25.opengl高级光照-Gamma校正
2020-07-15 本文已影响0人
天叔
本章学习之前，先复习基础光照和材质的内容，光照的基础知识有些遗忘了，温故知新。
一、原理介绍
简单理解：人对光强度的感知是非线性的。亮度的范围如果是[0,1]，0是黑色，1是纯白色，那么0.5应该代表的是中间灰色吗？NO!!人能感知到的中间灰度值是亮度为0.2左右的光强。
这也符合人的正常感觉，人对光强逐步增加的初期感知非常强烈，好比，饥饿的人吃10个饼，并不是吃到第5、6个饼时饥饿感减少一半，是头几个饼吃充饥感最强。
既然人感觉到的中间亮度是0.2的光强，为了最大化利用内存，模拟人的感知特点，把0.2的光强设为中间值，用一半的颜色内存存放0到0.2中间的亮度。照相机实际上就是这么做的。而我们常规的显示器在解码颜色时，也会把经过处理后的颜色再还原回去，显示器默认颜色是经过非线性处理的。
为了适配显示器的对颜色的还原，纹理在渲染过程中就要做gamma校正。现在的显示器也可以自己设置gamma值。
注意！！！如果颜色内存足够大，不需要“合理”利用内存，就没有必要做亮度范围调整。
人对颜色的感知-图片来自知乎
gamma correction
原教程learnopgngl-Gamma校正对gamma校正的原理讲的不是太好，可能是作者自己太懂了，反而讲的略拗口。
参考知乎色彩校正中的 gamma 值是什么？循序渐进的理解比较易懂。
本章节实现效果：
未开启gamma校正的图像看起来整体偏暗些，经过gamma校正后，整体柔和一些，更逼近真实的场景。因为显示器会把低亮度的色值降下去。
未开启gamma校正
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开启gamma校正
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二、代码说明
1. 主程序增加4个光源
// -------------
glm::vec3 lightPositions[] = {
glm::vec3(-3.0f, 0.0f, 0.0f),
glm::vec3(-1.0f, 0.0f, 0.0f),
glm::vec3 (1.0f, 0.0f, 0.0f),
glm::vec3 (3.0f, 0.0f, 0.0f)
};
glm::vec3 lightColors[] = {
glm::vec3(0.25),
glm::vec3(0.50),
glm::vec3(0.75),
glm::vec3(1.00)
};
2. 顶点着色器没有特殊处理，主要看片段着色器
gamma校正算法很简单，用幂运算来模拟，color的每一个分量做1.0/2.2的幂次计算
片段着色器中的其他处理也值得学习，基本包含了一个完整的光照模型的大部分元素，后面还有少量的补充，比如阴影等细节
- 1）环境光照（这里没有）
- 2）漫反射
- 3）反射（BlinnPhong采用半程向量的反射优化）
- 4）gamma校正
vec3 BlinnPhong(vec3 normal, vec3 fragPos, vec3 lightPos, vec3 lightColor)
{
// diffuse
vec3 lightDir = normalize(lightPos - fragPos);
float diff = max(dot(lightDir, normal), 0.0);
vec3 diffuse = diff * lightColor;
// specular
vec3 viewDir = normalize(viewPos - fragPos);
vec3 reflectDir = reflect(-lightDir, normal);
float spec = 0.0;
vec3 halfwayDir = normalize(lightDir + viewDir);
spec = pow(max(dot(normal, halfwayDir), 0.0), 64.0);
vec3 specular = spec * lightColor;
// simpleattenuation
float max_distance = 1.5;
float distance = length(lightPos - fragPos);
float attenuation = 1.0 / (gamma ? distance * distance : distance);
diffuse *= attenuation;
specular *= attenuation;
return diffuse + specular;
}
void main()
{
vec3 color = texture(floorTexture, fs_in.TexCoords).rgb;
vec3 lighting = vec3(0.0);
for (int i = 0; i < 4; ++i) {
lighting += BlinnPhong(normalize(fs_in.Normal), fs_in.FragPos, lightPositions[i], lightColors[i]);
}
color *= lighting;
if(gamma)
{
color = pow(color, vec3(1.0 / 2.2));
}
FragColor = vec4(color, 1.0);
}
三、完整代码
主程序里，增加了按键 Y 和 N的处理优化，方便截屏记录笔记
1. 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);
}
2. fs
#version 330 core
out vec4 FragColor;
in VS_OUT {
vec3 FragPos;
vec3 Normal;
vec2 TexCoords;
} fs_in;
uniform sampler2D floorTexture;
uniform vec3 lightPositions[4];
uniform vec3 lightColors[4];
uniform vec3 viewPos;
uniform bool gamma;
