这一讲原理比较简单，代码也很容易实现，Blinn在Phong的基础上提了一个小点的优化，实现起来一共两三行代码，就名垂千古。牛逼的东西往往并不复杂，越是讲的云里雾里的听不懂，往往都很虚，没有实质。
一、原理
冯氏光照在逼近真实光照和性能之间做了很好的平衡，解决了绝大部分场景的需求，也存在一些细节问题。这一章节讲Blinn-Phong通过对冯氏光照做的一些优化。
冯氏光照的问题分析：
冯氏光照
图中地板光照边缘出现明显的断裂，过渡不自然。
光照模型
在上面左图中看到的物体颜色是OK的，但是在右边这种场景下渲染出来的效果和实际看到的效果少有区别，按照冯氏光照模型，视线方向和反射方向 > 90°，导致计算的反射光强度为0，反射角计算如下，< 0就取0
float spec = pow(max(dot(viewDir, reflectDir), 0.0), 32);
vec3 specular = specularStrength * spec * lightColor;
这里原教程没有说的太细致，按照自己的理解再深入点，参考材质一章，实际每个物体对镜面高光有不同的反应，有些物体会有明显的散射，形成一个有着更大半径的高光点，如下图所示，金材质的反光比橡胶(yellow rubber)更集中，高光(散射)半径小。
材质对散射的影响
2. Blinn-Phong算法原理
1977年，James F. Blinn在冯氏着色模型上加以拓展，引入了Blinn-Phong着色模型。环境光和漫反射光计算方式不变，反射光完全改了，优化了视线和反射夹角 > 90°的情况，原理如下：
Blinn-Phong反射光模型
算法完全不同，先求光照和视线夹角的中间向量（半程向量），用半程向量和法线向量点乘来求反射因子，glsl实现代码：
1）计算出半程向量，入射光 + 视线光向量(基本的向量加法求对角线)，再归一化；
2）求反射因子，和冯氏的差不多，点乘后进行幂运算
vec3 lightDir = normalize(lightPos - FragPos);
vec3 viewDir = normalize(viewPos - FragPos);
vec3 halfwayDir = normalize(lightDir + viewDir);
float spec = pow(max(dot(normal, halfwayDir), 0.0), shininess);
vec3 specular = lightColor * spec;
二、 实现效果
冯氏光照 vs Blinn-Phong
我自己本地参考实现的效果，PHONG 和 BLINN-PHONG并没有这么大区别，不知道原因。
blinn-phong
三、完整代码
.vs
#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aNormal;
layout (location = 2) in vec2 aTexCoords;
out VS_OUT {
vec3 FragPos;
vec3 Normal;
vec2 TexCoords;
} vs_out;
uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;
void main()
{
vs_out.FragPos = aPos;
vs_out.Normal = aNormal;
vs_out.TexCoords = aTexCoords;
gl_Position = projection * view * vec4(aPos, 1.0);
}
.fs
#version 330 core
out vec4 FragColor;
in VS_OUT {
vec3 FragPos;
vec3 Normal;
vec2 TexCoords;
} fs_in;
uniform sampler2D floorTexture;
uniform vec3 lightPos;
uniform vec3 viewPos;
uniform bool blinn;
void main()
{
vec3 color = texture(floorTexture, fs_in.TexCoords).rgb;
// ambient
vec3 ambient = 0.05 * color;
// diffuse
vec3 lightDir = normalize(lightPos - fs_in.FragPos);
vec3 normal = normalize(fs_in.Normal);
float diff = max(dot(lightDir, normal), 0.0);
vec3 diffuse = diff * color;
// specular
vec3 viewDir = normalize(viewPos - fs_in.FragPos);
vec3 reflectDir = reflect(-lightDir, normal);
float spec = 0.0;
if (blinn)
{
vec3 halfwayDir = normalize(lightDir + viewDir);
spec = pow(max(dot(normal, halfwayDir), 0.0), 32.0);
}
else
{
vec3 reflectDir = reflect(-lightDir, normal);
spec = pow(max(dot(viewDir, reflectDir), 0.0), 8.0);
}
vec3 specular = vec3(0.3) * spec;
FragColor = vec4(ambient + diffuse + specular, 1.0);
}
主工程
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include "Shader.h"
#include "camera.h"
#include "model.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);
unsigned int loadCubemap(vector<std::string> faces);
// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
bool blinn = false;
bool blinnKeyPressed = false;
// camera
Camera camera(glm::vec3(0.0f, 0.5f, 30.0f));
float lastX = (float)SCR_WIDTH / 2.0;
float lastY = (float)SCR_HEIGHT / 2.0;
bool firstMouse = true;
// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;
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, "天哥学opengl", 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 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;
}
// glPolygonMode(GL_FRONT_AND_BACK ,GL_LINE );
// configure global opengl state
// -----------------------------
glEnable(GL_DEPTH_TEST);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
// build and compile shaders
// -------------------------
Shader shader("1.colors.vs", "1.colors.fs");
float planeVertices[] = {
