OpenGL uniform的用法

Uniform是一种从CPU中的应用向GPU中的着色器发送数据的方式，但uniform和顶点属性有些不同。首先，uniform是全局的(Global)。全局意味着uniform变量必须在每个着色器程序对象中都是独一无二的，而且它可以被着色器程序的任意着色器在任意阶段访问。第二，无论你把uniform值设置成什么，uniform会一直保存它们的数据，直到它们被重置或更新。

使用Uniform修改颜色

#include <glad/glad.h>
#include <GLFW/glfw3.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

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"
"void main()\n"
"{\n"
"   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
const char *fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;"
"uniform vec4 ourColor;\n"
"void main()\n"
"{\n"
"   FragColor = ourColor;\n"
"}\n\0";
const char *fragmentShaderSource2 = "#version 330 core\n"
"out vec4 FragColor;\n"
"void main()\n"
"{\n"
"   FragColor = vec4(0.98f, 0.625f, 0.12f, 1.0f);\n"
"}\n\0";

int main()
{
	// 初始化配置

	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "windown", NULL, NULL);
	if (window == NULL)
	{
		std::cout << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);//设置上下文
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}


	// 创建着色器 Progroam
	// ------------------------------------
	//  顶点着色器
	int vertexShader = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
	glCompileShader(vertexShader);
	int success;
	char infoLog[512];
	glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
	if (!success)
	{
		glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	// 第一个片元着色器
	int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
	glCompileShader(fragmentShader);

	glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
	if (!success)
	{
		glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	//第二个片元着色器
	int fragmentShader2 = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader2, 1, &fragmentShaderSource2, NULL);
	glCompileShader(fragmentShader2);

	glGetShaderiv(fragmentShader2, GL_COMPILE_STATUS, &success);
	if (!success)
	{
		glGetShaderInfoLog(fragmentShader2, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	// 创建第一个着色器程序
	int shaderProgram = glCreateProgram();
	glAttachShader(shaderProgram, vertexShader);
	glAttachShader(shaderProgram, fragmentShader);
	glLinkProgram(shaderProgram);
	// 检查连接
	glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
	if (!success) {
		glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
	}
	// 创建第二个着色器程序
	int shaderProgram2 = glCreateProgram();
	glAttachShader(shaderProgram2, vertexShader);
	glAttachShader(shaderProgram2, fragmentShader2);
	glLinkProgram(shaderProgram2);
	// 检查连接
	glGetProgramiv(shaderProgram2, GL_LINK_STATUS, &success);
	if (!success) {
		glGetProgramInfoLog(shaderProgram2, 512, NULL, infoLog);
		std::cout << "ERROR::SHADER::PROGRAM::LINKING_FAILED\n" << infoLog << std::endl;
	}
	glDeleteShader(vertexShader);
	glDeleteShader(fragmentShader);
	glDeleteShader(fragmentShader2);
	float firstTriangle[] = 
	{
		//第一个三角形
		-0.9f, -0.5f, 0.0f,  // 左
		-0.0f, -0.5f, 0.0f,  // 右
		-0.45f, 0.5f, 0.0f,  // 上 
	};
	float secondTriangle[] = 
	{
		// 第二个三角形
		 0.0f, -0.5f, 0.0f,  // 左
		 0.9f, -0.5f, 0.0f,  // 右
		 0.45f, 0.5f, 0.0f   // 上 
	};

	unsigned int VBOs[2], VAOs[2];
	glGenVertexArrays(2, VAOs);//生成VAO对象
	glGenBuffers(2, VBOs);//生成VBO对象

	glBindVertexArray(VAOs[0]);//绑定VAO对象
	glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(firstTriangle), firstTriangle, GL_STATIC_DRAW);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);//设置顶点属性指针
	glEnableVertexAttribArray(0);
	//把用户定义的数据复制到当前绑定缓冲的函数。
	//它的第一个参数是目标缓冲的类型：顶点缓冲对象当前绑定到GL_ARRAY_BUFFER目标上。
	//第二个参数指定传输数据的大小(以字节为单位)；用一个简单的sizeof计算出顶点数据大小就行。
	//第三个参数是我们希望发送的实际数据。

	glBindVertexArray(VAOs[1]);//绑定VAO对象
	glBindBuffer(GL_ARRAY_BUFFER, VBOs[1]);
	glBufferData(GL_ARRAY_BUFFER, sizeof(secondTriangle), secondTriangle, GL_STATIC_DRAW);

	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
	glEnableVertexAttribArray(0);


	glBindBuffer(GL_ARRAY_BUFFER, 0);

	glBindVertexArray(0);



	while (!glfwWindowShouldClose(window))
	{

		processInput(window);
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);

		glUseProgram(shaderProgram);
		float timeValue = glfwGetTime();
		float greenValue = sin(timeValue) / 2.0f + 0.5f;
		int vertexColorLocation = glGetUniformLocation(shaderProgram, "ourColor");
		glUniform4f(vertexColorLocation, 0.0f, greenValue, 0.0f, 1.0f);
		glBindVertexArray(VAOs[0]);
		glDrawArrays(GL_TRIANGLES, 0, 3);
		glUseProgram(shaderProgram2);
		glBindVertexArray(VAOs[1]);
		glDrawArrays(GL_TRIANGLES, 0, 3);
		glfwSwapBuffers(window);
		glfwPollEvents();
	}


	glDeleteVertexArrays(2, VAOs);
	glDeleteBuffers(2, VBOs);


	glfwTerminate();
	return 0;
}


void processInput(GLFWwindow *window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
		glfwSetWindowShouldClose(window, true);
}


void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
	glViewport(0, 0, width, height);
}