对DX的顶点声明进行封装

创建顶点声明比较麻烦，下面的类封装了顶点声明

class VertexDeclaration
{
public:
	enum
	{
		Element_Pos = 0,
		Element_Normal,
		Element_TexCoord
	};
public:
	VertexDeclaration();
	virtual ~VertexDeclaration();
public:
	void CreateDecl(const int *elems, int len, bool useVec4 = false);
	IDirect3DVertexDeclaration9 * GetDecl();
protected:
	void SetVertexElement(D3DVERTEXELEMENT9 &e, BYTE type, BYTE usage);
protected:
	IDirect3DVertexDeclaration9 *mDecl;

	std::vector<D3DVERTEXELEMENT9> mElements;
};

VertexDeclaration::VertexDeclaration()
{
	mDecl = NULL;
}

VertexDeclaration::~VertexDeclaration()
{
	SAFE_RELEASE(mDecl);
}

void VertexDeclaration::CreateDecl(const int *elems, int len, bool useVec4)
{
	if (mDecl != NULL)
		return;

	WORD offset = 0;
	for (int i = 0; i < len; ++i)
	{
		D3DVERTEXELEMENT9 e;
		BYTE type = 0;
		BYTE usage = 0;

		if (i == 0)
			e.Offset = 0;
		else
			e.Offset = offset;

		if (elems[i] == Element_Pos)
		{
			if (useVec4)
			{
				type = D3DDECLTYPE_FLOAT4;
				offset += sizeof(float) * 4;
			}
			else
			{
				type = D3DDECLTYPE_FLOAT3;
				offset += sizeof(float) * 3;
			}

			usage = D3DDECLUSAGE_POSITION;
		}
		else if (elems[i] == Element_Normal)
		{
			type = D3DDECLTYPE_FLOAT3;
			usage = D3DDECLUSAGE_NORMAL;

			offset += sizeof(float) * 2;
		}
		else if (elems[i] == Element_TexCoord)
		{
			type = D3DDECLTYPE_FLOAT2;
			usage = D3DDECLUSAGE_TEXCOORD;

			offset += sizeof(float) * 2;
		}
		else
		{
			assert(false);
		}

		SetVertexElement(e, type, usage);
		mElements.push_back(e);
	}

	// 加上结束标记
	D3DVERTEXELEMENT9 end = D3DDECL_END();
	mElements.push_back(end);
	
	gDevice->CreateVertexDeclaration((const D3DVERTEXELEMENT9 *) &mElements[0], &mDecl);
}

IDirect3DVertexDeclaration9 * VertexDeclaration::GetDecl()
{
	return mDecl;
}

void VertexDeclaration::SetVertexElement(D3DVERTEXELEMENT9 &e, BYTE type, BYTE usage)
{
	e.Stream = 0;
	e.Method = D3DDECLMETHOD_DEFAULT;
	e.UsageIndex = 0;

	e.Type = type;
	e.Usage = usage;
}

使用

const int elements[] =
	{
		VertexDeclaration::Element_Pos,
		VertexDeclaration::Element_Normal,
		VertexDeclaration::Element_TexCoord,
		VertexDeclaration::Element_TexCoord
	};
	mDecl.CreateDecl(elements, sizeof(elements) / sizeof(int), false);