OpenGL學習筆記(2) 畫一個正方形

畫一個正方形

其實，畫正方形就是畫兩個三角形，用四個頂點以及使用索引來實現
完整代碼在Square項目的Application.cpp里
先貼上窗口初始化代碼

void BaseInit()
{
	glfwInit();//初始化
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);//配置GLFW
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);//配置GLFW
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);//
	glfwWindowHint(GLFW_RESIZABLE, GL_TRUE);
	float screenWidth = 800.0f;
	float screenHeight = 600.0f;
	//創建窗口
	glWindow = glfwCreateWindow(screenWidth, screenHeight, "LearnOpenGL", nullptr, nullptr);
	if (glWindow == nullptr)
	{
		cout << "Failed to create GLFW window" << endl;
		glfwTerminate();
		return;
	}
	glfwMakeContextCurrent(glWindow);

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

畫一個普通的正方形

void NormalSquare()
{
	float vertices[] = {
		//     ---- 位置 ----
			 0.5f,  0.5f, 0.0f,  // 右上
			 0.5f, -0.5f, 0.0f,  // 右下
			-0.5f, -0.5f, 0.0f,  // 左下
			-0.5f,  0.5f, 0.0f,  // 左上
	};
	//索引
	unsigned int indices[] = {
		0,1,3,
		1,2,3
	};
	//編譯着色器
	Shader ourShader("vertex_1.vs", "fragment_1.fs");
	ourShader.use();//glUseProgram(shaderProgram);
	unsigned int VAO;
	//頂點數組
	glGenVertexArrays(1, &VAO);
	glBindVertexArray(VAO);
	//綁定頂點數組緩存
	unsigned int VBO;
	glGenBuffers(1, &VBO);
	glBindBuffer(GL_ARRAY_BUFFER, VBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	//綁定索引緩存
	unsigned int EBO;
	glGenBuffers(1, &EBO);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

	// 位置屬性
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
	glEnableVertexAttribArray(0);

	while (!glfwWindowShouldClose(glWindow))
	{
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);
		//draw
		glBindVertexArray(VAO);
		glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
		glBindVertexArray(0);
		glfwPollEvents();
		glfwSwapBuffers(glWindow);
	}
	glDeleteVertexArrays(1, &VAO);
	glDeleteBuffers(1, &VBO);
	glDeleteBuffers(1, &EBO);
	glfwTerminate();
}

最終效果

畫一個彩色的正方形

和上一個筆記里畫彩色三角形的邏輯一樣，在頂點屬性后面加上顏色屬性，設置數據訪問指針的屬性，記得頂點着色器要加上顏色的輸入(步長和相位)

//彩色正方形
void ColourfulSquare()
{
	float vertices[] = {
		//     ---- 位置 ----       ---- 顏色 ---- 
			 0.5f,  0.5f, 0.0f,   1.0f, 0.0f, 0.0f,  // 右上
			 0.5f, -0.5f, 0.0f,   0.0f, 1.0f, 0.0f,  // 右下
			-0.5f, -0.5f, 0.0f,   0.0f, 0.0f, 1.0f,  // 左下
			-0.5f,  0.5f, 0.0f,   1.0f, 1.0f, 0.0f,  // 左上
	};
	//索引
	unsigned int indices[] = {
		0,1,3,
		1,2,3
	};
	//編譯着色器
	Shader ourShader("vertex_4.vs", "fragment_4.fs");
	ourShader.use();//glUseProgram(shaderProgram);
	unsigned int VAO;
	//頂點數組
	glGenVertexArrays(1, &VAO);
	glBindVertexArray(VAO);
	//綁定頂點數組緩存
	unsigned int VBO;
	glGenBuffers(1, &VBO);
	glBindBuffer(GL_ARRAY_BUFFER, VBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
	
	//綁定索引緩存
	unsigned int EBO;
	glGenBuffers(1, &EBO);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

	// 位置屬性
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)0);
	glEnableVertexAttribArray(0);
	// 顏色屬性
	glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(3 * sizeof(float)));	//最后一個參數是數據的起點
	glEnableVertexAttribArray(1);

	while (!glfwWindowShouldClose(glWindow))
	{
		glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
		glClear(GL_COLOR_BUFFER_BIT);
		//draw
		glBindVertexArray(VAO);
		glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
		glBindVertexArray(0);
		glfwPollEvents();
		glfwSwapBuffers(glWindow);
	}
	glDeleteVertexArrays(1, &VAO);
	glDeleteBuffers(1, &VBO);
	glDeleteBuffers(1, &EBO);
	glfwTerminate();
}

最終效果

可以試試線框模式，在while之前加上
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
效果圖