GLM简单使用

glm是一个开源的对矩阵运算的库，下载地址：
https://github.com/g-truc/glm/releases
直接包含其头文件即可使用：

#include <glad/glad.h>//glad必须在glfw头文件之前包含
#include <GLFW/glfw3.h>
#include <iostream>
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

//GLM
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#define GLM_ENABLE_EXPERIMENTAL
#include <glm/gtx/string_cast.hpp>

void frameBufferSizeCallbakc(GLFWwindow* window, int width, int height)
{
	glViewport(0, 0, width, height);
}
void glfwKeyCallback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
}

GLuint program = 0;
GLuint vao = 0;
GLuint texture = 0;
glm::mat4 transform(1.0f);//4×4单位矩阵
//旋转
void doRotationTransform()
{
	//构建一个旋转矩阵，绕着z轴旋转45度角
	//rotate函数：用于生成旋转矩阵
	//bug1:rotate必须得到一个float类型的角度，c++的template
	//bug2:rotate函数接受的不是角度（degree），接收的弧度（radians）
	//注意点：radians函数也是模板函数，切记要传入float类型数据，加f后缀
	transform = glm::rotate(glm::mat4(1.0), glm::radians(90.f), glm::vec3(0.0, 0.0, 1.0));
}
//平移
void doTranslationTransform()
{
	transform = glm::translate(glm::mat4(1.0), glm::vec3(0.5f, 0.0, 0.0));
}
//缩放
void doScaleTransform()
{
	//x缩放0.1，y缩放0.5，z不缩放
	transform = glm::scale(glm::mat4(1.0), glm::vec3(0.1f, 0.5f, 1.0f));
}
//复合变换
void doTransform()
{
	glm::mat4 rotateMat = glm::rotate(glm::mat4(1.0f), glm::radians(90.0f), glm::vec3(0.0, 0.0, 1.0));
	glm::mat4 translateMat = glm::translate(glm::mat4(1.0f), glm::vec3(0.5f, 0.0f, 0.0f));
	//先旋转 再平移
	transform = translateMat * rotateMat;
	//先平移 后旋转
	//transform = rotateMat * translateMat;
}
float angle = 0.0f;
void doRotation()
{
	angle += 2.0f;
	//每一帧都会“重新”构建一个旋转矩阵
	transform = glm::rotate(glm::mat4(1.0f), glm::radians(angle), glm::vec3(0.0f, 0.0f, 1.0f));;
}
void prepareVAO()
{
	//positions
	float positions[] = {
		-0.5f, -0.5f, 0.0f,
		0.5f, -0.5f, 0.0f,
		0.0f,  0.5f, 0.0f,
	};
	//颜色
	float colors[] = {
		1.0f, 0.0f,0.0f,
		0.0f, 1.0f,0.0f,
		0.0f, 0.0f,1.0f
	};
	//索引
	unsigned int indices[] = {
		0, 1, 2,
	};
	//uv坐标
	float uvs[] = {
		0.0f, 0.0f,
		1.0f, 0.0f,
		0.5f, 1.0f,
	};

	//2 VBO创建
	GLuint posVbo = 0;
	GLuint colorVbo = 0;
	GLuint uvVbo = 0;
	glGenBuffers(1, &posVbo);
	glBindBuffer(GL_ARRAY_BUFFER, posVbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);

	glGenBuffers(1, &colorVbo);
	glBindBuffer(GL_ARRAY_BUFFER, colorVbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(colors), colors, GL_STATIC_DRAW);

	glGenBuffers(1, &uvVbo);
	glBindBuffer(GL_ARRAY_BUFFER, uvVbo);
	glBufferData(GL_ARRAY_BUFFER, sizeof(uvs), uvs, GL_STATIC_DRAW);

	//3 EBO创建
	GLuint ebo = 0;
	glGenBuffers(1, &ebo);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

	//4 VAO创建
	vao = 0;
	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);

	//5 绑定vbo ebo 加入属性描述信息
	//5.1 加入位置属性描述信息
	glBindBuffer(GL_ARRAY_BUFFER, posVbo);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);

	//5.2 加入颜色属性描述信息
	glBindBuffer(GL_ARRAY_BUFFER, colorVbo);
	glEnableVertexAttribArray(1);
	glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);

	//5.3 加入uv属性描述数据
	glBindBuffer(GL_ARRAY_BUFFER, uvVbo);
	glEnableVertexAttribArray(2);
	glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), (void*)0);

	//5.2 加入ebo到当前的vao
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);

	glBindVertexArray(0);
}
void prepareShader() {
	//1 完成vs与fs的源代码，并且装入字符串
	const char* vertexShaderSource =
		"#version 330 core\n"
		"layout (location = 0) in vec3 aPos;\n"
		"layout (location = 1) in vec3 aColor;\n"
		"layout (location = 2) in vec2 aUV;\n"
		"out vec3 color;\n"
		"out vec2 uv;\n"
		"uniform mat4 transform;\n"
		"void main()\n"
		"{\n"
		"   vec4 position = vec4(aPos, 1.0);\n"
		"   position = transform * position;\n"
		"   gl_Position = position;\n"
		"   color = aColor;\n"
		"   uv = aUV;\n"
		"}\0";
	const char* fragmentShaderSource =
		"#version 330 core\n"
		"out vec4 FragColor;\n"
		"in vec3 color;\n"
		"in vec2 uv;\n"
		"uniform sampler2D sampler;\n"
		"void main()\n"
		"{\n"
		"   FragColor = texture(sampler, uv);\n"
		"}\n\0";


