Hello every . I am new here .

I have a problem with the understanding of view matrix .

I draw a polyline with DrawPrimitive(D3DPT_LEINSTRIP , ...) in the x-y plane . And I put the eye in (0.0f,0.0f,-10.0f) . But I can not see the image .

But when I do not set the view matrix and projection matrix , the image will display . I do not know why .

This is my vertex buffer :

void Exercise::buildVB()
{
//get Direct3D Device
IDirect3DDevice9* _pDevice = m_pD3d->getDevice();

//craete the vertex buffer
HR(_pDevice->CreateVertexBuffer(6 * sizeof(VertexPos),D3DUSAGE_WRITEONLY,0,
D3DPOOL_MANAGED,&m_pVB,0));

//lock the vertex buffer
VertexPos * _pData = NULL ;
HR(m_pVB->Lock(0,0,(void**)&_pData,0));

//set the vertex
/*_pData[0] = VertexPos(0.0f, 0.0f, 0.0f);
_pData[1] = VertexPos(1.0f, 0.0f, -3.0f);
_pData[2] = VertexPos(3.0f, 0.0f, -2.0f);
_pData[3] = VertexPos(2.0f, 0.0f, -1.0f);
_pData[4] = VertexPos(2.5f, 0.0f, 1.0f);
_pData[5] = VertexPos(1.0f, 0.0f, 3.0f);*/
_pData[0] = VertexPos(0.0f, 0.0f, 0.0f);
_pData[1] = VertexPos(0.1f, -0.3f,0.0f );
_pData[2] = VertexPos(0.3f, -0.2f, 0.0f);
_pData[3] = VertexPos(0.2f, -0.1f,0.0f );
_pData[4] = VertexPos(0.25f, 0.1f,0.0f );
_pData[5] = VertexPos(0.1f, 0.3f,0.0f );


//unlock the vertex buffer
HR(m_pVB->Unlock());
}

This is the draw method which draw the image :

void Exercise::draw()
{
//get Direct3D Device
IDirect3DDevice9* _pDevice = m_pD3d->getDevice();

//set stream source
HR(_pDevice->SetStreamSource(0,m_pVB,0,sizeof(VertexPos)));

//set the index
//HR(_pDevice->SetIndices(m_pIB));

//set the vertex declaration
HR(_pDevice->SetVertexDeclaration(VertexPos::_vertexDecl));

//set the world matrix
D3DXMATRIX _worldM ;
HR(_pDevice->SetTransform(D3DTS_WORLD,D3DXMatrixIdentity(&_worldM)));

//set the view matrix
HR(_pDevice->SetTransform(D3DTS_VIEW,&m_ViewM));

//set the projection matrix
HR(_pDevice->SetTransform(D3DTS_PROJECTION,&m_ProjM));

//set the render state
HR(_pDevice->SetRenderState(D3DRS_FILLMODE,D3DFILL_WIREFRAME));

//draw the primitive
HR(_pDevice->DrawPrimitive(D3DPT_LINESTRIP,0,6));

}

Here is my code about the view matrix and projection matrix:

void Exercise::buildViewM()
{
D3DXVECTOR3 _pos(0.0f,0.0f,-10);
D3DXVECTOR3 _target(0.0f,0.0f,0.0f);
D3DXVECTOR3 _up(0.0f,1.0f,0.0f);
D3DXMatrixLookAtLH(&m_ViewM,&_pos,&_target,&_up);
}

void Exercise::buildProjM()
{
float _width = m_pD3d->getD3dParam().BackBufferWidth;
float _height = m_pD3d->getD3dParam().BackBufferHeight;
D3DXMatrixPerspectiveFovLH(&m_ProjM,D3DX_PI,_width/_height,1.0f,1000.0f);
}

Is there any problem with my code ???

I appriciate your help .

In such cases always start out weeding options.

Turn off lightning. Turn off cull mode. Turn off zbuffer. Set Texture to NULL (yes, wireframes can be textured)

Make the camera controllable and look around :)

Thank you for your help . I had alread solved this problem .