GLSL 编程/Unity/平滑镜面高光
本教程介绍了逐像素光照（也称为Phong 着色）。
它基于“镜面高光”部分。如果您还没有阅读过本教程，请先阅读。逐顶点光照（即为每个顶点计算表面光照，然后插值顶点颜色）的主要缺点是质量有限，特别是对于镜面高光，如左侧图所示。解决方法是逐像素光照，它根据插值的法线向量为每个片段计算光照。虽然产生的图像质量明显更高，但性能成本也很高。
逐像素光照也称为 Phong 着色（与逐顶点光照形成对比，逐顶点光照也称为 Gouraud 着色）。这与 Phong 反射模型（也称为 Phong 光照）不同，Phong 反射模型通过环境、漫射和镜面项计算表面光照，如“镜面高光”部分中所述。
逐像素光照的关键思想很容易理解：法线向量和位置为每个片段插值，光照在片段着色器中计算。
除了优化之外，基于逐顶点光照的着色器代码实现逐像素光照非常简单：光照计算从顶点着色器移动到片段着色器，顶点着色器必须将光照计算所需的属性写入 varyings。然后片段着色器使用这些 varyings 来计算光照（而不是顶点着色器使用的属性）。就这么简单。
在本教程中，我们调整了“镜面高光”部分中的着色器代码以进行逐像素光照。结果如下所示
Shader "GLSL per-pixel lighting" {
Properties {
_Color ("Diffuse Material Color", Color) = (1,1,1,1)
_SpecColor ("Specular Material Color", Color) = (1,1,1,1)
_Shininess ("Shininess", Float) = 10
}
SubShader {
Pass {
Tags { "LightMode" = "ForwardBase" }
// pass for ambient light and first light source
GLSLPROGRAM
// User-specified properties
uniform vec4 _Color;
uniform vec4 _SpecColor;
uniform float _Shininess;
// The following built-in uniforms (except _LightColor0)
// are also defined in "UnityCG.glslinc",
// i.e. one could #include "UnityCG.glslinc"
uniform vec3 _WorldSpaceCameraPos;
// camera position in world space
uniform mat4 _Object2World; // model matrix
uniform mat4 _World2Object; // inverse model matrix
uniform vec4 _WorldSpaceLightPos0;
// direction to or position of light source
uniform vec4 _LightColor0;
// color of light source (from "Lighting.cginc")
varying vec4 position;
// position of the vertex in world space
varying vec3 varyingNormalDirection;
// surface normal vector in world space
#ifdef VERTEX
void main()
{
mat4 modelMatrix = _Object2World;
mat4 modelMatrixInverse = _World2Object; // unity_Scale.w
// is unnecessary because we normalize vectors
position = modelMatrix * gl_Vertex;
varyingNormalDirection = normalize(vec3(
vec4(gl_Normal, 0.0) * modelMatrixInverse));
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}
#endif
#ifdef FRAGMENT
void main()
{
vec3 normalDirection = normalize(varyingNormalDirection);
vec3 viewDirection =
normalize(_WorldSpaceCameraPos - vec3(position));
vec3 lightDirection;
float attenuation;
if (0.0 == _WorldSpaceLightPos0.w) // directional light?
{
attenuation = 1.0; // no attenuation
lightDirection = normalize(vec3(_WorldSpaceLightPos0));
}
else // point or spot light
{
vec3 vertexToLightSource =
vec3(_WorldSpaceLightPos0 - position);
float distance = length(vertexToLightSource);
attenuation = 1.0 / distance; // linear attenuation
lightDirection = normalize(vertexToLightSource);
}
vec3 ambientLighting =
vec3(gl_LightModel.ambient) * vec3(_Color);
vec3 diffuseReflection =
attenuation * vec3(_LightColor0) * vec3(_Color)
* max(0.0, dot(normalDirection, lightDirection));
vec3 specularReflection;
if (dot(normalDirection, lightDirection) < 0.0)
// light source on the wrong side?
