着色器(Shader)
9.4 着色器
着色器(Shader):在GPU伤的片段,执行图形渲染的各个阶段,决定最终像素的颜色和其他属性;可以分为顶点着色器(Vertex Shader)和片段着色器(Fragment Shader),着色器使用GLSL语言;
顶点着色器(Vertex Shader):顶点着色器主要负责处理输入的顶点坐标,并对这些顶点进行变换
片段着色器(Fragment Shader):主要负责处理图形中的每个片段(像素)。它可以计算像素的最终颜色,进行光照计算、纹理映射、颜色插值等
着色器的结构:版本声明 + 输入/输出/全局变量 + main函数
9.4.1 uniform变量
uniform 是一个全局的变量,在着色器glsl代码上只有变量声明,但是并没有具体值,这个变量的值一般在c pp上进行赋值;
void setVec3(const std::string &name, float x, float y, float z) const
{
glUniform3f(glGetUniformLocation(ID, name.c_str()), x, y, z);
}
glGetUniformLocation
函数获取指定名称的 uniform 变量在着色器程序中的位置。
使用 glUniform3f
函数将 vec3
类型的值设置给指定位置的 uniform 变量
9.4.2 Vertex Shader
#version 330 core //版本声明
//声明了两个输入属性,分别是顶点的位置和颜色
layout(location = 0) in vec3 aPosition;//顶点位置属性在顶点数据中的位置索引为0
in vec3 aColor;//颜色属性
out vec3 vColor;//传递顶点的颜色给片段着色器
//三个uniform变量,分别代表投影矩阵、视图矩阵和模型矩阵
uniform mat4 uProjection;//Uniform 是特殊的一种全局变量
uniform mat4 uView;
uniform mat4 uModel;
void main()
{
//顶点位置从对象空间变换到裁剪空间
gl_Position = uProjection * uView * uModel * vec4(aPosition, 1.0);
vColor = aColor;//将顶点的颜色属性传递给输出属性
}
这段代码简单地描述了一个典型的顶点着色器结构,它将顶点从对象空间变换到裁剪空间,并传递了顶点的颜色属性给片段着色器。
9.4.3 Fragment Shader
#version 330 core
in vec3 vColor; // 接收从顶点着色器传递过来的颜色属性
//片段着色器的输出颜色是一个 vec4 类型的向量,其中的分量分别对应着红、绿、蓝和透明度
out vec4 FragColor; // 片段着色器的输出颜色
void main()
{
FragColor = vec4(vColor, 1.0); // 使用顶点着色器传递的颜色属性作为片段的颜色输出
}
在这个示例中,片段着色器接收顶点着色器传递过来的颜色属性,并将其作为片段的颜色输出。
9.4.4 调用着色器
调用着色器的步骤:
创建: glCreateShader,glShaderSource
编译:glcompileShader,glGetShaderiv
链接使用:glCreateProgram,glAttachShader,glLinkProgram, glUseProgram,glGetProgramiv
while循环:glfwWindowShouldClose(),glClear,glfwSwapBuffers(),glfwPollEvents
清理:glDeleteShader,glDeleteProgram,glfwTerminate()
(1)创建
glCreateShader
作用:创建一个空的 shader 对象,并返回一个非0的shader ID值
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);//创建顶点着色器
glShaderSource
作用:给shader对象指定源码
原型:
void glShaderSource(GLuint shader, //需要设置源码的 shader 对象
GLsizei count,//源码脚本的数量
const GLchar **string,//shader的glsl代码对象
const GLint *length);//shader的glsl代码对象的长度,一般NULL表示代码结束的位置
// 创建顶点着色器对象
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
// 将顶点着色器源代码加载到着色器对象中
const char* vertexShaderSourcePtr = vertexShaderSource.c_str();
glShaderSource(vertexShader, 1, &vertexShaderSourcePtr, NULL);
(2)编译
glCompileShader
作用:编译着色器
glCompileShader(vertexShader);//编译顶点着色器
glGetShaderiv
作用:从着色器对象返回一个信息数组
void glGetShaderiv(GLuint shader,GLenum pname,GLint *params);
//指定着色器对象的参数,GL_COMPILE_STATUS:
//params:函数返回结果
使用:
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);//检查顶点着色器是否编译成功
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
glGetShaderInfoLog
作用:反回着色器对象的信息日志
char infoLog[512];
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
(3)链接
a. 在连接shader之前,首先要创建一个容纳程序的容器,称为着色器程序容器。通过glCreateProgram函数来创建一个程序容器。
函数原型:
int glCreateProgram () //如果函数调用成功将返回一个正整数作为该着色器程序的id。
b. shader容器添加到程序中,shader容器不一定需要被编译,甚至不需要包含任何的代码,lAttachShader函数将shader容器添加到程序中
函数原型:
void glAttachShader (int program, int shader)
/**
program是着色器程序容器的id;
shader是要添加的顶点或者片元shader容器的id
*/
参数含义:
program是着色器程序容器的id;
shader是要添加的顶点或者片元shader容器的id
c. 在链接操作执行以后,可以任意修改shader的源代码,对shader重新编译不会影响整个程序,除非重新链接程序。
函数原型:
void glLinkProgram (int program)
//program是着色器程序容器的id
d. 加载并使用链接好的程序,将program设置为0,表示使用固定功能管线。
函数原型:
void glUseProgram (int program)
//program是要使用的着色器程序的id
(4)while循环
// 渲染循环
while (!glfwWindowShouldClose(window)) {
glClear(GL_COLOR_BUFFER_BIT);//清除缓存,GL_COLOR_BUFFER_BIT 颜色缓存
// 绘制代码
glfwSwapBuffers(window);//交换缓冲区,渲染操作一般是在后缓冲区完成的,而前缓冲区则用于显示。调用这个函数会交换前后缓冲区的内容,使得后缓冲区的内容被复制到前缓冲区,从而显示在窗口中
glfwPollEvents();//挂起所有事件
}
(5)清理
// 清理资源
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
glDeleteProgram(shaderProgram);
glfwTerminate();
示例代码1:
#ifndef SHADER_H
#define SHADER_H
#include <glad/glad.h>
