OpenGL之——画不同颜色的三角形（uniform简便方法）

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这里有两种渲染方法：

(一)  一种是建立两套着色器，两个着色器程序，分别渲染两种颜色；

(二)  另一种是简单方法，通过定义在片段着色器中的uniform标志值可以随意切换不同的颜色，用不同的颜色状态来同时渲染不同的图形。

先看笨方法也就是第一种，代码如下：

#include <iostream>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#pragma comment(lib,"glfw3.lib")

using namespace std;

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

const char *vertexShaderSource =
"#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main(){\n"
"gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0f);\n"
"}\n\0";

const char *fragmentShaderSource_1 =
"#version 330 core\n"
"out vec4 FragColor;\n"
"uniform int flag = 1;\n"
"void main(){\n"
"	FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\n\0";

const char *fragmentShaderSource_2 =
"#version 330 core\n"
"out vec4 FragColor;\n"
"void main(){\n"
"FragColor = vec4(1.0f, 1.0f, 0.0f, 1.0f);\n"
"}\n\0";



int main() {
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	

	GLFWwindow* window = glfwCreateWindow(800, 600, "LearnOpenGL", NULL, NULL);
	if (window == NULL) {
		cout << "Failed to create GLFW window" << endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){
		cout << "Failed to initialize GLAD" << endl;
		return -1;
	}
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

	
	//创建顶点缓存对象用来管理分配到的顶点缓存空间
	//创建一个着色器对象
	GLuint 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);
		cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	//创建一个片段着色器
	GLuint fragmentShader1 = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader1, 1, &fragmentShaderSource_1, NULL);
	glCompileShader(fragmentShader1);
	glGetShaderiv(fragmentShader1, GL_COMPILE_STATUS, &success);
	if (!success) {
		glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
		cout << "ERROR::SHADER::FRAGMENT1::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	GLuint fragmentShader2 = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader2, 1, &fragmentShaderSource_2, NULL);
	glCompileShader(fragmentShader2);
	glGetShaderiv(fragmentShader2, GL_COMPILE_STATUS, &success);
	if (!success) {
		glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
		cout << "ERROR::SHADER::FRAGMENT2::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	//创建着色器程序
	GLuint shaderProgram1 = glCreateProgram();
	GLuint shaderProgram2 = glCreateProgram();
	//链接着色器
	glAttachShader(shaderProgram1, vertexShader);
	glAttachShader(shaderProgram1, fragmentShader1);
	glLinkProgram(shaderProgram1);
	glGetProgramiv(shaderProgram1, GL_LINK_STATUS, &success);
	if (!success) {
		glGetProgramInfoLog(shaderProgram1, 512, NULL, infoLog);
		cout << "ERROR::SHADER::PROGRAM1::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	glAttachShader(shaderProgram2, vertexShader);
	glAttachShader(shaderProgram2, fragmentShader2);
	glLinkProgram(shaderProgram2);
	glGetProgramiv(shaderProgram2, GL_LINK_STATUS, &success);
	if (!success) {
		glGetProgramInfoLog(shaderProgram2, 512, NULL, infoLog);
		cout << "ERROR::SHADER::PROGRAM2::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	glDeleteShader(vertexShader);
	glDeleteShader(fragmentShader1);
	glDeleteShader(fragmentShader2);
	GLfloat vertices1[] = {
		// 第一个三角形
		0.5f, 0.5f, 0.0f,   // 右上角
		0.5f, -0.5f, 0.0f,  // 右下角
		-0.5f, 0.5f, 0.0f,  // 左上角
	}; 
	GLfloat vertices2[] = {
		// 第二个三角形
		0.5f, -0.5f, 0.0f,  // 右下角
		-0.5f, -0.5f, 0.0f, // 左下角
		-0.5f, 0.5f, 0.0f   // 左上角
	};
	GLuint VAO[2], VBO[2];
	glGenVertexArrays(2, VAO);//创建顶点数组对象
	glGenBuffers(2, VBO);//创建顶点缓冲对象


	//复制顶点数组到缓冲中供OpenGL使用
	glBindVertexArray(VAO[0]);//将顶点数组绑定到顶点数组对象
	glBindBuffer(GL_ARRAY_BUFFER, VBO[0]);//将顶点缓冲绑定到顶点缓冲对象
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices1), vertices1, GL_STATIC_DRAW);//缓冲区三角形顶点数据
	//设置顶点属性指针
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
	glEnableVertexAttribArray(0);