{
specularReflection = vec3(0.0, 0.0, 0.0);
// no specular reflection
}
else // light source on the right side
{
specularReflection = attenuation * vec3(_LightColor0)
* vec3(_SpecColor) * pow(max(0.0, dot(
reflect(-lightDirection, normalDirection),
viewDirection)), _Shininess);
}
gl_FragColor = vec4(ambientLighting + diffuseReflection
+ specularReflection, 1.0);
}
#endif
ENDGLSL
}
Pass {
Tags { "LightMode" = "ForwardAdd" }
// pass for additional light sources
Blend One One // additive blending
GLSLPROGRAM
// User-specified properties
uniform vec4 _Color;
uniform vec4 _SpecColor;
uniform float _Shininess;
// The following built-in uniforms (except _LightColor0)
// are also defined in "UnityCG.glslinc",
// i.e. one could #include "UnityCG.glslinc"
uniform vec3 _WorldSpaceCameraPos;
// camera position in world space
uniform mat4 _Object2World; // model matrix
uniform mat4 _World2Object; // inverse model matrix
uniform vec4 _WorldSpaceLightPos0;
// direction to or position of light source
uniform vec4 _LightColor0;
// color of light source (from "Lighting.cginc")
varying vec4 position;
// position of the vertex in world space
varying vec3 varyingNormalDirection;
// surface normal vector in world space
#ifdef VERTEX
void main()
{
mat4 modelMatrix = _Object2World;
mat4 modelMatrixInverse = _World2Object; // unity_Scale.w
// is unnecessary because we normalize vectors
position = modelMatrix * gl_Vertex;
varyingNormalDirection = normalize(vec3(
vec4(gl_Normal, 0.0) * modelMatrixInverse));
gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
}
#endif
#ifdef FRAGMENT
void main()
{
vec3 normalDirection = normalize(varyingNormalDirection);
vec3 viewDirection =
normalize(_WorldSpaceCameraPos - vec3(position));
vec3 lightDirection;
float attenuation;
if (0.0 == _WorldSpaceLightPos0.w) // directional light?
{
attenuation = 1.0; // no attenuation
lightDirection = normalize(vec3(_WorldSpaceLightPos0));
}
else // point or spot light
{
vec3 vertexToLightSource =
vec3(_WorldSpaceLightPos0 - position);
float distance = length(vertexToLightSource);
attenuation = 1.0 / distance; // linear attenuation
lightDirection = normalize(vertexToLightSource);
}
vec3 diffuseReflection =
attenuation * vec3(_LightColor0) * vec3(_Color)
* max(0.0, dot(normalDirection, lightDirection));
vec3 specularReflection;
if (dot(normalDirection, lightDirection) < 0.0)
// light source on the wrong side?
{
specularReflection = vec3(0.0, 0.0, 0.0);
// no specular reflection
}
else // light source on the right side
{
specularReflection = attenuation * vec3(_LightColor0)
* vec3(_SpecColor) * pow(max(0.0, dot(
reflect(-lightDirection, normalDirection),
viewDirection)), _Shininess);
}
gl_FragColor =
vec4(diffuseReflection + specularReflection, 1.0);
}
#endif
ENDGLSL
}
}
// The definition of a fallback shader should be commented out
// during development:
// Fallback "Specular"
}
请注意，顶点着色器将归一化向量写入 varyingNormalDirection 以确保在插值中所有方向的权重相同。片段着色器再次将其归一化，因为插值后的方向不再归一化。
恭喜，现在您了解了逐像素 Phong 光照的工作原理。我们已经看到了
- 为什么逐顶点光照提供的质量有时不够（特别是由于镜面高光）。
- 逐像素光照的工作原理以及如何基于逐顶点光照的着色器实现它。
如果您还想了解有关逐顶点光照的着色器版本的更多信息
- 您应该阅读“镜面高光”部分。
除非另有说明，本页面上的所有示例源代码均为公共领域。