A really weird directx(direct3d) problem

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the purpose is to create a mesh of teapot,get the vertices & index from it,and draw from the vertices and index

C++

ID3DXMesh *Teapot;

D3DXCreateTeapot(dev,&Teapot,NULL);

Teapot->DrawSubset(0);

dev->Clear(0, 0, D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER, 0xffffffff, 1.0f, 0);

IDirect3DVertexBuffer9 *VertextBuffer;
IDirect3DIndexBuffer9 *IndexBuffer;

DWORD NumFaces=Teapot->GetNumFaces();
DWORD NumVertices=Teapot->GetNumVertices();
DWORD BytesPerVertex=Teapot->GetNumBytesPerVertex();

if(Teapot->GetVertexBuffer(&VertextBuffer)!=D3D_OK)MessageBox(NULL,TEXT("GetVertexBuffer() Failed!!"),TEXT(""),MB_OK);
if(Teapot->GetIndexBuffer(&IndexBuffer)!=D3D_OK)MessageBox(NULL,TEXT("GetIndexBuffer() Failed!!"),TEXT(""),MB_OK);
if(dev->SetStreamSource(0,VertextBuffer,0,BytesPerVertex)!=D3D_OK)MessageBox(NULL,TEXT("SetStreamSource() Failed!!"),TEXT(""),MB_OK);

dev->BeginScene();
if(dev->DrawIndexedPrimitive(D3DPT_TRIANGLELIST,0,0,NumVertices,0,NumFaces)!=D3D_OK)MessageBox(NULL,TEXT("DrawIndexedPrimitive() Failed!!"),TEXT(""),MB_OK);

dev->EndScene();
dev->Present(0,0,0,0);

everything's ok!Wonderful!!!
But
if I just delete the code "Teapot->DrawSubset(0);" at line 5th,the messagebox will tell me

DrawIndexedPrimitive() Failed!!

Just want to know WHY
WEll,English is my 2nd language so I'm not really good at it,but you know what I mean
Thank you

Posted 7-Feb-13 21:43pm

Aweiwei_

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Fredrik Bornander 8-Feb-13 4:56am

What error is returned by SetStreamSource?

Aweiwei_ 11-Feb-13 0:09am

It works well.No error was reported.

Fredrik Bornander 11-Feb-13 2:28am

Sorry, I meant what error is reported by dev->DrawIndexedPrimitive(D3DPT_TRIANGLELIST,0,0,NumVertices,0,NumFaces)?

Aweiwei_ 12-Feb-13 8:13am

int err=dev->DrawIndexedPrimitive(D3DPT_TRIANGLELIST,0,0,NumVertices,0,NumFaces);

err come out to be -2005530516 (0x8876086c)

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Matthew Faithfull · Answer 1 · 2013-02-07T23:24:00

Solution 1

My guess would be that's because there's nothing in the triange list without the call to DrawSubset(0)
Look at the documentation for DrawSubset to see why you would need to call it.
To me it implies in a Microsoft, 'we said it even though we didn't really say it' way that DrawSubset turns a mesh or part of a mesh into a triangle list to be rendered by DrawIndexedPrimitive.

Posted 7-Feb-13 23:24pm

Matthew Faithfull

Comments

Aweiwei_ 11-Feb-13 0:07am

from msdn:

Remarks

The subset that is specified by AttribId will be rendered by the IDirect3DDevice9::DrawIndexedPrimitive method, using the D3DPT_TRIANGLELIST primitive type, so an index buffer must be properly initialized.

it seems that the DrawSubset call DrawIndexedPrimitive internal