[C++] [OpenGL] FreeGLUT+GLAD的简单示例

前言

最近突然打算写OpenGL1.0，于是打开GLFW，配置上下文，创建失败…
看来GLFW只支持现代OpenGL
于是我又转向FreeGLUT，打开示例，发现FreeGLUT原来是支持现代OpenGL的
OpenGL3.1官方示例
FreeGLUT
如何在Windows 10（64位）的MinGW-w64上设置OpenGL

FreeGLUT函数说明

1.glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);'设置显示模式，这里是双缓冲（GLUT_DOUBLE），所以需要调用glutSwapBuffers();
2.glutInitContextVersion(3, 3);设置上下文版本，这里是OpenGL3.3
3.glutInitContextFlags(GLUT_FORWARD_COMPATIBLE | GLUT_DEBUG);设置上下文标志（？？？），向前兼容（GLUT_FORWARD_COMPATIBLE）
4.glutInitContextProfile(GLUT_CORE_PROFILE);设置为核心模式（？？？）

代码

#include "glad.c"
#include <GL/freeglut.h>
#include <iostream>

const char* vSource = "#version 330 core\nlayout(location=0)in vec3 a_position;\nlayout(location=1)in vec3 a_color;\nout vec3 v_color;\nvoid main(){gl_Position = vec4(a_position,1.0);\nv_color = a_color;}";
const char* fSource = "#version 330 core\nin vec3 v_color;\nout vec4 o_color;\nvoid main(){o_color = vec4(v_color,1.0);}";
GLfloat ver[] =
{
	0.0, 0.5, 0.0,
	-0.5, -0.5, 0.0,
	0.5, -0.5, 0.0
};
GLfloat col[] =
{
	1.0, 0.0, 0.0,
	0.0, 1.0, 0.0,
	0.0, 0.0, 1.0
};

GLuint program;
GLuint vao;

void display();
void keyboard(unsigned char key, int x, int y);
bool init();
bool loadProgram();
bool loadVAO();
void debug(char* title);

int main(int argc, char* argv[])
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
	glutInitContextVersion(3, 3);
	glutInitContextFlags(GLUT_FORWARD_COMPATIBLE | GLUT_DEBUG);
	glutInitContextProfile(GLUT_CORE_PROFILE);
	glutInitWindowPosition(0, 0);
	glutInitWindowSize(500, 500);
	glutCreateWindow("GLUT - OpenGL 3.3");

	glutDisplayFunc(display);
	glutKeyboardFunc(keyboard);

	if (!init())
	{
		std::cout << "Failed to initialize." << std::endl;
		return -1;
	}

	glutMainLoop();

	return 0;
}

void display()
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glUseProgram(program);
	glBindVertexArray(vao);
	glDrawArrays(GL_TRIANGLES, 0, 3);
	glBindVertexArray(0);

	glutSwapBuffers();
}

void keyboard(unsigned char key, int x, int y)
{
	switch (key)
	{
		case 27:
			exit(0);
			break;
	}
}

bool init()
{
	if (!gladLoadGL())
	{
		std::cout << "Failed to init GL." << std::endl;
		return false;
	}

	if (!loadProgram())
	{
		std::cout << "Failed to init program." << std::endl;
		return false;
	}

	if (!loadVAO())
	{
		std::cout << "Failed to init VAO." << std::endl;
		return false;
	}

	return true;
}

bool loadProgram()
{
	GLuint vs = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vs, 1, &vSource, nullptr);
	glCompileShader(vs);

	GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fs, 1, &fSource, nullptr);
	glCompileShader(fs);

	program = glCreateProgram();
	glAttachShader(program, vs);
	glAttachShader(program, fs);
	glLinkProgram(program);

	int success;
	glGetProgramiv(program, GL_LINK_STATUS, &success);
	if (success == false)
	{
		std::cout << "Failed to link program." << std::endl;
		return false;
	}

	debug("loadProgram");

	return true;
}

bool loadVAO()
{
	GLuint vbo1, vbo2;
	glGenBuffers(1, &vbo1);
	glGenBuffers(1, &vbo2);

	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);

	glBindBuffer(GL_ARRAY_BUFFER, vbo1);
	glBufferData(GL_ARRAY_BUFFER, sizeof(ver), ver, GL_STATIC_DRAW);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), nullptr);

	glBindBuffer(GL_ARRAY_BUFFER, vbo2);
	glBufferData(GL_ARRAY_BUFFER, sizeof(col), col, GL_STATIC_DRAW);
	glEnableVertexAttribArray(1);
	glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), nullptr);

	glBindVertexArray(0);

	glDeleteBuffers(1, &vbo1);
	glDeleteBuffers(1, &vbo2);

	debug("loadVAO");

	return true;
}

void debug(char* title)
{
	GLenum error = glGetError();
	if (error != GL_NO_ERROR)
	{
		std::cout << title << ":" << error << std::endl;

	}
}

运行参数

我是用MinGW编译的，所以要加上参数

运行结果