vec3 BlinnPhong(vec3 normal, vec3 fragPos, vec3 lightPos, vec3 lightColor)
{
// diffuse
vec3 lightDir = normalize(lightPos - fragPos);
float diff = max(dot(lightDir, normal), 0.0);
vec3 diffuse = diff * lightColor;
// specular
vec3 viewDir = normalize(viewPos - fragPos);
vec3 reflectDir = reflect(-lightDir, normal);
float spec = 0.0;
vec3 halfwayDir = normalize(lightDir + viewDir);
spec = pow(max(dot(normal, halfwayDir), 0.0), 64.0);
vec3 specular = spec * lightColor;
// simpleattenuation
float max_distance = 1.5;
float distance = length(lightPos - fragPos);
float attenuation = 1.0 / (gamma ? distance * distance : distance);
diffuse *= attenuation;
specular *= attenuation;
return diffuse + specular;
}
void main()
{
vec3 color = texture(floorTexture, fs_in.TexCoords).rgb;
vec3 lighting = vec3(0.0);
for (int i = 0; i < 4; ++i) {
lighting += BlinnPhong(normalize(fs_in.Normal), fs_in.FragPos, lightPositions[i], lightColors[i]);
}
color *= lighting;
if(gamma)
{
color = pow(color, vec3(1.0 / 2.2));
}
FragColor = vec4(color, 1.0);
}
3. 主程序
#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;
bool gammaEnabled = false;
bool gammaKeyPressed = 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");
unsigned int floorTextureGammaCorrected = loadTexture("resource/wood.png");
shader.use();
shader.setInt("texture1", 0);
// lighting info
// -------------
glm::vec3 lightPositions[] = {
glm::vec3(-3.0f, 0.0f, 0.0f),
glm::vec3(-1.0f, 0.0f, 0.0f),
glm::vec3 (1.0f, 0.0f, 0.0f),
glm::vec3 (3.0f, 0.0f, 0.0f)
};
glm::vec3 lightColors[] = {
glm::vec3(0.25),
glm::vec3(0.50),
glm::vec3(0.75),
glm::vec3(1.00)
};
// 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);
//set light uniforms
glUniform3fv(glGetUniformLocation(shader.ID, "lightPositions"), 4, &lightPositions[0][0]);
glUniform3fv(glGetUniformLocation(shader.ID, "lightColors"), 4, &lightColors[0][0]);
shader.setVec3("viewPos", camera.Position);
shader.setInt("gamma", gammaEnabled);
// floor
glBindVertexArray(planeVAO);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, floorTexture);
glDrawArrays(GL_TRIANGLES, 0, 6);
std::cout << (gammaEnabled ? "Gamma enabled" : "Gamma disabled") << 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)
{
std::cout << "B state: " << glfwGetKey(window, GLFW_KEY_B) << std::endl;
if (glfwGetKey(window, GLFW_KEY_B) == GLFW_PRESS && !gammaKeyPressed)
{
std::cout << "press b--------------" << std::endl;
gammaEnabled = !gammaEnabled;
gammaKeyPressed = true;
}
if (glfwGetKey(window, GLFW_KEY_B) == GLFW_RELEASE)
{
std::cout << "release b" << std::endl;
gammaKeyPressed = false;
}
if (glfwGetKey(window, GLFW_KEY_Y))
{
std::cout << "Y" << std::endl;
startRecord = true;
firstMouse = 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;
}