#include <glm/glm.hpp>
#include <string>
#include <fstream>
#include <sstream>
#include <iostream>
class Shader
{
public:
unsigned int ID;
// constructor generates the shader on the fly
// ------------------------------------------------------------------------
Shader(const char* vertexPath, const char* fragmentPath)
{
// 1. retrieve the vertex/fragment source code from filePath
std::string vertexCode;
std::string fragmentCode;
std::ifstream vShaderFile;
std::ifstream fShaderFile;
// ensure ifstream objects can throw exceptions:
vShaderFile.exceptions (std::ifstream::failbit | std::ifstream::badbit);
fShaderFile.exceptions (std::ifstream::failbit | std::ifstream::badbit);
try
{
// open files
vShaderFile.open(vertexPath);
fShaderFile.open(fragmentPath);
std::stringstream vShaderStream, fShaderStream;
// read file's buffer contents into streams
vShaderStream << vShaderFile.rdbuf();
fShaderStream << fShaderFile.rdbuf();
// close file handlers
vShaderFile.close();
fShaderFile.close();
// convert stream into string
vertexCode = vShaderStream.str();
fragmentCode = fShaderStream.str();
}
catch (std::ifstream::failure& e)
{
std::cout << "ERROR::SHADER::FILE_NOT_SUCCESSFULLY_READ: " << e.what() << std::endl;
}
const char* vShaderCode = vertexCode.c_str();
const char * fShaderCode = fragmentCode.c_str();
// 2. compile shaders
unsigned int vertex, fragment;
// vertex shader
vertex = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex, 1, &vShaderCode, NULL);
glCompileShader(vertex);
checkCompileErrors(vertex, "VERTEX");
// fragment Shader
fragment = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment, 1, &fShaderCode, NULL);
glCompileShader(fragment);
checkCompileErrors(fragment, "FRAGMENT");
// shader Program
ID = glCreateProgram();
glAttachShader(ID, vertex);
glAttachShader(ID, fragment);
glLinkProgram(ID);
checkCompileErrors(ID, "PROGRAM");
// delete the shaders as they're linked into our program now and no longer necessary
glDeleteShader(vertex);
glDeleteShader(fragment);
}
// activate the shader
// ------------------------------------------------------------------------
void use() const
{
glUseProgram(ID);
}
// utility uniform functions
// ------------------------------------------------------------------------
void setBool(const std::string &name, bool value) const
{
glUniform1i(glGetUniformLocation(ID, name.c_str()), (int)value);
}
// ------------------------------------------------------------------------
void setInt(const std::string &name, int value) const
{
glUniform1i(glGetUniformLocation(ID, name.c_str()), value);
}
// ------------------------------------------------------------------------
void setFloat(const std::string &name, float value) const
{
glUniform1f(glGetUniformLocation(ID, name.c_str()), value);
}
// ------------------------------------------------------------------------
void setVec2(const std::string &name, const glm::vec2 &value) const
{
glUniform2fv(glGetUniformLocation(ID, name.c_str()), 1, &value[0]);
}
void setVec2(const std::string &name, float x, float y) const
{
glUniform2f(glGetUniformLocation(ID, name.c_str()), x, y);
}
// ------------------------------------------------------------------------
void setVec3(const std::string &name, const glm::vec3 &value) const
{
glUniform3fv(glGetUniformLocation(ID, name.c_str()), 1, &value[0]);
}
void setVec3(const std::string &name, float x, float y, float z) const
{
glUniform3f(glGetUniformLocation(ID, name.c_str()), x, y, z);
}
// ------------------------------------------------------------------------
void setVec4(const std::string &name, const glm::vec4 &value) const
{
glUniform4fv(glGetUniformLocation(ID, name.c_str()), 1, &value[0]);
}