	//复制顶点数组到缓冲中供OpenGL使用
	glBindVertexArray(VAO[1]);//将顶点数组绑定到顶点数组对象
	glBindBuffer(GL_ARRAY_BUFFER, VBO[1]);//将顶点缓冲绑定到顶点缓冲对象
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices2), vertices2, GL_STATIC_DRAW);//缓冲区三角形顶点数据
	//设置顶点属性指针
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
	glEnableVertexAttribArray(0);

	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindVertexArray(0);

	

	
	//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
	while (!glfwWindowShouldClose(window)) {
		processInput(window);

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

		glUseProgram(shaderProgram1);
		glBindVertexArray(VAO[0]);
		glDrawArrays(GL_TRIANGLES, 0, 3);
		glBindVertexArray(0);
		//glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0);

		glUseProgram(shaderProgram2);
		glBindVertexArray(VAO[1]);
		glDrawArrays(GL_TRIANGLES, 0, 3);
		glBindVertexArray(0);
		//glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, (const void*)3);
		glfwSwapBuffers(window);
		glfwPollEvents();
	}
	glDeleteBuffers(2, VBO);
	glDeleteVertexArrays(2, VAO);
	glfwTerminate();
	return 0;
}

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

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

第二种方法，新探索的极简方法：

#include <iostream>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#pragma comment(lib,"glfw3.lib")

using namespace std;

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

const char *vertexShaderSource =
"#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main(){\n"
"gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0f);\n"
"}\n\0";

const char *fragmentShaderSource =
"#version 330 core\n"
"out vec4 FragColor;\n"
"uniform int flag = 1;\n"
"void main(){\n"
"if(flag == 1)\n"
"	FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"else if(flag == 2)\n"
"	FragColor = vec4(1.0f, 1.0f, 0.0f, 1.0f);\n"
"}\n\0";



int main() {
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	

	GLFWwindow* window = glfwCreateWindow(800, 600, "LearnOpenGL", NULL, NULL);
	if (window == NULL) {
		cout << "Failed to create GLFW window" << endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)){
		cout << "Failed to initialize GLAD" << endl;
		return -1;
	}
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

	
	//创建顶点缓存对象用来管理分配到的顶点缓存空间
	//创建一个着色器对象
	GLuint 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);
		cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	//创建一个片段着色器
	GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
	glCompileShader(fragmentShader);
	glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
	if (!success) {
		glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
		cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	
	//创建着色器程序
	GLuint shaderProgram = glCreateProgram();
	//链接着色器
	glAttachShader(shaderProgram, vertexShader);
	glAttachShader(shaderProgram, fragmentShader);
	glLinkProgram(shaderProgram);
	glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
	if (!success) {
		glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
		cout << "ERROR::SHADER::PROGRAM::COMPILATION_FAILED\n" << infoLog << std::endl;
	}
	
	glDeleteShader(vertexShader);
	glDeleteShader(fragmentShader);
	GLfloat vertices[] = {
		// 第一个三角形
		0.5f, 0.5f, 0.0f,   // 右上角
		0.5f, -0.5f, 0.0f,  // 右下角
		-0.5f, 0.5f, 0.0f,  // 左上角
		// 第二个三角形
		0.5f, -0.5f, 0.0f,  // 右下角
		-0.5f, -0.5f, 0.0f, // 左下角
		-0.5f, 0.5f, 0.0f   // 左上角
	}; 
	
	GLuint VAO, VBO;
	glGenVertexArrays(1, &VAO);//创建顶点数组对象
	glGenBuffers(1, &VBO);//创建顶点缓冲对象


	//复制顶点数组到缓冲中供OpenGL使用
	glBindVertexArray(VAO);//将顶点数组绑定到顶点数组对象
	glBindBuffer(GL_ARRAY_BUFFER, VBO);//将顶点缓冲绑定到顶点缓冲对象
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);//缓冲区三角形顶点数据
	//设置顶点属性指针
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
	glEnableVertexAttribArray(0);


	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindVertexArray(0);

	

	
	//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
	while (!glfwWindowShouldClose(window)) {
		processInput(window);

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

		glUseProgram(shaderProgram);
		int flagLoc = glGetUniformLocation(shaderProgram, "flag");
		glUniform1i(flagLoc, 2);
		glBindVertexArray(VAO);
		glDrawArrays(GL_TRIANGLES, 0, 3);

		glUniform1i(flagLoc, 1);
		glDrawArrays(GL_TRIANGLES, 3, 3);
		glBindVertexArray(0);
		glfwSwapBuffers(window);
		glfwPollEvents();
	}
	glDeleteBuffers(1, &VBO);
	glDeleteVertexArrays(1, &VAO);
	glfwTerminate();
	return 0;
}

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

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

perfect ：