	//2 创建Shader程序（vs、fs）
	GLuint vertex, fragment;
	vertex = glCreateShader(GL_VERTEX_SHADER);
	fragment = glCreateShader(GL_FRAGMENT_SHADER);


	//3 为shader程序输入shader代码
	glShaderSource(vertex, 1, &vertexShaderSource, NULL);
	glShaderSource(fragment, 1, &fragmentShaderSource, NULL);

	int success = 0;
	char infoLog[1024];
	//4 执行shader代码编译 
	glCompileShader(vertex);
	//检查vertex编译结果
	glGetShaderiv(vertex, GL_COMPILE_STATUS, &success);
	if (!success) {
		glGetShaderInfoLog(vertex, 1024, NULL, infoLog);
		std::cout << "Error: SHADER COMPILE ERROR --VERTEX" << "\n" << infoLog << std::endl;
	}

	glCompileShader(fragment);
	//检查fragment编译结果
	glGetShaderiv(fragment, GL_COMPILE_STATUS, &success);
	if (!success) {
		glGetShaderInfoLog(fragment, 1024, NULL, infoLog);
		std::cout << "Error: SHADER COMPILE ERROR --FRAGMENT" << "\n" << infoLog << std::endl;
	}

	//5 创建一个Program壳子
	program = glCreateProgram();

	//6 将vs与fs编译好的结果放到program这个壳子里
	glAttachShader(program, vertex);
	glAttachShader(program, fragment);

	//7 执行program的链接操作，形成最终可执行shader程序
	glLinkProgram(program);

	//检查链接错误
	glGetProgramiv(program, GL_LINK_STATUS, &success);
	if (!success) {
		glGetProgramInfoLog(program, 1024, NULL, infoLog);
		std::cout << "Error: SHADER LINK ERROR " << "\n" << infoLog << std::endl;
	}

	//清理
	glDeleteShader(vertex);
	glDeleteShader(fragment);
}

void prepareTextrue()
{
	//1 stbImage 读取图片
	int width, height, channels;
	//--反转y轴
	stbi_set_flip_vertically_on_load(true);
	unsigned char* data = stbi_load("goku.jpg", &width, &height, &channels, STBI_rgb_alpha);

	//2 生成纹理并且激活单元绑定
	glGenTextures(1, &texture);
	//--激活纹理单元--
	glActiveTexture(GL_TEXTURE0);
	//--绑定纹理对象--
	glBindTexture(GL_TEXTURE_2D, texture);

	//3 传输纹理数据,开辟显存
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);

	//***释放数据
	stbi_image_free(data);

	//4 设置纹理的过滤方式
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

	//5 设置纹理的包裹方式
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);//u
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);//v
}

void render()
{
	//执行opengl画布清理操作
	glClear(GL_COLOR_BUFFER_BIT);

	//1.绑定当前的program
	glUseProgram(program);

	//2 更新Uniform的时候，一定要先UserProgram
	//2.1 通过名称拿到Uniform变量的位置Location
	GLint location = glGetUniformLocation(program, "sampler");
	//2.2 通过Location更新Uniform变量的值
	glUniform1f(location, 0);

	GLint locationTransform = glGetUniformLocation(program, "transform");
	//transpose参数：表示是否对传输进去的矩阵数据进行转置
	glUniformMatrix4fv(locationTransform, 1, GL_FALSE, glm::value_ptr(transform));

	//3 绑定当前的vao
	glBindVertexArray(vao);
	//4 发出绘制指令
	//glDrawArrays(GL_TRIANGLE_STRIP, 0, 6);
	glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0);
}


int main()
{
	//初始化glfw环境
	glfwInit();
	//设置opengl主版本号
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	//设置opengl次版本号
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	//设置opengl启用核心模式
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	//创建窗体对象
	GLFWwindow* window = glfwCreateWindow(800, 600, "lenarnOpenGL", nullptr, nullptr);
	//设置当前窗体对象为opengl的绘制舞台
	glfwMakeContextCurrent(window);
	//窗体大小回调
	glfwSetFramebufferSizeCallback(window, frameBufferSizeCallbakc);
	//键盘相应回调
	glfwSetKeyCallback(window, glfwKeyCallback);

	//使用glad加载所有当前版本opengl的函数
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		std::cout << "初始化glad失败" << std::endl;
		return -1;
	}
	;
	//设置opengl视口大小和清理颜色
	glViewport(0, 0, 800, 600);
	glClearColor(0.2f, 0.3f, 0.3f, 1.0f);

	//shader
	prepareShader();
	//vao
	prepareVAO();
	//texture
	prepareTextrue();
	//doTransform();
	//执行窗体循环
	while (!glfwWindowShouldClose(window))
	{
		//接受并分发窗体消息
		//检查消息队列是否有需要处理的鼠标、键盘等消息
		//如果有的话就将消息批量处理，清空队列
		glfwPollEvents();
		doRotation();
		//渲染操作
		render();
		//切换双缓存
		glfwSwapBuffers(window);
	}

	//推出程序前做相关清理
	glfwTerminate();
	return 0;
}

上述代码分别实现了对图像进行旋转平移缩放的操作。
在VS中定义transform四维矩阵变量，将这个变量与位置向量进行相乘即可进行旋转平移缩放。

叠加变换

上面的旋转三角形可以通过叠加来实现

void doTransform()
{
	旋转三角形
	float angle = 1.0f;
	transform = glm::rotate(transform, glm::radians(angle), glm::vec3(0.0f, 0.0f, 1.0f));
}

在每一帧进行渲染时调用此函数即可