3D编程：Environment Mapping

Environment Mapping

Texture cubes的另一种应用是environment mapping。Environment mapping也称为reflection mapping，用于近似模拟reflective surfaces（反光表面），比如汽车上的镀了一层金属物的保险杠。

Environment mapping的处理过程比skybox稍微复杂一些，因为需要计算光线与表面的反射向量。反射向量主要由view direction（限入射角向量）和表面的法向量计算得到。具体的公式如下：

R = I – 2 * N * (I N)

其中，I表示入射向量，N指表面的法向量。列表8.2列出了一种environment mapping effect的代码。

列表8.2 EnvironmentMapping.fx

#include "include\\Common.fxh"

/************* Resources *************/

cbuffer CBufferPerFrame
{
	float4 AmbientColor : AMBIENT <
		string UIName =  "Ambient Light";
		string UIWidget = "Color";
	> = {1.0f, 1.0f, 1.0f, 0.0f};

	float4 EnvColor : COLOR <
		string UIName =  "Environment Color";
		string UIWidget = "Color";
	> = {1.0f, 1.0f, 1.0f, 1.0f };

	float3 CameraPosition : CAMERAPOSITION < string UIWidget="None"; >;
}

cbuffer CBufferPerObject
{
	float4x4 WorldViewProjection : WORLDVIEWPROJECTION < string UIWidget="None"; >;
	float4x4 World : WORLD < string UIWidget="None"; >;

	float ReflectionAmount <
		string UIName =  "Reflection Amount";
		string UIWidget = "slider";
		float UIMin = 0.0;
		float UIMax = 1.0;
		float UIStep = 0.05;
	> = {0.5f};
}

Texture2D ColorTexture <
	string ResourceName = "default_color.dds";
	string UIName =  "Color Texture";
	string ResourceType = "2D";
>;

TextureCube EnvironmentMap <
	string UIName =  "Environment Map";
	string ResourceType = "3D";
>;

SamplerState TrilinearSampler
{
	Filter = MIN_MAG_MIP_LINEAR;
};

RasterizerState DisableCulling
{
	CullMode = NONE;
};

/************* Data Structures *************/

struct VS_INPUT
{
	float4 ObjectPosition : POSITION;
	float3 Normal : NORMAL;
	float2 TextureCoordinate : TEXCOORD;
};

struct VS_OUTPUT
{
	float4 Position : SV_Position;
	float2 TextureCoordinate : TEXCOORD0;
	float3 ReflectionVector : TEXCOORD1;
};

/************* Vertex Shader *************/

VS_OUTPUT vertex_shader(VS_INPUT IN)
{
	VS_OUTPUT OUT = (VS_OUTPUT)0;

	OUT.Position = mul(IN.ObjectPosition, WorldViewProjection);
	OUT.TextureCoordinate = get_corrected_texture_coordinate(IN.TextureCoordinate);

	float3 worldPosition = mul(IN.ObjectPosition, World).xyz;
	float3 incident = normalize(worldPosition - CameraPosition);
	float3 normal = normalize(mul(float4(IN.Normal, 0), World).xyz);

	// Reflection Vector for cube map: R = I - 2*N * (I.N)
	OUT.ReflectionVector = reflect(incident, normal);

	return OUT;
}

/************* Pixel Shader *************/

float4 pixel_shader(VS_OUTPUT IN) : SV_Target
{
	float4 OUT = (float4)0;

	float4 color = ColorTexture.Sample(TrilinearSampler, IN.TextureCoordinate);
	float3 ambient = get_vector_color_contribution(AmbientColor, color.rgb);
	float3 environment = EnvironmentMap.Sample(TrilinearSampler, IN.ReflectionVector).rgb;
	float3 reflection = get_vector_color_contribution(EnvColor, environment);

	OUT.rgb = lerp(ambient, reflection, ReflectionAmount);
	OUT.a = color.a;

	return OUT;
}

/************* Techniques *************/

technique10 main10
{
	pass p0
	{
		SetVertexShader(CompileShader(vs_4_0, vertex_shader()));
		SetGeometryShader(NULL);
		SetPixelShader(CompileShader(ps_4_0, pixel_shader()));

		SetRasterizerState(DisableCulling);
	}
}

更多精彩内容：http://www.bianceng.cnhttp://www.bianceng.cn/Programming/extra/

以上是小编为您精心准备的的内容，在的博客、问答、公众号、人物、课程等栏目也有的相关内容，欢迎继续使用右上角搜索按钮进行搜索string
， float
， environment
， 向量
， mapping
out
mapper、map、mapping是什么意思、mapping文件、3d mapping，以便于您获取更多的相关知识。