龙书11_chapter_6 二：HillsDemo解析

 书中HillsDemo 关键是类的结构，GeometryGenerator的组成和应用；

MeshData的构成，来存储Mesh的vertex和index数据；

class GeometryGenerator
{
public:
    struct Vertex
    {
        Vertex(){}
        Vertex(const XMFLOAT3& p):Position(p){}
        Vertex(float px,float py,float pz):Position(px,py,pz){}
        XMFLOAT3 Position;
    };
    struct MeshData
    {
        std::vector<Vertex> Vertices; //
        std::vector<UINT> Indices;   //
    };
    void CreateGrid(float width,float depth,UINT m,UINT n,MeshData &meshData);
    void CreateBox()...
    void Create_Other_Mesh()...
//...Create_Other_Mesh
};

GeometryGenerator.CPP文件中对CreateGrid进行具体操作，那么，怎么应用到具体vertexBuffer和indexBuffer中去呢？

首先是初始化中雷打不动的三个接口：

bool HillsApp::Init()
{
    if(!D3DApp::Init())
        return false;
    BuildGeometryBuffers();//Buffer
    BuildFX();//FX
    BuildVertexLayout();//Layout
    return true;
} 

void HillsApp::BuildGeometryBuffers()
{
    GeometryGenerator::MeshData grid;        //定义Hills的MeshData
    GeometryGenerator geoGen;
    geoGen.CreateGrid(160.0f, 160.0f, 50, 50, grid);//数据输入到MeshData
    mGridIndexCount = grid.Indices.size();
    // Extract the vertex elements we are interested and apply the height function to
    // each vertex.  In addition, color the vertices based on their height so we have
    // sandy looking beaches, grassy low hills, and snow mountain peaks.
    std::vector<Vertex> vertices(grid.Vertices.size()); //顶点数据的存储
    for(size_t i = 0; i < grid.Vertices.size(); ++i)
    {
        XMFLOAT3 p = grid.Vertices[i].Position;
        p.y = GetHeight(p.x, p.z);
        vertices[i].Pos   = p; 
        // Color the vertex based on its height.
        if( p.y < -10.0f )
        {
            // Sandy beach color.
            vertices[i].Color = XMFLOAT4(1.0f, 0.96f, 0.62f, 1.0f);
        }
        else if( p.y < 5.0f )
        {
            // Light yellow-green.
            vertices[i].Color = XMFLOAT4(0.48f, 0.77f, 0.46f, 1.0f);
        }
        else if( p.y < 12.0f )
        {
            // Dark yellow-green.
            vertices[i].Color = XMFLOAT4(0.1f, 0.48f, 0.19f, 1.0f);
        }
        else if( p.y < 20.0f )
        {
            // Dark brown.
            vertices[i].Color = XMFLOAT4(0.45f, 0.39f, 0.34f, 1.0f);
        }
        else
        {
            // White snow.
            vertices[i].Color = XMFLOAT4(1.0f, 1.0f, 1.0f, 1.0f);
        }
    }

    D3D11_BUFFER_DESC vbd;
    vbd.Usage = D3D11_USAGE_IMMUTABLE;      
    vbd.ByteWidth = sizeof(Vertex) * grid.Vertices.size();
    vbd.BindFlags = D3D11_BIND_VERTEX_BUFFER;
    vbd.CPUAccessFlags = 0;
    vbd.MiscFlags = 0;
    D3D11_SUBRESOURCE_DATA vinitData;
    vinitData.pSysMem = &vertices[0];       //找到Hills的顶点数据地址
    HR(md3dDevice->CreateBuffer(&vbd, &vinitData, &mVB)); //Hills数据给vertexBuffer
    // Pack the indices of all the meshes into one index buffer.
    D3D11_BUFFER_DESC ibd;
    ibd.Usage = D3D11_USAGE_IMMUTABLE;
    ibd.ByteWidth = sizeof(UINT) * mGridIndexCount;
    ibd.BindFlags = D3D11_BIND_INDEX_BUFFER;
    ibd.CPUAccessFlags = 0;
    ibd.MiscFlags = 0;
    D3D11_SUBRESOURCE_DATA iinitData;
    iinitData.pSysMem = &grid.Indices[0];
    HR(md3dDevice->CreateBuffer(&ibd, &iinitData, &mIB));
}

学习点：GeometryGenerator类的构成，以及对MeshData结构的应用。

           定义了MeshData这个子类，定义并实现了不同Mesh数据的接口，

          在应用中，CreateBuffer时候，定义相应的MeshData，获取不同Mesh的vertexData和IndexData