void setVec4(const std::string &name, float x, float y, float z, float w) const
{
glUniform4f(glGetUniformLocation(ID, name.c_str()), x, y, z, w);
}
// ------------------------------------------------------------------------
void setMat2(const std::string &name, const glm::mat2 &mat) const
{
glUniformMatrix2fv(glGetUniformLocation(ID, name.c_str()), 1, GL_FALSE, &mat[0][0]);
}
// ------------------------------------------------------------------------
void setMat3(const std::string &name, const glm::mat3 &mat) const
{
glUniformMatrix3fv(glGetUniformLocation(ID, name.c_str()), 1, GL_FALSE, &mat[0][0]);
}
// ------------------------------------------------------------------------
void setMat4(const std::string &name, const glm::mat4 &mat) const
{
glUniformMatrix4fv(glGetUniformLocation(ID, name.c_str()), 1, GL_FALSE, &mat[0][0]);
}
private:
// utility function for checking shader compilation/linking errors.
// ------------------------------------------------------------------------
void checkCompileErrors(GLuint shader, std::string type)
{
GLint success;
GLchar infoLog[1024];
if (type != "PROGRAM")
{
glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
if (!success)
{
glGetShaderInfoLog(shader, 1024, NULL, infoLog);
std::cout << "ERROR::SHADER_COMPILATION_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
}
}
else
{
glGetProgramiv(shader, GL_LINK_STATUS, &success);
if (!success)
{
glGetProgramInfoLog(shader, 1024, NULL, infoLog);
std::cout << "ERROR::PROGRAM_LINKING_ERROR of type: " << type << "\n" << infoLog << "\n -- --------------------------------------------------- -- " << std::endl;
}
}
}
};
#endif
示例代码2:
cmakelist
cmake_minimum_required(VERSION 3.12)
project(OpenGL)
set(CMAKE_CXX_STANDARD 11)
set(GLEW_H /usr/local/Cellar/glew/2.2.0_1/include/GL)
set(GLFW_H /usr/local/Cellar/glfw/3.3.6/include/GLFW)
set(GLAD_H /Users/xiongzhiyao/glad/include)
set(KH_H /Users/xiongzhiyao/glad/include/)
include_directories(${GLEW_H} ${GLFW_H} ${GLAD_H} ${KH_H})
# 添加目标链接
set(GLEW_LINK /usr/local/Cellar/glew/2.2.0_1/lib/libGLEW.2.2.dylib)
set(GLFW_LINK /usr/local/Cellar/glfw/3.3.6/lib/libglfw.3.dylib)
link_libraries(${OPENGL} ${GLEW_LINK} ${GLFW_LINK})
# 执行编译命令
set(SOURCE_FILES glad.c main.cpp)
add_executable(OpenGL ${SOURCE_FILES})
# mac下这步很重要
if (APPLE)
target_link_libraries(OpenGL "-framework OpenGL")
target_link_libraries(OpenGL "-framework GLUT")
endif()
cpp
#include <glad/glad.h>
#include <glfw3.h>
#include <iostream>
void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);
// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
const char *vertexShaderSource ="#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"layout (location = 1) in vec3 aColor;\n"
"out vec3 ourColor;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos, 1.0);\n"
" ourColor = aColor;\n"
"}\0";
const char *fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;\n"
"in vec3 ourColor;\n"
"void main()\n"
"{\n"
" FragColor = vec4(ourColor, 1.0f);\n"
"}\n\0";
int main()
{
// glfw: initialize and configure
// ------------------------------
glfwInit();//初始化glfw库
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);//设置openGL的主版本号
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);//设置openGL的次版本号
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);//profile设置openGL的配置文件
#ifdef __APPLE__
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif
// glfw window creation
// --------------------
GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);//创建一个窗口
if (window == NULL)
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
glfwMakeContextCurrent(window);//将当前上下文设置为窗口上下文
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);//设置窗口大小回调函数
// glad: load all OpenGL function pointers
// ---------------------------------------
