Question

I am new to DirectX and I am trying to draw two rectangles in one scene using D3DPT_TRIANGLESTRIP. One Rectangle is no problem but two Rectangles is a whole different ball game. Yes i could draw them using four triangles drawn with the D3DPT_TRIANGLELIST primitive type. My curiosity is on the technic involved using D3DPT_TRIANGLESTRIP.
Parts of the code i am using for one Rectangle using D3DPT_TRIANGLESTRIP is as follows:

CUSTOMVERTEX recVertex[] = {
    {  10.0f,  10.0f, 0.10f, 1.0f, 0xffffffff, }, // x, y, z, rhw, color
    { 220.0f,  10.0f, 0.10f, 1.0f, 0xffffffff, },   
    {  10.0f, 440.0f, 0.10f, 1.0f, 0xffffffff, },   
    { 220.0f, 440.0f, 0.10f, 1.0f, 0xffffffff, },
}; 

if( FAILED( g_pd3dDevice->CreateVertexBuffer( 4 * sizeof( CUSTOMVERTEX ),
               0, D3DFVF_CUSTOMVERTEX, D3DPOOL_DEFAULT, &g_pVB, NULL ) ) )
{
    return E_FAIL;
}

More vital code…

VOID* precVertex;    
if( FAILED( g_pVB->Lock( 0, sizeof( recVertex ), ( void** )&pGameField, 0 ) ) ) 
{
return E_FAIL; 
}
 memcpy( precVertex, recVertex, sizeof( recVertex ) );

then Render like so…

g_pd3dDevice->SetStreamSource( 0, g_pVB, 0, sizeof( CUSTOMVERTEX ) );
g_pd3dDevice->SetFVF( D3DFVF_CUSTOMVERTEX );
g_pd3dDevice->DrawPrimitive( D3DPT_TRIANGLESTRIP, 0, 2 );

Based on this model I could easily duplicate the code change the x and y values on the Custom Vertex and create another vertex buffer and it would work.

Personally i feel this is not the best way to go especially considering a situation when i have to draw say 100 rectangles or something like that. The thing is, I don’t have other ideas. So my question is, what is the most efficient way to draw two Rectangles with D3DPT_TRIANGLESTRIP? Also is there a possible way of duplicating and transforming the current rectangle?

Answer 1

Add the four vertices for the second rectangle to the vertex buffer, then call DrawPrimitive twice.

g_pd3dDevice->SetStreamSource( 0, g_pVB, 0, sizeof( CUSTOMVERTEX ) );
g_pd3dDevice->SetFVF( D3DFVF_CUSTOMVERTEX );
g_pd3dDevice->DrawPrimitive( D3DPT_TRIANGLESTRIP, 0, 2 );
g_pd3dDevice->DrawPrimitive( D3DPT_TRIANGLESTRIP, 4, 2 );