实现3D引擎（五）- 绘制五边形

淡淡的烟草味﹌ 2022-03-27 08:09 237阅读 0赞

本文绘制一个颜色随时间变化的五边形。

在片元着色器中设置uniform变量。uniform变量可以接收CPU中发送到着色器的数据，用以设置图形的颜色。片元着色器的定义如下：

#version 330 core
    uniform vec4 vertexColor; 
    out vec4 color;
    void main()
    {
        color = vertexColor;
    }

设置随着时间改变的颜色，代码如下：

float timeValue = glfwGetTime();
    float greenValue = (sin(timeValue) / 2.0f) + 0.5f;
    int vertexColorLocation = glGetUniformLocation(shaderProgram, "vertexColor");
    //启用着色器程序
    glUseProgram(shaderProgram);
    glUniform4f(vertexColorLocation, 0, greenValue, 0, 1.0f);

首先，通过glfwGetTime()获取运行的秒数，使用sin函数让颜色在0.0到1.0之间改变，将结果储存到greenValue里。

然后，用glGetUniformLocation查询uniform `vertexColor`的位置值。

最后，通过glUniform4f函数设置uniform值。

程序完整的代码如下：

#include<iostream>
    #define GLEW_STATIC
    #include<GL/glew.h>
    #include<GLFW/glfw3.h>
    
    const char* vertexShaderSource =
    "#version 330 core                     \n"
    "layout(location = 0) in vec3 position; \n"
    "void main() {                          \n"
    "		gl_Position = vec4(position.x, position.y, position.z, 1.0);  \n"
    "} \n ";
    
    const char* fragmentShaderSource =
    "#version 330 core                   \n"
    "uniform vec4 vertexColor;                \n"
    "out vec4 color;                     \n"
    "void main(){                        \n"
    "	color = vertexColor;             \n"
    "}  \n";
    
    GLfloat vertices[] = {
    	-0.5f, -0.5f, 0.0f,   //0
    	0.5f, -0.5f, 0.0f,	  //1
    	0.0f,  0.5f, 0.0f,	  //2	  
    	0.7f, 0.0f, 0.0f,	  //3
    	0.8f, 0.8f, 0.0f	  //4
    };
    
    unsigned int indices[] = {
    	0,1,2,
    	2,1,3,
    	2,3,4
    };
    
    //key表示按下的键，action表示键按下/释放，mode表示是否有Ctrl、Shift、Alt等按钮操作
    void key_callback(GLFWwindow * window, int key, int scancode, int action, int mode)
    {
    	//用户按下ESC键，设置窗口WindowShouldClose属性为true,关闭应用程序
    	if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
    		glfwSetWindowShouldClose(window, GL_TRUE);
    }
    
    int main()
    {
    	glfwInit();
    	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);    //主版本号
    	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);    //次版本号
    	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);//核心模式
    	
    	GLFWwindow* window = glfwCreateWindow(800,600,"OpenGL Game",NULL,NULL); //创建窗口
    	if (window == NULL)
    	{
    		std::cout << "Open window failed!" << std::endl;
    		glfwTerminate();
    		return -1;
    	}
    	//将窗口的上下文设置为当前线程的主上下文
    	glfwMakeContextCurrent(window);
    	
    	//GLEW是用来管理OpenGL的函数指针,调用任何OpenGL的函数之前都需要初始化GLEW
    	glewExperimental = GL_TRUE;
    	if (glewInit() != GLEW_OK)
    	{
    		std::cout << "Init Glew failed！" << std::endl;
    		glfwTerminate();
    		return -1;
    	}
    
    	int width, height;
    	//从GLFW中获取视口大小
    	glfwGetFramebufferSize(window,&width,&height);
    	//窗口左下角的位置、宽度、高度
    	glViewport(0,0, width, height);
    	//glEnable(GL_CULL_FACE);
    	//glCullFace(GL_BACK);
    	//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    	//注册按键回调函数
    	glfwSetKeyCallback(window, key_callback);
    
    	//顶点数组对象
    	unsigned int VAO;
    	glGenVertexArrays(1,&VAO);
    	glBindVertexArray(VAO);
    
    	//顶点缓冲对象
    	unsigned int VBO;
    	glGenBuffers(1, &VBO);
    	glBindBuffer(GL_ARRAY_BUFFER,VBO);
    	//将顶点数据复制到缓冲中
    	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    	
    	//索引缓冲对象
    	unsigned int EBO;
    	glGenBuffers(1,&EBO);
    	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
    
    	//创建顶点着色器
    	unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
    	glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    	glCompileShader(vertexShader);
    
    	//创建片段着色器
    	unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    	glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
    	glCompileShader(fragmentShader);
    
    	//创建着色器程序
    	unsigned int shaderProgram = glCreateProgram();
    	glAttachShader(shaderProgram, vertexShader);
    	glAttachShader(shaderProgram, fragmentShader);
    	glLinkProgram(shaderProgram);
    	
    	//顶点属性配置,告诉OpenGL该如何解析顶点数据
    	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), (void*)0);
    	glEnableVertexAttribArray(0);
    
    	//检查GLFW是否要求退出
    	while (!glfwWindowShouldClose(window))
    	{
    		//检查是否触发事件（鼠标移动、键盘输入等），如果有则调用相应的回调函数
    		glfwPollEvents();
    		//渲染操作放入循环中
    		//清屏
    		glClearColor(0.2f, 0.3f, 0.3f, 1.0);
    		glClear(GL_COLOR_BUFFER_BIT);
    
    		glBindVertexArray(VAO);
    		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    
    		float timeValue = glfwGetTime();
    		float greenValue = (sin(timeValue) / 2.0f) + 0.5f;
    		int vertexColorLocation = glGetUniformLocation(shaderProgram, "vertexColor");
    		//启用着色器程序
    		glUseProgram(shaderProgram);
    		glUniform4f(vertexColorLocation, 0, greenValue, 0, 1.0f);
    
    		//绘制
    		glDrawElements(GL_TRIANGLES, 9,GL_UNSIGNED_INT,0);
    		//glDrawArrays(GL_TRIANGLES, 0, 6);
    		//交换颜色缓冲
    		glfwSwapBuffers(window);
    	}
    	//结束时释放资源
    	glfwTerminate();
    	return 0;
    }

输出结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70]: /images/20220327/0d55e6cd4ad74f329666d0ea247df778.png