纹理坐标的探讨

顶点结构声明如下：

struct Vertex
{
	Vertex(){}
	Vertex(
		float x, float y, float z,
		float nx, float ny, float nz,
		float u, float v)
	{
		_x  = x;  _y  = y;  _z  = z;
		_nx = nx; _ny = ny; _nz = nz;
		_u  = u;  _v  = v;
	}
    float _x, _y, _z;
    float _nx, _ny, _nz;
    float _u, _v; // texture coordinates

	static const DWORD FVF;
};

　顶点信息如下：后两位为纹理坐标

    v[0] = Vertex(-2.0f, -2.0f ,2.0f,0.0f,0.0f,-1.0f,0.0f,1.0f);// ( 0.0f , 1.0f)
    v[1] = Vertex(-2.0f,  2.0f ,2.0f,0.0f,0.0f,-1.0f,0.0f,0.0f);// ( 0.0f , 0.0f)   
    v[2] = Vertex( 2.0f, -2.0f ,2.0f,0.0f,0.0f,-1.0f,1.0f,1.0f);// ( 1.0f , 1.0f)
    v[3] = Vertex( 2.0f,  2.0f ,2.0f,0.0f,0.0f,-1.0f,1.0f,0.0f);// ( 1.0f , 0.0f)

　纹理图如下：

运行结果如下，即完全显示。

再将纹理坐标改为

    v[0] = Vertex(-2.0f, -2.0f ,1.8f,0.0f,0.0f,-1.0f,0.0f,2.0f); // (0.0f,2.0f)
    v[1] = Vertex(-2.0f,  2.0f ,1.8f,0.0f,0.0f,-1.0f,0.0f,0.0f); // (0.0f,0.0f)
    v[2] = Vertex( 2.0f, -2.0f ,1.8f,0.0f,0.0f,-1.0f,2.0f,2.0f); // (2.0f,2.0f)
    v[3] = Vertex( 2.0f,  2.0f ,1.8f,0.0f,0.0f,-1.0f,2.0f,0.0f); // (2.0f,0.0f)

和

    v[0] = Vertex(-2.0f, -2.0f ,1.8f,0.0f,0.0f,-1.0f,0.0f,3.0f); // (0.0f,3.0f)
    v[1] = Vertex(-2.0f,  2.0f ,1.8f,0.0f,0.0f,-1.0f,0.0f,0.0f); // (0.0f,0.0f)
    v[2] = Vertex( 2.0f, -2.0f ,1.8f,0.0f,0.0f,-1.0f,3.0f,3.0f); // (3.0f,3.0f)
    v[3] = Vertex( 2.0f,  2.0f ,1.8f,0.0f,0.0f,-1.0f,3.0f,0.0f); // (3.0f,0.0f)

运行结果分别为：

纹理寻址模式为：重复寻址(wrap address mode) 默认这种模式

Device ->SetSamplerState(0,D3DSAMP_ADDRESSU,D3DPTADDRESSCAPS_WRAP);
Device ->SetSamplerState(0,D3DSAMP_ADDRESSV,D3DPTADDRESSCAPS_WRAP);