OpenGL学习之绘制三角形

时间：2022-03-29 04:03:56

开发环境：

MAC、xcode

上代码:

1.main.cpp

//
// main.cpp
// GL_example
//
// Created by LiYong on 2018/2/28.
//

#include <iostream>
#include "Argument.h"
#include "Function.h"
using namespace std;
int main()
{
    initGL();

    GLFWwindow *window = glfwCreateWindow(800, 600, "LEARN OPENGL!", nullptr, nullptr);
    if (window == nullptr)
    {
        cout << "Failed to create GLFW window" << endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetKeyCallback(window, key_callback);

    glewExperimental = GL_TRUE;
    if (glewInit() != GLEW_OK)
    {
        std::cout << "Failed to initialize GLEW" << std::endl;
        return -1;
    }

    int width,height;
    glfwGetFramebufferSize(window, &width, &height);
    glViewport(0, 0, width, height);

    initShader();
    //1.绘制一个三角形
// renderTriangle();
    //2.绘制两个三角形组成一个矩形
// ElementBufferTest();
    //3.绘制两个三角形
// drawTwoTriangles();
    //4.使用不同的VAO、VBO绘制两个三角形
    drawTwoSameTriangles();

    while (!glfwWindowShouldClose(window))
    {
        glfwPollEvents();
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shaderProgram);
// glBindVertexArray(VAO);
// glDrawArrays(GL_TRIANGLES, 0, 6);
// glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);//以填充模式绘制（默认）
        glBindVertexArray(VAOs[0]);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);//以线框模式绘制
        glUseProgram(shaderProgramYellow);
        glBindVertexArray(VAOs[1]);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glBindVertexArray(0);


        glfwSwapBuffers(window);
    }

    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteBuffers(1, &EBO);
    glfwTerminate();
    return 0;
}
void initGL()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
    //Mac环境下必须添加这一行
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
}
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode)
{
    // 当用户按下ESC键,我们设置window窗口的WindowShouldClose属性为true
    // 关闭应用程序
    if(key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GL_TRUE);
}
void initShader()
{
    GLuint vertexShader;//定义顶点着色器对象
    vertexShader = glCreateShader(GL_VERTEX_SHADER);

    glShaderSource(vertexShader,1,&vertexShaderSource,NULL);
    glCompileShader(vertexShader);
    //编译着色器
    compileVertex(vertexShader);

    GLuint fragmentShader;
    fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    //编译片段着色器
    glShaderSource(fragmentShader,1,&fragmentShaderSource,NULL);
    glCompileShader(fragmentShader);
    compileVertex(fragmentShader);

    GLuint fragmentShaderYellow;
    fragmentShaderYellow = glCreateShader(GL_FRAGMENT_SHADER);

    glShaderSource(fragmentShaderYellow,1,&fragmentShader2Source,NULL);
    glCompileShader(fragmentShaderYellow);
    compileVertex(fragmentShaderYellow);

    //连接着色器
    shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram,vertexShader);
    glAttachShader(shaderProgram,fragmentShader);
    glLinkProgram(shaderProgram);
    detectShaderLink(shaderProgram);

    shaderProgramYellow = glCreateProgram();
    glAttachShader(shaderProgramYellow,vertexShader);
    glAttachShader(shaderProgramYellow,fragmentShaderYellow);
    glLinkProgram(shaderProgramYellow);
    detectShaderLink(shaderProgramYellow);

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);
    glDeleteShader(fragmentShaderYellow);
}
void compileVertex(GLuint vertex)
{
    GLint sucess;
    GLchar infoLog[512];
    glGetShaderiv(vertex,GL_COMPILE_STATUS,&sucess);
    if (!sucess)
    {
        glGetShaderInfoLog(vertex, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;
    }
}
void detectShaderLink(GLuint shaderProgram)
{
    GLint success;
    GLchar infoLog[512];
    glGetProgramiv(shaderProgram,GL_LINK_STATUS,&success);
    if (!success)
    {
        glGetShaderInfoLog(shaderProgram,512,NULL,infoLog);
    }
}

void renderTriangle()
{
    GLfloat vertices[] = {
        -0.5f, -0.5f, 0.0f,
        0.5f, -0.5f, 0.0f,
        0.0f,  0.5f, 0.0f
    };


    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);
    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glBindVertexArray(0);

