OpenGL基礎24：聚光燈

前置：OpenGL基礎23：平行光與點光源

一、聚光燈

三種基礎光源在上一章講了2種，現在只剩下聚光燈了

手電筒就是一個很經典例子，相對於點光源，聚光燈擁有以下特點

依然有衰減，但是聚光燈的光照一般都是非常強的（也就是有着非常遠的射程）
有一定的範圍，在這個範圍外光照極速衰減，距離聚光方向超過一定角度，哪怕離光源很近，也有可能完全沒有光照
依上，既有位置屬性，又有方向屬性（聚光方向）

相對於點光源，聚光燈會額外多出2個屬性：聚光方向和切光角

如下圖：其中 $\theta$ 就是入射光向量與聚光方向的夾角， $\phi$ 就是切光角，顯然

如果 $\theta$ 比 $\phi$ 大，那麼當前入射光的光強就可以直接忽略
在 $\phi$ 的範圍內，離光源越近，當前片段受到的光照就越強

目的很明顯了，求出 $cos{\theta}$ 和 $cos{\phi}$ 的大小

爲了方便測試，先把之前的光源扔了，然後我們假設自己頭上掛着個手電筒（就是以攝像機爲聚光燈，並且聚光中心爲我們視角的中央），着色器中再加入切光角和方向屬性

glUniform3f(lightPosLoc, camera.Position.x, camera.Position.y, camera.Position.z);
glUniform3f(lightDirect, camera.Front.x, camera.Front.y, camera.Front.z);
glUniform1f(lightCutOff, glm::cos(glm::radians(12.5f)));

vec3 lightDir = normalize(light.position - fragPosIn);
float theta = dot(lightDir, normalize(-light.direction));
if(theta > light.cutOff)        //兩個角度的餘弦角相比，餘弦值大的那個角度小
{
    //計算漫反射和鏡面反射
}
else
    //只考慮環境光

其實改動並不大，可以看到效果：

二、邊緣柔和

再看上面的效果，會感覺有點假，邊緣太過“鋒利”了，現實裏，它應該有一個漸變的效果

很容易想到插值，這樣的話就需要兩個角度，也就是兩個“切光角”：一個會給予一個聚光內圓錐，在內圓錐內的光強參數必定爲1，另一個給予一個聚光外圓錐，在外圓錐外的光強參數必定爲0（只有環境光），這樣就可以在兩個圓錐之間的那一小部分圓環內對光強進行插值，完美！

一樣，設 $\phi$ 爲內圓錐角， $\gamma$ 爲外圓錐角，我們就可以得出當前點的光強爲： $I = \frac{cos{\theta} - cos{\gamma}}{cos{\phi} - cos{\gamma}}$ ，其中保證其範圍在 (0, 1)內

完整代碼如下：

clamp(val, L, R)：確保val的值在 [L, R] 的範圍內

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 normal;
layout (location = 2) in vec2 texture;
out vec2 texIn;
out vec3 normalIn;
out vec3 fragPosIn;
uniform mat4 model;             //模型矩陣
uniform mat4 view;              //觀察矩陣
uniform mat4 projection;        //投影矩陣
void main()
{
    gl_Position = projection * view * model * vec4(position, 1.0);
    texIn = vec2(texture.x, 1.0f - texture.y);
    fragPosIn = vec3(model * vec4(position, 1.0f));
    normalIn = mat3(transpose(inverse(model))) * normal;
}

////////////////////////////////////////////////////////////////////////

#version 330 core
struct Material
{
    sampler2D diffuse;      //貼圖
    sampler2D specular;     //鏡面貼圖
    sampler2D emission;     //放射貼圖
    float shininess;        //反光度
};
struct Light
{
    vec3 position;
    vec3 direction;
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
    float k0, k1, k2;
    float cutOff, outCutOff;
};
uniform Material material;
uniform Light light;
out vec4 color;
uniform vec3 viewPos;
in vec2 texIn;
in vec3 fragPosIn;
in vec3 normalIn;
void main()
{
    //環境光
    vec3 ambient = light.ambient * vec3(texture(material.diffuse, texIn));

    vec3 diffuse = vec3(0.0f);
    vec3 specular = vec3(0.0f);
    float attenuation = 0;
    vec3 lightDir = normalize(light.position - fragPosIn);

    //聚光
    float theta = dot(lightDir, normalize(-light.direction));
    float lightSoft = clamp((theta - light.outCutOff) / (light.cutOff - light.outCutOff), 0.0f, 1.0f);

    //漫反射光
    vec3 norm = normalize(normalIn);
    float diff = max(dot(norm, lightDir), 0.0f);
    diffuse = light.diffuse * (diff * vec3(texture(material.diffuse, texIn)));

    //鏡面光
    vec3 viewDir = normalize(viewPos - fragPosIn);
    vec3 reflectDir = reflect(-lightDir, norm);
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
    specular = light.specular * (spec * vec3(texture(material.specular, texIn)));

