我們需要拓展之前的系統(tǒng)，引入漫反射和鏡面光貼圖(Map)。這允許我們對(duì)物體的漫反射分量和鏡面光分量有著更精確的控制。

漫反射貼圖

我們希望通過(guò)某種方式對(duì)物體的每個(gè)片段單獨(dú)設(shè)置漫反射顏色。我們僅僅是對(duì)同樣的原理使用了不同的名字：其實(shí)都是使用一張覆蓋物體的圖像，讓我們能夠逐片段索引其獨(dú)立的顏色值。在光照?qǐng)鼍爸?，它通常叫做一個(gè)漫反射貼圖(Diffuse Map)（3D藝術(shù)家通常都這么叫它），它是一個(gè)表現(xiàn)了物體所有的漫反射顏色的紋理圖像。

在著色器中使用漫反射貼圖的方法和紋理教程中是完全一樣的。但這次我們會(huì)將紋理儲(chǔ)存為Material結(jié)構(gòu)體中的一個(gè)sampler2D。我們將之前定義的vec3漫反射顏色向量替換為漫反射貼圖。 

我們也移除了環(huán)境光材質(zhì)顏色向量，因?yàn)?strong>環(huán)境光顏色在幾乎所有情況下都等于漫反射顏色，所以我們不需要將它們分開(kāi)儲(chǔ)存：

struct Material {sampler2D diffuse;vec3      specular;float     shininess;
}; 
...
in vec2 TexCoords;

 注意我們將在片段著色器中再次需要紋理坐標(biāo)，所以我們聲明一個(gè)額外的輸入變量。接下來(lái)我們只需要從紋理中采樣片段的漫反射顏色值即可：

vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, TexCoords));

不要忘記將環(huán)境光的材質(zhì)顏色設(shè)置為漫反射材質(zhì)顏色同樣的值。

vec3 ambient = light.ambient * vec3(texture(material.diffuse, TexCoords));

就是使用漫反射貼圖的全部步驟了。你可以看到，這并不是什么新的東西，但這能夠極大地提高視覺(jué)品質(zhì)。為了讓它正常工作，我們還需要使用紋理坐標(biāo)更新頂點(diǎn)數(shù)據(jù)，將它們作為頂點(diǎn)屬性傳遞到片段著色器，加載材質(zhì)并綁定材質(zhì)到合適的紋理單元。

更新后的頂點(diǎn)數(shù)據(jù)可以在這里找到。頂點(diǎn)數(shù)據(jù)現(xiàn)在包含了頂點(diǎn)位置、法向量和立方體頂點(diǎn)處的紋理坐標(biāo)。讓我們更新頂點(diǎn)著色器來(lái)以頂點(diǎn)屬性的形式接受紋理坐標(biāo)，并將它們傳遞到片段著色器中：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;
layout (location = 2) in vec2 aTexCoords;
...
out vec2 TexCoords;void main()
{...TexCoords = aTexCoords;
}

記得去更新兩個(gè)VAO的頂點(diǎn)屬性指針來(lái)匹配新的頂點(diǎn)數(shù)據(jù)，并加載箱子圖像為一個(gè)紋理。在繪制箱子之前，我們希望將要用的紋理單元賦值到material.diffuse這個(gè)uniform采樣器，并綁定箱子的紋理到這個(gè)紋理單元：

lightingShader.setInt("material.diffuse", 0);
...
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, diffuseMap);

使用了漫反射貼圖之后，細(xì)節(jié)再一次得到驚人的提升，這次箱子有了光照開(kāi)始閃閃發(fā)光（字面意思也是）了。箱子看起來(lái)可能像這樣：

4.1.lighting_maps.vs

#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);
}

4.1.lighting_maps.fs

#version 330 core
out vec4 FragColor;struct Material {sampler2D diffuse;vec3 specular;    float shininess;
}; struct Light {vec3 position;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()
{// ambientvec3 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;  // specularvec3 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 * material.specular);  vec3 result = ambient + diffuse + specular;FragColor = vec4(result, 1.0);
} 

4.1.light_cube.vs

#version 330 core
layout (location = 0) in vec3 aPos;uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;void main()
{gl_Position = projection * view * model * vec4(aPos, 1.0);
}

4.1.light_cube.fs 

#version 330 core
out vec4 FragColor;void main()
{FragColor = vec4(1.0); // set all 4 vector values to 1.0
}

#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <stb_image.h>#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>#include <iostream>void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);
unsigned int loadTexture(const char *path);// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;// camera
Camera camera(glm::vec3(0.0f, 0.0f, 3.0f));
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;// lighting
glm::vec3 lightPos(1.2f, 1.0f, 2.0f);int main()
{// glfw: initialize and configure// ------------------------------glfwInit();glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);#ifdef __APPLE__glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif// glfw window creation// --------------------GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);if (window == NULL){std::cout << "Failed to create GLFW window" << std::endl;glfwTerminate();return -1;}glfwMakeContextCurrent(window);glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);glfwSetCursorPosCallback(window, mouse_callback);glfwSetScrollCallback(window, scroll_callback);// tell GLFW to capture our mouseglfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);// glad: load all OpenGL function pointers// ---------------------------------------if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){std::cout << "Failed to initialize GLAD" << std::endl;return -1;}// configure global opengl state// -----------------------------glEnable(GL_DEPTH_TEST);// build and compile our shader zprogram// ------------------------------------Shader lightingShader("4.1.lighting_maps.vs", "4.1.lighting_maps.fs");Shader lightCubeShader("4.1.light_cube.vs", "4.1.light_cube.fs");// set up vertex data (and buffer(s)) and configure vertex attributes// -----------------------------------------------------