OpenGL笔记八之EBO和EBO绘制流程

—— 2024-07-07 晚上

总结自bilibili赵新政老师的教程

code review!

1.EBO

代码

void prepareVAO() {//1 准备positionsfloat positions[] = {-0.5f, -0.5f, 0.0f,0.5f, -0.5f, 0.0f,0.0f,  0.5f, 0.0f,0.5f,  0.5f, 0.0f,};unsigned int indices[] = {0, 1, 2,2, 1, 3};//2 VBO创建GLuint vbo;glGenBuffers(1, &vbo);glBindBuffer(GL_ARRAY_BUFFER, vbo);glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);//3 EBO创建GLuint ebo;glGenBuffers(1, &ebo);glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);//4 VAO创建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, vbo);glEnableVertexAttribArray(0);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 3, (void*)0);//5.2 加入ebo到当前的vaoglBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);glBindVertexArray(0);
}

对比VAO

2.glDrawElements：如果使用了ebo，最后一个参数可以写0

运行

关键代码

//	glDrawArrays(GL_LINE_STRIP, 0, 6);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
//  glBindVertexArray(0);

3.glDrawElements：如果使用了ebo，假设最后一个参数是数字，表示ebo内偏移量

3.1.count改为3，偏移量为0

运行

关键代码

glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0);

3.2.count改为3，偏移量为3

运行

关键代码

glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, (void*)(sizeof(int)*3));

4.glDrawElements：如果没有使用ebo，可以直接将cpu端的indices数组传输进去(不推荐这种方式)

运行

关键代码

//5.2 加入ebo到当前的vao
// glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo); //需要注释掉

unsigned int indices[] = {0, 1, 2,2, 1, 3
};
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, indices);

5.main.cpp

代码

#include <iostream>#define DEBUG//注意：glad头文件必须在glfw引用之前引用
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <string>
#include <assert.h>//断言
#include "wrapper/checkError.h"
#include "application/Application.h"/*
*┌────────────────────────────────────────────────┐
*│　目	   标： 学习EBO进行绘制
*│　讲    师： 赵新政(Carma Zhao)
*│　拆分目标：
*│
*│　		1 创建EBO，灌入数据，与vao绑定
*│　		2 练习glDrawElements
*				-如果使用了ebo，最后一个参数可以写0；
*				-如果使用了ebo，假设最后一个参数是数字，表示ebo内偏移量
*				-如果没有使用ebo，可以直接将cpu端的indices数组传输进去
*└────────────────────────────────────────────────┘
*/GLuint vao, program;void OnResize(int width, int height) {GL_CALL(glViewport(0, 0, width, height));std::cout << "OnResize" << std::endl;
}void OnKey(int key, int action, int mods) {std::cout << key << std::endl;
}void prepareVAO() {//1 准备positionsfloat positions[] = {-0.5f, -0.5f, 0.0f,0.5f, -0.5f, 0.0f,0.0f,  0.5f, 0.0f,0.5f,  0.5f, 0.0f,};unsigned int indices[] = {0, 1, 2,2, 1, 3};//2 VBO创建GLuint vbo;glGenBuffers(1, &vbo);glBindBuffer(GL_ARRAY_BUFFER, vbo);glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);//3 EBO创建GLuint ebo;glGenBuffers(1, &ebo);glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);//4 VAO创建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, vbo);glEnableVertexAttribArray(0);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(float) * 3, (void*)0);//5.2 加入ebo到当前的vaoglBindBuffer(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""void main()\n""{\n""   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n""}\0";const char* fragmentShaderSource ="#version 330 core\n""out vec4 FragColor;\n""void main()\n""{\n""   FragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);\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 render() {//执行opengl画布清理操作GL_CALL(glClear(GL_COLOR_BUFFER_BIT));//1 绑定当前的programGL_CALL(glUseProgram(program));//2 绑定当前的vaoGL_CALL(glBindVertexArray(vao));//3 发出绘制指令
//	glDrawArrays(GL_LINE_STRIP, 0, 6);glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);glBindVertexArray(0);
}int main() {if (!app->init(800, 600)) {return -1;}app->setResizeCallback(OnResize);app->setKeyBoardCallback(OnKey);//设置opengl视口以及清理颜色GL_CALL(glViewport(0, 0, 800, 600));GL_CALL(glClearColor(0.2f, 0.3f, 0.3f, 1.0f));prepareShader();prepareVAO();while (app->update()) {render();}app->destroy();return 0;
}