    //點光源
    float dis = length(light.position - fragPosIn);
    attenuation = 1.0f / (light.k0 + light.k1 * dis + light.k2 * (dis * dis));

    //混合
    diffuse *= attenuation * lightSoft;
    specular *= attenuation * lightSoft;
    vec3 result = ambient + diffuse + specular;
    color = vec4(result, 1.0f);
}

main.cpp：

#include<iostream>
#include<opengl/glew.h>
#define GLEW_STATIC
#include<GLFW/glfw3.h>
#include"Camera.h"
#include<glm/glm.hpp>
#include<glm/gtc/matrix_transform.hpp>
#include<glm/gtc/type_ptr.hpp>
#include"Shader.h"
#include<opengl/freeglut.h>
#include<SOIL.h>

bool keys[1024];
Camera camera;
GLfloat lastX, lastY;
bool firstMouse = true;
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void cameraMove();
glm::vec3 lightPos(1.2f, 1.0f, 2.0f);
const GLuint WIDTH = 800, HEIGHT = 600;

int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

    GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr);
    glfwMakeContextCurrent(window);
    glfwSetKeyCallback(window, key_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);
    glewExperimental = GL_TRUE;
    glewInit();

    int width, height;
    glfwGetFramebufferSize(window, &width, &height);
    glViewport(0, 0, width, height);

    Shader shaderObj("ObjVShader.txt", "ObjFShader.txt");
    Shader shaderLight("LightVShader.txt", "LightFShader.txt");

    GLfloat vertices[] = 
    {
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,
         0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,  0.0f,  0.0f,

        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  1.0f,  1.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f,  0.0f,  0.0f,  1.0f,  0.0f,  0.0f,

        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f, -0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
        -0.5f, -0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f,  0.5f, -1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  0.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,  1.0f,  0.0f,

        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,
         0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  1.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
         0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,  0.0f,  1.0f,

        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f,
         0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  1.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
         0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  1.0f,  0.0f,
        -0.5f,  0.5f,  0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  0.0f,
        -0.5f,  0.5f, -0.5f,  0.0f,  1.0f,  0.0f,  0.0f,  1.0f
    };
    glm::vec3 position[] = 
    {
        glm::vec3(0.0f, -2.0f, 0.0f),
        glm::vec3(0.0f, -1.0f, 0.0f),
        glm::vec3(0.0f, 0.0f, 0.0f),
        glm::vec3(-2.0f, -2.0f, 0.0f),
        glm::vec3(-2.0f, -1.0f, 0.0f),
        glm::vec3(-3.0f, -2.0f, 0.0f),
        glm::vec3(-2.0f, -2.0f, 1.0f),
        glm::vec3(-1.0f, -2.0f, -4.0f),
    };
    GLuint VBO, VAO, textureA, textureB;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);

    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);

    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
    glEnableVertexAttribArray(2);

    int picWidth, picHeight;
    glGenTextures(1, &textureA);
    glBindTexture(GL_TEXTURE_2D, textureA);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    unsigned char* image = SOIL_load_image("Texture/wood2.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image);

    glGenTextures(1, &textureB);
    glBindTexture(GL_TEXTURE_2D, textureB);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST_MIPMAP_NEAREST);
    image = SOIL_load_image("Texture/specular.jpg", &picWidth, &picHeight, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, picWidth, picHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image);
    glBindTexture(GL_TEXTURE_2D, 0);

    shaderObj.Use();
    glUniform1i(glGetUniformLocation(shaderObj.Program, "material.diffuse"), 0);
    glUniform1i(glGetUniformLocation(shaderObj.Program, "material.specular"), 1);

    GLuint lightVAO;
    glGenVertexArrays(1, &lightVAO);
    glBindVertexArray(lightVAO);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
    //VBO數據已經綁定且我們就用之前的頂點數據，所以無需再管理VBO
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    glEnable(GL_DEPTH_TEST);
    while (!glfwWindowShouldClose(window))
    {
        glfwPollEvents();
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        glClear(GL_DEPTH_BUFFER_BIT);
        cameraMove();

        shaderLight.Use();
        lightPos.x = 1.0f + sin(glfwGetTime()) * 2.0f;
        lightPos.y = sin(glfwGetTime() / 2.0f) * 1.0f;
        glm::mat4 view = camera.GetViewMatrix();
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);
        glm::mat4 model = glm::translate(glm::mat4(1.0f), lightPos);
        model = glm::scale(model, glm::vec3(0.2f));
        GLint modelLoc = glGetUniformLocation(shaderLight.Program, "model");
        GLint viewLoc = glGetUniformLocation(shaderLight.Program, "view");
        GLint projLoc = glGetUniformLocation(shaderLight.Program, "projection");
        glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
        glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));

