概述
冯氏光照模型的主要结构由3个分量组成：环境(Ambient)、漫反射 (Diffuse)和镜面(Specular)光照
环境光照(Ambient Lighting)：物体几乎永远不会是完全黑暗的。所以环境光照一般是个常量
漫反射光照(Diffuse Lighting)：模拟光源对物体的方向性影响,物体的某一部分越是正对着光源，它就会越亮。
镜面光照(Specular Lighting)：模拟有光泽物体上面出现的亮点。镜面光照的颜色相比于物体的颜色会更倾向于光的颜色。
光照公式
最终片段颜色：环境颜色+漫反射颜色+镜面反射颜色
环境颜色 = 光源的环境光颜色 × 物体的环境材质颜色
漫反射颜色 = 光源的漫反射光颜色 × 物体的漫反射材质颜色 × 漫反射因子
DiffuseFactor = max(0, dot(N, L))
-
镜面反射颜色 = 光源的镜面光颜色 × 物体的镜面材质颜色 × 镜面反射因子
R=reflect(L, N)
SpecularFactor = power(max(0, dot(R,V)), shininess)
投光物
投光物主要有三种：定向光（太阳光）、点光（电灯泡）、聚光（手电筒）
以下是三种投光物对应的顶点着色器和片段着色器的实现。顶点着色器没有什么差别，它们的不同点体现在片段着色器。
顶点着色器
#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;
layout (location = 2) in vec2 aTexCoords;
out vec3 FragPos;
out vec3 Normal;
out vec2 TexCoords;
uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;
void main()
{
FragPos = vec3(model * vec4(aPos, 1.0));
Normal = mat3(transpose(inverse(model))) * aNormal;
TexCoords = aTexCoords;
gl_Position = projection * view * vec4(FragPos, 1.0);
}
1. 平行光
片段着色器
#version 330 core
out vec4 FragColor;
struct Material {
sampler2D diffuse;
sampler2D specular;
float shininess;
};
struct Light {
//vec3 position;
vec3 direction;
vec3 ambient;
vec3 diffuse;
vec3 specular;
};
in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoords;
uniform vec3 viewPos;
uniform Material material;
uniform Light light;
void main()
{
// ambient
vec3 ambient = light.ambient * texture(material.diffuse, TexCoords).rgb;
// diffuse
vec3 norm = normalize(Normal);
// vec3 lightDir = normalize(light.position - FragPos);
vec3 lightDir = normalize(-light.direction);
float diff = max(dot(norm, lightDir), 0.0);
vec3 diffuse = light.diffuse * diff * texture(material.diffuse, TexCoords).rgb;
// specular
vec3 viewDir = normalize(viewPos - FragPos);
vec3 reflectDir = reflect(-lightDir, norm);
float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
vec3 specular = light.specular * spec * texture(material.specular, TexCoords).rgb;
vec3 result = ambient + diffuse + specular;
FragColor = vec4(result, 1.0);
}
二 . 点光
- 光的衰减
随着光线传播距离的增长逐渐削减光的强度通常叫做衰减(Attenuation)。在现实世界中，灯在近处通常会非常亮，但随着距离的增加光源的亮度一开始会下降非常快，但在远处时剩余的光强度就会下降的非常缓慢了
第一列指定的是光所能覆盖的距离，第二、三、四列分别为 Kc、Kl 、 Kq
- 片段着色器
#version 330 core
out vec4 FragColor;
struct Material {
sampler2D diffuse;
sampler2D specular;
float shininess;
};
struct Light {
vec3 position;
vec3 ambient;
vec3 diffuse;
vec3 specular;
float constant;
float linear;
float quadratic;
};
in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoords;
uniform vec3 viewPos;
uniform Material material;
uniform Light light;
void main()
{
// ambient
vec3 ambient = light.ambient * texture(material.diffuse, TexCoords).rgb;
// diffuse
vec3 norm = normalize(Normal);
vec3 lightDir = normalize(light.position - FragPos);
float diff = max(dot(norm, lightDir), 0.0);
vec3 diffuse = light.diffuse * diff * texture(material.diffuse, TexCoords).rgb;
// specular
vec3 viewDir = normalize(viewPos - FragPos);
vec3 reflectDir = reflect(-lightDir, norm);
float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
vec3 specular = light.specular * spec * texture(material.specular, TexCoords).rgb;
// attenuation
float distance = length(light.position - FragPos);
float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));
ambient *= attenuation;
diffuse *= attenuation;
specular *= attenuation;
vec3 result = ambient + diffuse + specular;
FragColor = vec4(result, 1.0);
}
三. 聚光
- LightDir：从片段指向光源的向量。
- SpotDir：聚光所指向的方向。
- ϕ：指定了聚光半径的切光角。落在这个角度之外的物体都不会被这个聚光所照亮。
- θ：LightDir向量和SpotDir向量之间的夹角。在聚光内部的话θθ值应该比ϕϕ值小。
- 优化：平滑/软化边缘
需要模拟聚光有一个内圆锥(Inner Cone)和一个外圆锥(Outer Cone)
计算intensity ，在内圆锥与外圆锥之间平滑插值，内圆锥之内恒为1，外圆锥之外恒为0
float theta = dot(lightDir, normalize(-light.direction));
float epsilon = light.cutOff - light.outerCutOff;
float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);
...
// 将不对环境光做出影响，让它总是能有一点光
diffuse *= intensity;
specular *= intensity;
...
