Learn OpenGL （十一）：光照貼圖
阿新 • • 發佈：2018-12-08
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。但這次我們會將紋理儲存為Material結構體中的一個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。
注意sampler2D是所謂的不透明型別(Opaque Type)，也就是說我們不能將它例項化，只能通過uniform來定義它。如果我們使用除uniform以外的方法（比如函式的引數）例項化這個結構體，GLSL會丟擲一些奇怪的錯誤。這同樣也適用於任何封裝了不透明型別的結構體。
我們也移除了環境光材質顏色向量，因為環境光顏色在幾乎所有情況下都等於漫反射顏色，所以我們不需要將它們分開儲存：
struct Material { sampler2D diffuse; vec3 specular; float shininess; }; ... in vec2 TexCoords;
如果你非常固執，仍想將環境光顏色設定為一個（漫反射值之外）不同的值，你也可以保留這個環境光的vec3，但整個物體仍只能擁有一個環境光顏色。如果想要對不同片段有不同的環境光值，你需要對環境光值單獨使用另外一個紋理。
注意我們將在片段著色器中再次需要紋理座標，所以我們宣告一個額外的輸入變數。接下來我們只需要從紋理中取樣片段的漫反射顏色值即可：
vec3 diffuse = light.diffuse * diff * vec3(texture(material.diffuse, TexCoords));
不要忘記將環境光得材質顏色設定為漫反射材質顏色同樣的值。
vec3 ambient = light.ambient * vec3(texture(material.diffuse, TexCoords));
這就是使用漫反射貼圖的全部步驟了。你可以看到，這並不是什麼新的東西，但這能夠極大地提高視覺品質。為了讓它正常工作，我們還需要使用紋理座標更新頂點資料，將它們作為頂點屬性傳遞到片段著色器，載入材質並繫結材質到合適的紋理單元。
更新後的頂點資料可以在這裡找到。頂點資料現在包含了頂點位置、法向量和立方體頂點處的紋理座標。讓我們更新頂點著色器來以頂點屬性的形式接受紋理座標，並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VAO的頂點屬性指標來匹配新的頂點資料，並載入箱子影象為一個紋理。在繪製箱子之前，我們希望將要用的紋理單元賦值到material.diffuse這個uniform取樣器，並繫結箱子的紋理到這個紋理單元：
lightingShader.setInt("material.diffuse", 0);
...
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, diffuseMap);
使用了漫反射貼圖之後，細節再一次得到驚人的提升，這次箱子有了光照開始閃閃發光（字面意思也是）了。你的箱子看起來可能像這樣：
#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/filesystem.h>
#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>
#include <iostream>
// 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);
// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
glfwSetWindowShouldClose(window, true);
if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
camera.ProcessKeyboard(FORWARD, deltaTime);
if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
camera.ProcessKeyboard(BACKWARD, deltaTime);
if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
camera.ProcessKeyboard(LEFT, deltaTime);
if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
camera.ProcessKeyboard(RIGHT, deltaTime);
}
// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
// make sure the viewport matches the new window dimensions; note that width and
// height will be significantly larger than specified on retina displays.