        //glBindVertexArray(lightVAO);
        //glDrawArrays(GL_TRIANGLES, 0, 36);


        shaderObj.Use();
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, textureA);
        glActiveTexture(GL_TEXTURE1);
        glBindTexture(GL_TEXTURE_2D, textureB);
        GLint matSpecularLoc = glGetUniformLocation(shaderObj.Program, "material.specular");
        GLint matShineLoc = glGetUniformLocation(shaderObj.Program, "material.shininess");
        glUniform3f(matSpecularLoc, 0.0f, 0.0f, 0.0f);
        glUniform1f(matShineLoc, 32.0f);

        GLint lightPosLoc = glGetUniformLocation(shaderObj.Program, "light.position");
        GLint lightAmbientLoc = glGetUniformLocation(shaderObj.Program, "light.ambient");
        GLint lightDiffuseLoc = glGetUniformLocation(shaderObj.Program, "light.diffuse");
        GLint lightSpecularLoc = glGetUniformLocation(shaderObj.Program, "light.specular");
        GLint lightK0 = glGetUniformLocation(shaderObj.Program, "light.k0");
        GLint lightK1 = glGetUniformLocation(shaderObj.Program, "light.k1");
        GLint lightK2 = glGetUniformLocation(shaderObj.Program, "light.k2");
        GLint lightCutOff = glGetUniformLocation(shaderObj.Program, "light.cutOff");
        GLint lightOutCutOff = glGetUniformLocation(shaderObj.Program, "light.outCutOff");
        GLint lightDirect = glGetUniformLocation(shaderObj.Program, "light.direction");
        glUniform3f(lightAmbientLoc, 0.2f, 0.2f, 0.2f);
        glUniform3f(lightDiffuseLoc, 1.0f, 1.0f, 1.0f);
        glUniform3f(lightSpecularLoc, 1.0f, 1.0f, 1.0f);
        glUniform1f(lightK0, 1.0f);
        glUniform1f(lightK1, 0.09f);
        glUniform1f(lightK2, 0.032f);
        glUniform3f(lightPosLoc, camera.Position.x, camera.Position.y, camera.Position.z);
        glUniform3f(lightDirect, camera.Front.x, camera.Front.y, camera.Front.z);
        glUniform1f(lightCutOff, glm::cos(glm::radians(12.5f)));
        glUniform1f(lightOutCutOff, glm::cos(glm::radians(15.0f)));

        GLint viewPosLoc = glGetUniformLocation(shaderObj.Program, "viewPos");
        glUniform3f(viewPosLoc, camera.Position.x, camera.Position.y, camera.Position.z);
        model = glm::mat4(1.0f);
        model = glm::rotate(model, glm::radians(57.0f), glm::vec3(-0.5f, 1.0f, 0.0f));
        modelLoc = glGetUniformLocation(shaderObj.Program, "model");
        viewLoc = glGetUniformLocation(shaderObj.Program, "view");
        projLoc = glGetUniformLocation(shaderObj.Program, "projection");
        glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
        glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));

        glBindVertexArray(VAO);
        for (int i = 0; i <= 7; i++)
        {
            model = glm::translate(glm::mat4(1.0f), position[i]);
            model = glm::rotate(model, glm::radians(0.0f), glm::vec3(-0.5f, 1.0f, 0.0f));
            glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
            glDrawArrays(GL_TRIANGLES, 0, 36);
        }

        glBindVertexArray(0);
        glfwSwapBuffers(window);
    }
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glfwTerminate();
    return 0;
}

GLfloat deltaTime = 0.0f;
GLfloat lastFrame = 0.0f;
void cameraMove()
{
    GLfloat currentFrame = glfwGetTime();
    deltaTime = currentFrame - lastFrame;
    lastFrame = currentFrame;

    GLfloat cameraSpeed = 1.0f * deltaTime;
    if (keys[GLFW_KEY_W])
        camera.ProcessKeyboard(Camera_Movement(FORWARD), deltaTime);
    if (keys[GLFW_KEY_S])
        camera.ProcessKeyboard(Camera_Movement(BACKWARD), deltaTime);
    if (keys[GLFW_KEY_A])
        camera.ProcessKeyboard(Camera_Movement(LEFT), deltaTime);
    if (keys[GLFW_KEY_D])
        camera.ProcessKeyboard(Camera_Movement(RIGHT), deltaTime);
}

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GL_TRUE);
    if (action == GLFW_PRESS)           //如果當前是按下操作
        keys[key] = true;
    else if (action == GLFW_RELEASE)            //鬆開鍵盤
        keys[key] = false;
}

void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}

void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }
    GLfloat xoffset = xpos - lastX;
    GLfloat yoffset = lastY - ypos;
    lastX = xpos;
    lastY = ypos;
    
    GLfloat sensitivity = 0.05;
    xoffset *= sensitivity;
    yoffset *= sensitivity;
    
    camera.ProcessMouseMovement(xoffset, yoffset);
}

OpenGL基礎24：聚光燈

一、聚光燈

二、邊緣柔和

OpenGL基礎28：模型

LuaForUnity9：uLua的一個簡單實例

LuaForUnity7：Lua“類與對象”

C#基礎14：泛型

OpenGL基礎27：網格

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