- 片段着色器
#version 330 core
out vec4 FragColor;
struct Material {
sampler2D diffuse;
sampler2D specular;
float shininess;
};
struct Light {
vec3 position;
vec3 direction;
float cutOff;
float outerCutOff;
vec3 ambient;
vec3 diffuse;
vec3 specular;
float constant;
float linear;
float quadratic;
};
in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoords;
uniform vec3 viewPos;
uniform Material material;
uniform Light light;
void main()
{
// ambient
vec3 ambient = light.ambient * texture(material.diffuse, TexCoords).rgb;
// diffuse
vec3 norm = normalize(Normal);
vec3 lightDir = normalize(light.position - FragPos);
float diff = max(dot(norm, lightDir), 0.0);
vec3 diffuse = light.diffuse * diff * texture(material.diffuse, TexCoords).rgb;
// specular
vec3 viewDir = normalize(viewPos - FragPos);
vec3 reflectDir = reflect(-lightDir, norm);
float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
vec3 specular = light.specular * spec * texture(material.specular, TexCoords).rgb;
// spotlight (soft edges)
float theta = dot(lightDir, normalize(-light.direction));
float epsilon = (light.cutOff - light.outerCutOff);
float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);
diffuse *= intensity;
specular *= intensity;
// attenuation
float distance = length(light.position - FragPos);
float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));
ambient *= attenuation;
diffuse *= attenuation;
specular *= attenuation;
vec3 result = ambient + diffuse + specular;
FragColor = vec4(result, 1.0);
}
四. 多光源
多光源指的是多个投光物同时存在于同一场景，这时对片段颜色的计算即是对多个投光物计算结果的累计叠加
#version 330 core
out vec4 FragColor;
struct Material {
sampler2D diffuse;
sampler2D specular;
float shininess;
};
struct DirLight {
vec3 direction;
vec3 ambient;
vec3 diffuse;
vec3 specular;
};
struct PointLight {
vec3 position;
float constant;
float linear;
float quadratic;
vec3 ambient;
vec3 diffuse;
vec3 specular;
};
struct SpotLight {
vec3 position;
vec3 direction;
float cutOff;
float outerCutOff;
float constant;
float linear;
float quadratic;
vec3 ambient;
vec3 diffuse;
vec3 specular;
};
#define NR_POINT_LIGHTS 4
in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoords;
uniform vec3 viewPos;
uniform DirLight dirLight;
uniform PointLight pointLights[NR_POINT_LIGHTS];
uniform SpotLight spotLight;
uniform Material material;
// function prototypes
vec3 CalcDirLight(DirLight light, vec3 normal, vec3 viewDir);
vec3 CalcPointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir);
vec3 CalcSpotLight(SpotLight light, vec3 normal, vec3 fragPos, vec3 viewDir);
void main()
{
// properties
vec3 norm = normalize(Normal);
vec3 viewDir = normalize(viewPos - FragPos);
// == =====================================================
// Our lighting is set up in 3 phases: directional, point lights and an optional flashlight
// For each phase, a calculate function is defined that calculates the corresponding color
// per lamp. In the main() function we take all the calculated colors and sum them up for
// this fragment's final color.
// == =====================================================
// phase 1: directional lighting
vec3 result = CalcDirLight(dirLight, norm, viewDir);
// phase 2: point lights
for(int i = 0; i < NR_POINT_LIGHTS; i++)
result += CalcPointLight(pointLights[i], norm, FragPos, viewDir);
// phase 3: spot light
result += CalcSpotLight(spotLight, norm, FragPos, viewDir);
FragColor = vec4(result, 1.0);
}
// calculates the color when using a directional light.
vec3 CalcDirLight(DirLight light, vec3 normal, vec3 viewDir)
{
vec3 lightDir = normalize(-light.direction);
// diffuse shading
float diff = max(dot(normal, lightDir), 0.0);
// specular shading
vec3 reflectDir = reflect(-lightDir, normal);
float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
// combine results
vec3 ambient = light.ambient * vec3(texture(material.diffuse, TexCoords));
vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, TexCoords));
vec3 specular = light.specular * spec * vec3(texture(material.specular, TexCoords));
return (ambient + diffuse + specular);
}
// calculates the color when using a point light.
vec3 CalcPointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
vec3 lightDir = normalize(light.position - fragPos);
// diffuse shading
float diff = max(dot(normal, lightDir), 0.0);
// specular shading
vec3 reflectDir = reflect(-lightDir, normal);
float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
// attenuation
float distance = length(light.position - fragPos);
float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));
// combine results
vec3 ambient = light.ambient * vec3(texture(material.diffuse, TexCoords));
vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, TexCoords));
vec3 specular = light.specular * spec * vec3(texture(material.specular, TexCoords));
ambient *= attenuation;
diffuse *= attenuation;
specular *= attenuation;
return (ambient + diffuse + specular);
}
// calculates the color when using a spot light.
vec3 CalcSpotLight(SpotLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
vec3 lightDir = normalize(light.position - fragPos);
// diffuse shading
float diff = max(dot(normal, lightDir), 0.0);
// specular shading
vec3 reflectDir = reflect(-lightDir, normal);
float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
// attenuation
float distance = length(light.position - fragPos);
float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));
// spotlight intensity
float theta = dot(lightDir, normalize(-light.direction));
float epsilon = light.cutOff - light.outerCutOff;
float intensity = clamp((theta - light.outerCutOff) / epsilon, 0.0, 1.0);
// combine results
vec3 ambient = light.ambient * vec3(texture(material.diffuse, TexCoords));
vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, TexCoords));
vec3 specular = light.specular * spec * vec3(texture(material.specular, TexCoords));
ambient *= attenuation * intensity;
diffuse *= attenuation * intensity;
specular *= attenuation * intensity;
return (ambient + diffuse + specular);
}
参考资料：
https://learnopengl-cn.github.io/02%20Lighting/05%20Light%20casters/
https://learnopengl-cn.github.io/02%20Lighting/06%20Multiple%20lights/