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return -1;
}
// build and compile our shader program
// ------------------------------------
// vertex shader
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);//创建顶点着色器
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);//将顶点着色器附加到着色器对象上
glCompileShader(vertexShader);//编译顶点着色器
// check for shader compile errors
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);//检查顶点着色器是否编译成功
if (!success)
{
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// fragment shader
unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);//创建片段着色器
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);//添加对象
glCompileShader(fragmentShader);//编译片段着色器
// check for shader compile errors
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);//检查编译是否成功
if (!success)
{
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
}
// link shaders
unsigned int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// check for linking errors
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);//检查着色器链接是否错误
if (!success) {
glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
}
glDeleteShader(vertexShader);//删除顶点着色器
glDeleteShader(fragmentShader);//删除片段着色器
// set up vertex data (and buffer(s)) and configure vertex attributes
// ------------------------------------------------------------------
float vertices[] = {
// positions // colors
0.5f, -0.5f, 0.0f, 1.0f, 0.0f, 0.0f, // bottom right
-0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, // bottom left
0.0f, 0.5f, 0.0f, 0.0f, 0.0f, 1.0f // top
};
unsigned int VBO, VAO;
glGenVertexArrays(1, &VAO);//生成1个VAO
glGenBuffers(1, &VBO);//生成一个VBO
// bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);//绑定VBO
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);//将顶点数据传递到VBO
// position attribute 位置属性和颜色属性
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)0);//将当前顶点属性与VBO关联
glEnableVertexAttribArray(0);//启动顶点属性
// color attribute
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(3 * sizeof(float)));
glEnableVertexAttribArray(1);
// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other
// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.
// glBindVertexArray(0);
// as we only have a single shader, we could also just activate our shader once beforehand if we want to
glUseProgram(shaderProgram);//使用着色程序
// render loop 主任务渲染循环
// -----------
while (!glfwWindowShouldClose(window))
{
// input
// -----
processInput(window);//处理用户输入
// render
// ------
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);//清空颜色
glClear(GL_COLOR_BUFFER_BIT);//清空颜色缓冲区
// render the triangle
glBindVertexArray(VAO);//绑定VAO并绘制三角形
glDrawArrays(GL_TRIANGLES, 0, 3);//绘制三角形
// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
// -------------------------------------------------------------------------------
glfwSwapBuffers(window);//交换前后缓冲区
glfwPollEvents();//处理窗口事件
}
// optional: de-allocate all resources once they've outlived their purpose:
// ------------------------------------------------------------------------
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteProgram(shaderProgram);
// glfw: terminate, clearing all previously allocated GLFW resources.
// ------------------------------------------------------------------
glfwTerminate();//关闭glfw程序
return 0;
}
// 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);
}
// 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);
}
9.4.5 法线的计算
法线向量的计算通常需要根据具体的情况来决定,但是常见的方式包括以下几种:
(1)在顶点着色器中计算
法线向量乘以模型矩阵的逆转置矩阵来实现的
Normal = mat3(transpose(inverse(model))) * aNormal;
(2)在片段着色器中计算 (3)使用法线贴图
原文地址:https://blog.csdn.net/m0_47549429/article/details/136339934
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