glViewport(0, 0, width, height);
}
// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
if (firstMouse)
{
lastX = xpos;
lastY = ypos;
firstMouse = false;
}
float xoffset = xpos - lastX;
float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top
lastX = xpos;
lastY = ypos;
camera.ProcessMouseMovement(xoffset, yoffset);
}
// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
camera.ProcessMouseScroll(yoffset);
}
// utility function for loading a 2D texture from file
// ---------------------------------------------------
unsigned int loadTexture(char const * path)
{
unsigned int textureID;
glGenTextures(1, &textureID);
int width, height, nrComponents;
unsigned char *data = stbi_load(path, &width, &height, &nrComponents, 0);
if (data)
{
GLenum format;
if (nrComponents == 1)
format = GL_RED;
else if (nrComponents == 3)
format = GL_RGB;
else if (nrComponents == 4)
format = GL_RGBA;
glBindTexture(GL_TEXTURE_2D, textureID);
glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
glGenerateMipmap(GL_TEXTURE_2D);
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_LINEAR);
stbi_image_free(data);
}
else
{
std::cout << "Texture failed to load at path: " << path << std::endl;
stbi_image_free(data);
}
return textureID;
}
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);
// glfw window creation
GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
glfwMakeContextCurrent(window);
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
glfwSetCursorPosCallback(window, mouse_callback);
glfwSetScrollCallback(window, scroll_callback);
// tell GLFW to capture our mouse
glfwSetInputMode(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("4.2.lighting_maps.vs", "4.2.lighting_maps.fs");
Shader lampShader("4.2.lamp.vs", "4.2.lamp.fs");
// set up vertex data (and buffer(s)) and configure vertex attributes
float vertices[] = {
// positions // normals // texture coords
-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
};
// first, configure the cube's VAO (and VBO)
unsigned int VBO, cubeVAO;
glGenVertexArrays(1, &cubeVAO);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindVertexArray(cubeVAO);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
glEnableVertexAttribArray(1);
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
glEnableVertexAttribArray(2);
// second, configure the light's VAO (VBO stays the same; the vertices are the same for the light object which is also a 3D cube)
unsigned int lightVAO;
glGenVertexArrays(1, &lightVAO);
glBindVertexArray(lightVAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
// note that we update the lamp's position attribute's stride to reflect the updated buffer data
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// load textures (we now use a utility function to keep the code more organized)
unsigned int diffuseMap = loadTexture(FileSystem::getPath("resources/textures/container2.png").c_str());
unsigned int specularMap = loadTexture(FileSystem::getPath("resources/textures/container2_specular.png").c_str());
// shader configuration
lightingShader.use();
lightingShader.setInt("material.diffuse", 0);
lightingShader.setInt("material.specular", 1);
// render loop
while (!glfwWindowShouldClose(window))
{
// per-frame time logic
float currentFrame = glfwGetTime();
deltaTime = currentFrame - lastFrame;
lastFrame = currentFrame;
// input
processInput(window);
// render
glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// be sure to activate shader when setting uniforms/drawing objects
lightingShader.use();
lightingShader.setVec3("light.position", lightPos);
lightingShader.setVec3("viewPos", camera.Position);
// light properties
lightingShader.setVec3("light.ambient", 0.2f, 0.2f, 0.2f);
lightingShader.setVec3("light.diffuse", 0.5f, 0.5f, 0.5f);
lightingShader.setVec3("light.specular", 1.0f, 1.0f, 1.0f);
// material properties
lightingShader.setFloat("material.shininess", 64.0f);
// view/projection transformations
glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
glm::mat4 view = camera.GetViewMatrix();
lightingShader.setMat4("projection", projection);
lightingShader.setMat4("view", view);
// world transformation
glm::mat4 model;
lightingShader.setMat4("model", model);
// bind diffuse map
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, diffuseMap);
// bind specular map
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, specularMap);
// render the cube
glBindVertexArray(cubeVAO);
glDrawArrays(GL_TRIANGLES, 0, 36);
// also draw the lamp object
lampShader.use();
lampShader.setMat4("projection", projection);
lampShader.setMat4("view", view);
model = glm::mat4();
model = glm::translate(model, lightPos);
model = glm::scale(model, glm::vec3(0.2f)); // a smaller cube
lampShader.setMat4("model", model);
glBindVertexArray(lightVAO);
glDrawArrays(GL_TRIANGLES, 0, 36);
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
glfwSwapBuffers(window);
glfwPollEvents();
}
// optional: de-allocate all resources once they've outlived their purpose:
glDeleteVertexArrays(1, &cubeVAO);
glDeleteVertexArrays(1, &lightVAO);
glDeleteBuffers(1, &VBO);
// glfw: terminate, clearing all previously allocated GLFW resources.
glfwTerminate();
return 0;
}如果新增一個叫做放射光貼圖(Emission Map)的東西，它是一個儲存了每個片段的發光值(Emission Value)的貼圖。發光值是一個包含（假設）光源的物體發光(Emit)時可能顯現的顏色，這樣的話物體就能夠忽略光照條件進行發光(Glow)。遊戲中某個物體在發光的時候，你通常看到的就是放射光貼圖。將這個紋理（作者為 creativesam）作為放射光貼圖新增到箱子上，需要新增的程式碼有：
cpp
片元著色器：
#version 330 core
out vec4 FragColor;
struct Material {
sampler2D diffuse;
sampler2D specular;
sampler2D emission;
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()
{
// 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;
// emission
vec3 emission = texture(material.emission, TexCoords).rgb;
vec3 result = ambient + diffuse + specular + emission;
FragColor = vec4(result, 1.0);
} 