QT_OPENGL-------- 3.ElementArraryBuffer

与上一节内容基本相同，只是用ElementArraryBuffer绘制三角形，也就是VBO与IBO。

1.VBO 一系列点，通过glDrawArrays指定绘制几个点，是连续的，不能跳跃。
2.IBO（ElementArrayBufferObject） 一系列点，通过指定其中的某一些点组成三角形，不需要是连续的。
gldrawElement(绘制什么,绘制数据的个数，类型，绘制的起始位置)

3.其他与上一节相同，代码部分如下：

#include<GL/glew.h>

#include <GLFW/glfw3.h>

#include <stdio.h>

#include<iostream>

#include<glm/glm.hpp>

#include<glm/ext.hpp>

using namespace std;

struct Vertex

{

    float pos[];

    float color[];

};

char *LoadFileContent(const char*path)//加载shader

{

    FILE*pFile = fopen(path, "rb");

    if (pFile)

    {

        fseek(pFile, , SEEK_END);

        int nLen = ftell(pFile);

        char*buffer = new char[nLen+];

        rewind(pFile);

        fread(buffer, nLen , , pFile);

        buffer[nLen]='\0';

        fclose(pFile);

        return buffer;

    }

    fclose(pFile);

    return nullptr;

}

GLuint CreateGPUProgram(const char*vsShaderPath, const char*fsShaderPath)//编译shader

{

    GLuint vsShader = glCreateShader(GL_VERTEX_SHADER);

    GLuint fsShader = glCreateShader(GL_FRAGMENT_SHADER);

    const char* vsCode = LoadFileContent(vsShaderPath);

    const char* fsCode = LoadFileContent(fsShaderPath);

    glShaderSource(vsShader, , &vsCode, nullptr);

    glShaderSource(fsShader, , &fsCode, nullptr);//ram -> vram

    glCompileShader(vsShader);

    glCompileShader(fsShader);

    GLuint program = glCreateProgram();

    glAttachShader(program, vsShader);

    glAttachShader(program, fsShader);

    glLinkProgram(program);

    glDetachShader(program,vsShader);

    glDetachShader(program, fsShader);

    glDeleteShader(vsShader);

    glDeleteShader(fsShader);

    return program;

}

int main(void)

{

    GLFWwindow* window;

    /* Initialize the library */

    if (!glfwInit())

        return -;

    /* Create a windowed mode window and its OpenGL context */

    window = glfwCreateWindow(, , "Hello World", NULL, NULL);

    if (!window)

    {

        glfwTerminate();

        return -;

    }

    /* Make the window's context current */

    glfwMakeContextCurrent(window);

      //shader数据

    GLenum status = glewInit();

    if (status != GLEW_OK)

    {

        cout<<">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>"<<endl;

        std::cout << "Error::GLEW glew version:" << glewGetString(GLEW_VERSION)

            << " error string:" << glewGetErrorString(status) << std::endl;

        glfwTerminate();

        std::system("pause");

       // return -1;

    }

        GLuint program = CreateGPUProgram("/home/jun/Qt_Preject/opengl/shader/materials/sample.vs", "/home/jun/Qt_Preject/opengl/shader/materials/sample.fs");

        //取得shader变量的位置

        GLint posLocation, colorLocation, MLocation, VLocation, PLocation;

        posLocation = glGetAttribLocation(program, "pos");

        colorLocation = glGetAttribLocation(program, "color");

        MLocation = glGetUniformLocation(program, "M");

        VLocation = glGetUniformLocation(program, "V");

        PLocation = glGetUniformLocation(program, "P");

        Vertex vertex[];

        vertex[].pos[] = ;

        vertex[].pos[] = ;

        vertex[].pos[] = -100.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].pos[] = ;

        vertex[].pos[] = ;

        vertex[].pos[] = -100.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].pos[] = ;

        vertex[].pos[] = ;

        vertex[].pos[] = -100.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

        vertex[].color[] = 1.0f;

     //vbo上传shader数据到GPU

        GLuint vbo;

        glGenBuffers(, &vbo);

        glBindBuffer(GL_ARRAY_BUFFER, vbo);

        glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * , vertex, GL_STATIC_DRAW);

        glBindBuffer(GL_ARRAY_BUFFER, );

     //ibo上传shader数据到GPU

        unsigned int indexes[] = {,,};

        GLuint ibo;

        glGenBuffers(, &ibo);

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);

        glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(unsigned int) * , indexes, GL_STATIC_DRAW);

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, );

        float identity[] = {

            ,,,,

            ,,,,

            ,,,,

            ,,,

        };

        glm::mat4 projection = glm::perspective(45.0f, 800.0f / 600.0f, 0.1f, 1000.0f);

    /* Loop until the user closes the window */

    while (!glfwWindowShouldClose(window))

    {

        /* Draw a triangle */

        glUseProgram(program);

        glUniformMatrix4fv(MLocation, , GL_FALSE, identity);

        glUniformMatrix4fv(VLocation, , GL_FALSE, identity);

        glUniformMatrix4fv(PLocation, , GL_FALSE, glm::value_ptr(projection));

        glBindBuffer(GL_ARRAY_BUFFER, vbo);

        glEnableVertexAttribArray(posLocation);

        glVertexAttribPointer(posLocation, , GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*));

        glEnableVertexAttribArray(colorLocation);

        glVertexAttribPointer(colorLocation, , GL_FLOAT, GL_FALSE, sizeof(Vertex), (void*)(sizeof(float)*));

        //glDrawArrays(GL_TRIANGLES, 0, 3);

       //glBindBuffer(GL_ARRAY_BUFFER, 0);

        glBindBuffer(GL_ARRAY_BUFFER, );

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);

        glDrawElements(GL_TRIANGLES, , GL_UNSIGNED_INT, );

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, );

        glUseProgram();

        /* Swap front and back buffers */

        glfwSwapBuffers(window);

        /* Poll for and process events */

        glfwPollEvents();

    }

    glfwTerminate();

    return ;

}

效果和上一节一样。