// positions // normals // texcoords
10.0f, -0.5f, 10.0f, 0.0f, 1.0f, 0.0f, 10.0f, 0.0f,
-10.0f, -0.5f, 10.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f,
-10.0f, -0.5f, -10.0f, 0.0f, 1.0f, 0.0f, 0.0f, 10.0f,
10.0f, -0.5f, 10.0f, 0.0f, 1.0f, 0.0f, 10.0f, 0.0f,
-10.0f, -0.5f, -10.0f, 0.0f, 1.0f, 0.0f, 0.0f, 10.0f,
10.0f, -0.5f, -10.0f, 0.0f, 1.0f, 0.0f, 10.0f, 10.0f
};
// plane VAO
unsigned int planeVAO, planeVBO;
glGenVertexArrays(1, &planeVAO);
glGenBuffers(1, &planeVBO);
glBindVertexArray(planeVAO);
glBindBuffer(GL_ARRAY_BUFFER, planeVBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(planeVertices), planeVertices, GL_STATIC_DRAW);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)0);
glEnableVertexAttribArray(1);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));
glEnableVertexAttribArray(2);
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));
glBindVertexArray(0);
unsigned int floorTexture = loadTexture("resource/wood.png");
shader.use();
shader.setInt("texture1", 0);
glm::vec3 lightPos(0.0f, 0.0f, 0.0f);
// render loop
// -----------
while (!glfwWindowShouldClose(window))
{
glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
float currentFrame = glfwGetTime();
deltaTime = currentFrame - lastFrame;
lastFrame = currentFrame;
processInput(window);
glm::mat4 projection = glm::perspective(glm::radians(45.0f), (float)SCR_WIDTH / (float)SCR_HEIGHT, 1.0f, 200.0f);
glm::mat4 view = camera.GetViewMatrix();
shader.use();
shader.setMat4("projection", projection);
shader.setMat4("view", view);
shader.setInt("blinn", blinn);
// floor
glBindVertexArray(planeVAO);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, floorTexture);
glDrawArrays(GL_TRIANGLES, 0, 6);
std::cout << (blinn ? "Blinn-Phong" : "Phong") << std::endl;
// 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, &planeVAO);
glDeleteBuffers(1, &planeVBO);
glfwTerminate();
return 0;
}
// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
bool startRecord = false;
void processInput(GLFWwindow *window)
{
if (glfwGetKey(window, GLFW_KEY_B) == GLFW_PRESS && !blinnKeyPressed) {
blinnKeyPressed = true;
blinn = !blinn;
}
if (glfwGetKey(window, GLFW_KEY_B) == GLFW_RELEASE)
{
blinnKeyPressed = false;
}
if (glfwGetKey(window, GLFW_KEY_Y))
{
std::cout << "Y" << std::endl;
startRecord = true;
}
if (glfwGetKey(window, GLFW_KEY_N))
{
std::cout << "N" << std::endl;
startRecord = false;
}
if (startRecord) {
return;
}
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)
{
// std::cout << "xpos : " << xpos << std::endl;
// std::cout << "ypos : " << ypos << std::endl;
if (startRecord) {
return;
}
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;
// std::cout << "xoffset : " << xoffset << std::endl;
// std::cout << "yoffset : " << yoffset << std::endl;
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;
}
unsigned int loadCubemap(vector<std::string> faces)
{
unsigned int textureID;
glGenTextures(1, &textureID);
glBindTexture(GL_TEXTURE_CUBE_MAP, textureID);
int width, height, nrChannels;
for (unsigned int i = 0; i < faces.size(); i++) {
unsigned char *data = stbi_load(faces[i].c_str(), &width, &height, &nrChannels, 0);
if (data)
{
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);
stbi_image_free(data);
}
else
{
std::cout << "Cubemap texture failed to load at path: " << faces[i] << std::endl;
stbi_image_free(data);
}
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
}
return textureID;
}
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