DirectX Array of vertices draws, Vector of vertices does not draw

Question

This code works fine:

    Vertex cubeVertices[] = 
    {
        {XMFLOAT3(-0.5f, -0.5f, -0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
        {XMFLOAT3(-0.5f, -0.5f,  0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
        {XMFLOAT3(-0.5f,  0.5f, -0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
        {XMFLOAT3(-0.5f,  0.5f,  0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
        {XMFLOAT3( 0.5f, -0.5f, -0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
        {XMFLOAT3( 0.5f, -0.5f,  0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
        {XMFLOAT3( 0.5f,  0.5f, -0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
        {XMFLOAT3( 0.5f,  0.5f,  0.5f), XMFLOAT3(0.0f, 0.133f, 0.333f)},
    };

    D3D11_SUBRESOURCE_DATA vertexBufferData = {0};
    vertexBufferData.pSysMem = cubeVertices;
    vertexBufferData.SysMemPitch = 0;
    vertexBufferData.SysMemSlicePitch = 0;

            //THE PROBLEM IS HERE
            //if I use sizeof(m_Vertices) it no longer works.
            //I still don't understand though because m_Vertices should still be in scope
    CD3D11_BUFFER_DESC vertexBufferDesc(sizeof(cubeVertices), D3D11_BIND_VERTEX_BUFFER);
    DX::ThrowIfFailed(
        m_d3dDevice->CreateBuffer(
            &vertexBufferDesc,
            &vertexBufferData,
            &m_vertexBuffer));

It draws a lovely cube on my screen.

This code does not work:

    GeometryGenerator generator;
    GeometryGenerator::MeshData cubeData;
    generator.CreateCube(cubeData);

            //I thought it might be a scope problem
            //m_Vertices is a std::Vector<Vertex>
    m_Vertices.resize(cubeData.Vertices.size());

    for(size_t i = 0; i < cubeData.Vertices.size(); ++i)
    {
        m_Vertices[i].pos = cubeData.Vertices[i].Position;          
        m_Vertices[i].color = XMFLOAT3(0.0f, 0.133f, 0.333f);
    }

    D3D11_SUBRESOURCE_DATA vertexBufferData = {0};
    vertexBufferData.pSysMem = &m_Vertices[0];
    vertexBufferData.SysMemPitch = 0;
    vertexBufferData.SysMemSlicePitch = 0;

            //THE PROBLEM IS HERE
            //if I use sizeof(m_Vertices) it no longer works.
            //I still don't understand though because m_Vertices should still be in scope
    CD3D11_BUFFER_DESC vertexBufferDesc(sizeof(m_Vertices), D3D11_BIND_VERTEX_BUFFER);
    DX::ThrowIfFailed(
        m_d3dDevice->CreateBuffer(
            &vertexBufferDesc,
            &vertexBufferData,
            &m_vertexBuffer));

The screen clears to my clear color but no shapes draw on the screen.

I thought &m_Vertices[0] is equivalent to an array? I've checked the values in debug and both the array and my CreateCube function produce the same data.

must be something else then, do you properly initialize all world and projection matrices ? — Radu Chivu, Oct 21 '13 at 21:21
Yes, if I take the lower black and change it to the upper block and make no other changes it works. — Eric, Oct 21 '13 at 21:30
might be because the compiler pads the structure you're using to represent a vertex, can you surround it with #pragma pack(push) #pragma pack(1) //your structure definition #pragma pack(pop) — Radu Chivu, Oct 21 '13 at 21:49
That does look equivalent, assuming m_Vertices is std::vector as you stated. If you can't spot anything, I'd add a test loop comparing your cubeData array with your m_Vertices vector to verify they're equivalent. — holtavolt, Oct 22 '13 at 03:19
Found the line causing the issue and it was in the next few lines of code that I didn't include. I'm editing the post now. I still don't know why it's causing the issue, but I've narrowed down the cause — Eric, Oct 22 '13 at 16:05

score 1 · Accepted Answer · answered Oct 22 '13 at 16:18

1

sizeof(m_Vertices) gives you the size of the vector object itself, not the number of elements it stores. What you probably want is m_Vertices.size() * sizeof(Vertex).

answered Oct 22 '13 at 16:18

ComicSansMS

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thank you! I'm converting from C# to c++ and I have trouble with these types of details – Eric Oct 22 '13 at 17:38
@Eric You might want to grab a [decent C++ textbook](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) on the way. C++ can be a lot of fun, but it can also be a royal pain if you try to cut corners while learning the basics. – ComicSansMS Oct 22 '13 at 18:25

DirectX Array of vertices draws, Vector of vertices does not draw

1 Answers1