【DX11地形篇】5-定向光照

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参考教程

Tutorial 4: Terrain Lighting

学习记录

  这篇文章中主要介绍对已经渲染的地形进行光照渲染（其实没什么新东西）。本篇代码基于上一篇，框架如下：

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  为地形添加光照，我们主要是需要在 TerrainClass 中计算法线，然后使用 LightShaderClass 代替 TextureShaderClass 渲染就行了。在 TerrainClass 中，我们修改顶点及模型等结构体为其添加法线的变量，然后新增一个计算法线的方法。修改后的 TerrainClass 声明如下：

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////////////////////////////////////////////////////////////////////////////////
// Class name: TerrainClass
////////////////////////////////////////////////////////////////////////////////
class TerrainClass
{
private:
	struct VertexType
	{
		XMFLOAT3 position;
		XMFLOAT2 texcoord;
		XMFLOAT3 normal;
	};

	struct HeightMapType {
		float x, y, z;
		float nx, ny, nz;
	};

	struct ModelType {
		float x, y, z;
		float tu, tv;
		float nx, ny, nz;
	};

	struct VectorType {
		float x, y, z;
	};

public:
	TerrainClass();
	TerrainClass(const TerrainClass&);
	~TerrainClass();

	bool Initialize(ID3D11Device* , char*);
	void Shutdown();
	bool Render(ID3D11DeviceContext*);

	int GetIndexCount();

private:
	bool InitializeBuffers(ID3D11Device*);
	void ShutdownBuffers();
	void RenderBuffers(ID3D11DeviceContext*);

	bool CalculateNormals();
	bool LoadSetupFile(CHAR*);
	bool LoadBitmapHeightMap();
	void ShutdownHeightMap();
	void SetTerrainCoordinates();
	bool BuildTerrainModel();
	void ShutdownTerrainModel();

private:
	ID3D11Buffer *m_vertexBuffer, *m_indexBuffer;
	int m_vertexCount, m_indexCount;

	int m_terrainHeight , m_terrainWidth;
	float m_heightScale;
	LPSTR m_terrainFilename;
	HeightMapType* m_heightMap;
	ModelType* m_terrainModel;
};

  法线计算方法如下：

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bool TerrainClass::CalculateNormals()
{
	int i, j, index1, index2, index3, index;
	float vertex1[3], vertex2[3], vertex3[3], vector1[3], vector2[3], sum[3], length;
	VectorType* normals;


	// Create a temporary array to hold the face normal vectors.
	normals = new VectorType[(m_terrainHeight-1) * (m_terrainWidth-1)];
	if(!normals)
	{
		return false;
	}

	// Go through all the faces in the mesh and calculate their normals.
	for(j=0; j<(m_terrainHeight-1); j++)
	{
		for(i=0; i<(m_terrainWidth-1); i++)
		{
			index1 = ((j+1) * m_terrainWidth) + i;      // Bottom left vertex.
			index2 = ((j+1) * m_terrainWidth) + (i+1);  // Bottom right vertex.
			index3 = (j * m_terrainWidth) + i;          // Upper left vertex.

			// Get three vertices from the face.
			vertex1[0] = m_heightMap[index1].x;
			vertex1[1] = m_heightMap[index1].y;
			vertex1[2] = m_heightMap[index1].z;

			vertex2[0] = m_heightMap[index2].x;
			vertex2[1] = m_heightMap[index2].y;
			vertex2[2] = m_heightMap[index2].z;

			vertex3[0] = m_heightMap[index3].x;
			vertex3[1] = m_heightMap[index3].y;
			vertex3[2] = m_heightMap[index3].z;

			// Calculate the two vectors for this face.
			vector1[0] = vertex1[0] - vertex3[0];
			vector1[1] = vertex1[1] - vertex3[1];
			vector1[2] = vertex1[2] - vertex3[2];
			vector2[0] = vertex3[0] - vertex2[0];
			vector2[1] = vertex3[1] - vertex2[1];
			vector2[2] = vertex3[2] - vertex2[2];

			index = (j * (m_terrainWidth - 1)) + i;

			// Calculate the cross product of those two vectors to get the un-normalized value for this face normal.
			normals[index].x = (vector1[1] * vector2[2]) - (vector1[2] * vector2[1]);
			normals[index].y = (vector1[2] * vector2[0]) - (vector1[0] * vector2[2]);
			normals[index].z = (vector1[0] * vector2[1]) - (vector1[1] * vector2[0]);

			// Calculate the length.
			length = (float)sqrt((normals[index].x * normals[index].x) + (normals[index].y * normals[index].y) + 
								 (normals[index].z * normals[index].z));

			// Normalize the final value for this face using the length.
			normals[index].x = (normals[index].x / length);
			normals[index].y = (normals[index].y / length);
			normals[index].z = (normals[index].z / length);
		}
	}

	// Now go through all the vertices and take a sum of the face normals that touch this vertex.
	for(j=0; j<m_terrainHeight; j++)
	{
		for(i=0; i<m_terrainWidth; i++)
		{
			// Initialize the sum.
			sum[0] = 0.0f;
			sum[1] = 0.0f;
			sum[2] = 0.0f;

			// Bottom left face.
			if(((i-1) >= 0) && ((j-1) >= 0))
			{
				index = ((j-1) * (m_terrainWidth-1)) + (i-1);

				sum[0] += normals[index].x;
				sum[1] += normals[index].y;
				sum[2] += normals[index].z;
			}

			// Bottom right face.
			if((i<(m_terrainWidth-1)) && ((j-1) >= 0))
			{
				index = ((j - 1) * (m_terrainWidth - 1)) + i;

				sum[0] += normals[index].x;
				sum[1] += normals[index].y;
				sum[2] += normals[index].z;
			}

			// Upper left face.
			if(((i-1) >= 0) && (j<(m_terrainHeight-1)))
			{
				index = (j * (m_terrainWidth-1)) + (i-1);

				sum[0] += normals[index].x;
				sum[1] += normals[index].y;
				sum[2] += normals[index].z;
			}

			// Upper right face.
			if((i < (m_terrainWidth-1)) && (j < (m_terrainHeight-1)))
			{
				index = (j * (m_terrainWidth-1)) + i;

				sum[0] += normals[index].x;
				sum[1] += normals[index].y;
				sum[2] += normals[index].z;
			}

			// Calculate the length of this normal.
			length = (float)sqrt((sum[0] * sum[0]) + (sum[1] * sum[1]) + (sum[2] * sum[2]));

			// Get an index to the vertex location in the height map array.
			index = (j * m_terrainWidth) + i;

			// Normalize the final shared normal for this vertex and store it in the height map array.
			m_heightMap[index].nx = (sum[0] / length);
			m_heightMap[index].ny = (sum[1] / length);
			m_heightMap[index].nz = (sum[2] / length);
		}
	}

	// Release the temporary normals.
	delete [] normals;
	normals = 0;

	return true;
}

  除此之外，我们在 ShaderManagerClass 里新增 LightShaderClass 的对象，以及在 ZoneClass 里新增 LightClass 的对象，然后修改渲染的方式就可以了。

  最终效果如下：

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  有光照的情况下我们的地形显得更加真实，源代码地址：DX11TerrainTutorial-TerrainLight

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