GLSL 程式設計/Unity/平滑鏡面高光
本教程介紹了逐畫素光照（也稱為Phong 著色）。
它基於“鏡面高光”部分。如果您還沒有閱讀過本教程，請先閱讀。逐頂點光照（即為每個頂點計算表面光照，然後插值頂點顏色）的主要缺點是質量有限，特別是對於鏡面高光，如左側圖所示。解決方法是逐畫素光照，它根據插值的法線向量為每個片段計算光照。雖然產生的影像質量明顯更高，但效能成本也很高。
逐畫素光照也稱為 Phong 著色（與逐頂點光照形成對比，逐頂點光照也稱為 Gouraud 著色）。這與 Phong 反射模型（也稱為 Phong 光照）不同，Phong 反射模型透過環境、漫射和鏡面項計算表面光照，如“鏡面高光”部分中所述。
逐畫素光照的關鍵思想很容易理解：法線向量和位置為每個片段插值，光照在片段著色器中計算。
除了最佳化之外，基於逐頂點光照的著色器程式碼實現逐畫素光照非常簡單：光照計算從頂點著色器移動到片段著色器，頂點著色器必須將光照計算所需的屬性寫入 varyings。然後片段著色器使用這些 varyings 來計算光照（而不是頂點著色器使用的屬性）。就這麼簡單。
在本教程中，我們調整了“鏡面高光”部分中的著色器程式碼以進行逐畫素光照。結果如下所示
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"
}
請注意，頂點著色器將歸一化向量寫入 varyingNormalDirection 以確保在插值中所有方向的權重相同。片段著色器再次將其歸一化，因為插值後的方向不再歸一化。
恭喜，現在您瞭解了逐畫素 Phong 光照的工作原理。我們已經看到了
- 為什麼逐頂點光照提供的質量有時不夠（特別是由於鏡面高光）。
- 逐畫素光照的工作原理以及如何基於逐頂點光照的著色器實現它。
如果您還想了解有關逐頂點光照的著色器版本的更多資訊
- 您應該閱讀“鏡面高光”部分。
除非另有說明，本頁面上的所有示例原始碼均為公共領域。