}
void ElementBufferTest()
{

    //绘制两个三角形组成矩形，这里只存储不同的顶点
    GLfloat vertices[] = {
        0.5f, 0.5f, 0.0f,   // 右上角
        0.5f, -0.5f, 0.0f,  // 右下角
        -0.5f, -0.5f, 0.0f, // 左下角
        -0.5f, 0.5f, 0.0f   // 左上角
    };
    //绘制顺序
    GLuint indices[] = {
        0,1,3,//第一个三角形
        1,2,3 //第二个三角形
    };

    glGenVertexArrays(1,&VAO);
    glGenBuffers(1,&VBO);
    glGenBuffers(1,&EBO);

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER,VBO);
    glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_STATIC_DRAW);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(indices),indices,GL_STATIC_DRAW);

    glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,3*sizeof(GLfloat),(GLvoid*)0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER,0);

    glBindVertexArray(0);

}
void drawTwoTriangles()
{
    GLfloat vertices[] = {
        -0.9f, -0.5f, 0.0f,  // Left
        -0.0f, -0.5f, 0.0f,  // Right
        -0.45f, 0.5f, 0.0f,  // Top

        0.0f, -0.5f, 0.0f,  // Left
        0.9f, -0.5f, 0.0f,  // Right
        0.45f, 0.5f, 0.0f   // Top
    };

    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);

    glBindVertexArray(VAO);

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glBindVertexArray(0);
}
void drawTwoSameTriangles()
{
    GLfloat vertices1[] = {
        -0.9f, -0.5f, 0.0f,  // Left
        -0.0f, -0.5f, 0.0f,  // Right
        -0.45f, 0.5f, 0.0f,  // Top
    };
    GLfloat vertices2[] = {
        0.0f, -0.5f, 0.0f,  // Left
        0.9f, -0.5f, 0.0f,  // Right
        0.45f, 0.5f, 0.0f   // Top
    };

    glGenVertexArrays(NUM,VAOs);
    glGenBuffers(NUM,VBOs);

    glBindVertexArray(VAOs[0]);
    glBindBuffer(GL_ARRAY_BUFFER,VBOs[0]);
    glBufferData(GL_ARRAY_BUFFER,sizeof(vertices1),vertices1,GL_STATIC_DRAW);
    glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,3*sizeof(GLfloat),(GLvoid*)0);
    glEnableVertexAttribArray(0);
    glBindVertexArray(0);

    glBindVertexArray(VAOs[1]);
    glBindBuffer(GL_ARRAY_BUFFER,VBOs[1]);
    glBufferData(GL_ARRAY_BUFFER,sizeof(vertices2),vertices2,GL_STATIC_DRAW);
    glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,3*sizeof(GLfloat),(GLvoid*)0);
    glEnableVertexAttribArray(0);
    glBindVertexArray(0);

}

2.Function.h

//
// Function.h
// GL_example
//
// Created by LiYong on 2018/3/9.
//

#ifndef Function_h
#define Function_h
#define GLEW_STATIC


#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include "Argument.h"


using namespace std;

void initGL();
void key_callback(GLFWwindow* window, int key, int scancode, int action, int mode);
void compileVertex(GLuint vertex);
void detectShaderLink(GLuint shaderProgram);
void initShader();

//绘制三角形
void renderTriangle();
//索引缓冲对象
void ElementBufferTest();
//绘制两个连续的三角形
void drawTwoTriangles();
//创建两个相同的三角形
void drawTwoSameTriangles();
#endif /* Function_h */

3. Argument.h

//
// Argument.h
// GL_example
//
// Created by LiYong on 2018/3/9.
//

#ifndef Argument_h
#define Argument_h

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#define NUM 2

const GLchar* vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 position;\n"
"void main()\n"
"{\n"
"gl_Position = vec4(position.x, position.y, position.z, 1.0);\n"
"}\0";
const GLchar* fragmentShaderSource = "#version 330 core\n"
"out vec4 color;\n"
"void main()\n"
"{\n"
"color = vec4(1.0f, 0.5f, 0.2f, 1.0f);\n"
"}\n\0";
const GLchar* fragmentShader2Source = "#version 330 core\n"
"out vec4 color;\n"
"void main()\n"
"{\n"
"color = vec4(0.0f, 1.0f, 0.0f, 1.0f); // The color yellow \n"
"}\n\0";
GLuint VBO, VAO, EBO;
GLuint VBOs[NUM],VAOs[NUM],EBOs[NUM];
//定义着色器
GLuint shaderProgram;
GLuint shaderProgramYellow;

#endif /* Argument_h */
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