terrain::Terrain(void)
{
FVF=D3DFVF_XYZ|D3DFVF_DIFFUSE;
}

Terrain::~Terrain(void)
{
}

void Terrain::Create(ngEngine *engine,D3DXVECTOR3 StartPoint,float xSize,float zSize,int xRes,int zRes)
{
m_pEngine=engine;
float RowHeight=zSize/zRes;
float ColWidth=xSize/xRes;
CreateVertices(StartPoint,RowHeight,ColWidth,xRes,zRes);
CreateIndices(xRes,zRes);
ConstructBuffers();

}
void Terrain::CreateVertices(D3DXVECTOR3 StartPoint,float RowHeight,float ColWidth,int xCount,int zCount)
{
for(int j=0;j<=zCount;j++)   //<--for every Row do:
{
for(int i=0;i<=xCount;i++) //<--for every Vert do:
{
TerrainVert Vertex;
Vertex.x=StartPoint.x+i*ColWidth;
Vertex.y=StartPoint.y;            //<---Terrain Height
Vertex.z=StartPoint.z+j*RowHeight;
Vertex.color=0xff00ff00;
Verts.push_back(Vertex);

}
}

}

void Terrain::CreateIndices(int xRes, int yRes)
{
for(int j=0;j<=yRes-1;j++) //<--For Every Row do:
{
for(int i=0;i<=xRes-1;i++) //<--For Every QUAD(!) do:
{
int Row=j*xRes;
//First Triangle
Indices.push_back(xRes*j+i+Row);
Indices.push_back(i+Row);
Indices.push_back(i+Row+1);

//Indices.push_back(xRes*j+i+1+Row);
//Second Triangle
Indices.push_back(i+Row);
Indices.push_back(i+1+Row);
Indices.push_back(xRes*j+i+1+Row);
}

}

}

void Terrain::ConstructBuffers()
{

//Create VertexBuffer:

if( FAILED( m_pEngine->g_pD3DDevice->CreateVertexBuffer(Verts.size()*sizeof(std::vector<TerrainVert>::value_type),
0,
FVF,
D3DPOOL_DEFAULT,
&pVBuffer,   //<---inherited from BaseMesh
NULL ) ) )
{
MessageBox(0,"Fetter Error1!","Error",0);
PostQuitMessage(1);
}
VOID *pVData;
pVBuffer->Lock(0,sizeof(std::vector<TerrainVert>::value_type),(void**)&pVData,0);	//lock buffer
std::vector<TerrainVert>::pointer Vptr = &Verts[0];
memcpy(pVData,Vptr,Verts.size()*sizeof(std::vector<TerrainVert>::value_type));						//copy data to buffer
pVBuffer->Unlock();

//Create IndexBuffer:
if(FAILED(m_pEngine->g_pD3DDevice->CreateIndexBuffer(Indices.size()*sizeof(std::vector<short>::value_type),D3DUSAGE_WRITEONLY,D3DFMT_INDEX16,D3DPOOL_MANAGED,&pIBuffer,NULL)))
{
MessageBox(0,"Fetter Error2!","Error",0);
PostQuitMessage(1);
}

VOID *pIData;
pIBuffer->Lock(0,sizeof(std::vector<short>::value_type),(void**)&pIData,0);	//lock buffer
std::vector<short>::pointer Iptr = &Indices[0];
memcpy(pIData,Iptr,Indices.size()*sizeof(std::vector<short>::value_type));	//copy data to buffer
pIBuffer->Unlock();
}

void Terrain::render()
{
m_pEngine->g_pD3DDevice->SetFVF(FVF); //<---inherited from BaseMesh
m_pEngine->g_pD3DDevice->SetStreamSource(0,pVBuffer,0,sizeof(std::vector<TerrainVert>::value_type));
m_pEngine->g_pD3DDevice->SetIndices(pIBuffer);
m_pEngine->g_pD3DDevice->DrawIndexedPrimitive(D3DPT_TRIANGLELIST,0,0,Verts.size(),0,(xDivs-1)*(zDivs-1)*2);

}


regards, m4gnus

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It would help if you posted the actual problem, too. Does it render nothing? Does it crash? Do you get an error message?

Also, whatever the problem:
- use the DirectX Debug runtime
- turn the Debug Ouput Level up to full
- look at the debug spew

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it renders nothing...

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Have you set the projection and view matricies?

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Assuming the matrices are correct (considering your said it works if you fill the buffers manually): I don't see any set up of xDivs and zDivs in your code. Perhaps these are 0?

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Never mind that, you're creating degenerate triangles in your index buffer. Take a look at the contents of your index buffer.

You want something like:
for (int j = 0; j < yRes; ++j){	for (int i = 0; i < xRes; ++i)	{		int Row = j * xRes;		//First Triangle		Indices.push_back(Row + i);		Indices.push_back(Row + i + 1);		Indices.push_back(Row + i + xRes);		//Second Triangle		Indices.push_back(Row + i + 1);		Indices.push_back(Row + i + 1 + xRes);		Indices.push_back(Row + i + xRes);	}}

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ok thx i was also thinking it is a mistake like this but i calculated the indices of some traingle on paper and it seemed alright... i too tired to fix it now so i'll post tomorrow if it has helped..

regards,
m4gnus

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Ok it finally draws something but just 1 single trinagle... the rest of the terrain is missing...

regards,
m4gnus

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That brings me back to the former question: how are xDivs and zDivs set up?
Set through your program with the debugger and check the debug spew.

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what do you mean by set up? they are both set to 4 in my main cpp..
do you really think a debugger can help me here? i would use a debugger if i had a runtime error

regards,
m4gnus

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