OpenGL学习笔记(八)-光照

光照

在上一节我们实现了材质.

材质用于表征一个表面的各种属性.

但是相同的材质在不同光照的情况下显现出的结果不同.例如:一件白衣服在不同灯光下显现的颜色不同.

所以最终像素点上的颜色应该由光照和材质共同决定.

光照模型有很多种,常见的有Phong光照模型,Blinn-Phong光照模型.
我们在这一节实现一个Blinn-Phong光照模型.

Light类

首先我们定义一个Light类,用于描述光源.

class Light
{
public:
    glm::vec3 position;
    glm::vec3 color;
    float radiant;

public:
    Light(){
        position = glm::vec3(0.0f, 0.0f, 0.0f);
        color = glm::vec3(1.0f, 1.0f, 1.0f);
        radiant = 10.0f;
    }
    Light(glm::vec3 pos, glm::vec3 col, float rad) {
        position = pos;
        color = col;
        radiant = rad;
    }
    ~Light() {}
};

现实生活中的光源很多,最常见的就是太阳光,灯光.

其中太阳光是一种平行光,我们定义一个平行光

#pragma once

#include "Light/Light.hpp"

class DirectionalLight : public Light
{
public:
    glm::vec3 direction;

public:
    DirectionalLight()
    : Light()
    {
        direction = glm::vec3(0.0f, -1.0f, 0.0f);
    }

    DirectionalLight(glm::vec3 direction)
    : Light()
    {
        this->direction = glm::normalize(direction);
    }

    DirectionalLight(glm::vec3 direction,glm::vec3 position, glm::vec3 color, float radiant)
    :Light(position, color, radiant)
    {
        this->direction = glm::normalize(direction);
    }

    ~DirectionalLight(){}
};

另外我们还可以定义点光源,但这里先按下不表.

Fragment Shader

我们在Fragment Shader中定义光源

struct DirLight
{
    vec3 dir;
    vec3 color;
    vec3 radiant;
};
struct PointLight
{
    vec3 pos;
    vec3 color;
    vec3 radint;

    float constant;
    float linear;
    float quadratic;
};

#define NR_POINT_LIGHTS 4
uniform DirLight dirLight;   // 光源位置
uniform PointLight pointLight[NR_POINT_LIGHTS]; // 点光源位置

传递数据

我们定义了一个场景类用于管理所有物体,光源等.

在具体Material类中,我们传递光源数据给Shader

unsigned short directionalLightDirLoc = glGetUniformLocation(shader->shaderProgramID, "dirLight.dir");
unsigned short directionalLightColorLoc = glGetUniformLocation(shader->shaderProgramID, "dirLight.color");
unsigned short directionalLightRadiantLoc = glGetUniformLocation(shader->shaderProgramID, "dirLight.radiant");
glm::vec3 directionalLightDir = Singleton<Scene>::Instance().directionalLights.at(0)->direction;
glm::vec3 directionalLightColor = Singleton<Scene>::Instance().directionalLights.at(0)->color;
float directionalLightRadiant = Singleton<Scene>::Instance().directionalLights.at(0)->radiant;
glUniform3fv(directionalLightDirLoc, 1, glm::value_ptr(directionalLightDir));
glUniform3fv(directionalLightColorLoc, 1, glm::value_ptr(directionalLightColor));
glUniform1f(directionalLightRadiantLoc, directionalLightRadiant);

Blinn-Phong光照模型

Blinn-Phong光照模型是Phong光照模型的改进版本.

Phong光照模型认为光源是平行于视线的,而Blinn-Phong光照模型认为光源是平行于表面的.

Blinn-Phong光照模型的计算公式如下:

vec3 N = normalize(Normal); // 法向量
vec3 L = normalize(lightDir); // 光线方向
vec3 V = normalize(viewDir); // 视线方向
vec3 R = reflect(-L, N); // 反射向量

float diffuse = max(dot(N, L), 0.0); // 漫反射
float specular = pow(max(dot(R, V), 0.0), 32.0); // 镜面反射

vec3 ambient = vec3(0.1); // 环境光
vec3 diffuseColor = vec3(1.0, 1.0, 1.0); // 漫反射颜色
vec3 specularColor = vec3(1.0, 1.0, 1.0); // 镜面反射颜色

vec3 result = (ambient + diffuse * diffuseColor + specular * specularColor) * objectColor;

最终Shader

我们可以得出最终的Shader如下:

#version 330 core
struct DirLight
{
    vec3 dir;
    vec3 color;
    vec3 radiant;
};
struct PointLight
{
    vec3 pos;
    vec3 color;
    vec3 radint;

    float constant;
    float linear;
    float quadratic;
};

#define NR_POINT_LIGHTS 4

in vec3 modelNormal;
in vec3 worldPos;    // 世界坐标
in vec3 worldNormal;      // 法线
in vec2 uv;          // 纹理坐标

uniform DirLight dirLight;   // 光源位置
uniform PointLight pointLight[NR_POINT_LIGHTS]; // 点光源位置

uniform sampler2D albedo;   // 颜色纹理
uniform sampler2D metallic;  // 金属度纹理
uniform sampler2D roughness; // 粗糙度纹理
uniform sampler2D emission;  // 发光纹理
uniform sampler2D ao;        // 环境光遮蔽纹理

uniform vec3 viewPos;        // 观察者位置

out vec4 FragColor;          // 输出颜色

vec3 computeDirLight(DirLight light, vec3 norm, vec3 viewDir) {
    vec3 lightDir = normalize(-light.dir);
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = diff * light.color;
    
    vec3 halfDir = normalize(lightDir + viewDir);
    float spec = pow(max(dot(norm, halfDir), 0.0), 32.0);
    vec3 specular = spec * light.color;
    
    return diffuse + specular;
}

vec3 computePointLight(PointLight light, vec3 norm, vec3 fragPos, vec3 viewDir) {
    vec3 lightDir = normalize(light.pos - fragPos);
    float distance = length(light.pos - fragPos);
    float attenuation = 1.0 / (light.constant + light.linear * distance + light.quadratic * (distance * distance));
    
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = diff * light.color * attenuation;
    
    vec3 halfDir = normalize(lightDir + viewDir);
    float spec = pow(max(dot(norm, halfDir), 0.0), 32.0);
    vec3 specular = spec * light.color * attenuation;
    
    return diffuse + specular;
}

void main() {
    vec3 objectColor = texture(albedo, uv).rgb;
    vec3 norm = normalize(modelNormal);
    vec3 viewDir = normalize(viewPos - worldPos);
    
    // 环境光
    vec3 result = 0.1 * objectColor; 

    // 计算方向光源
    result += computeDirLight(dirLight, norm, viewDir);
    
    // 计算点光源
    // for (int i = 0; i < NR_POINT_LIGHTS; i++) {
    //     result += computePointLight(pointLight[i], norm, worldPos, viewDir);
    // }

    FragColor = vec4(result * objectColor, 1.0);
}

结果

运行,可以看到我们的角色在光照下的表现了.