C++/OpenGL VAO 问题

问题描述

#define GLEW_STATIC
#include <GLglew.h>
#include <GLFWglfw3.h>
#include <GLglew.h>
#include <glm.hpp>
#include <iostream>
#include <fstream>
#include <string>

#define WIDTH 800
#define HEIGHT 600
#define TITLE "Dynamic"

GLFWwindow* window;
int vaoID;

float vertices[] = {-0.5f, 0.5f, 0, -0.5f, -0.5f, 0,    0.5f, 0.5f, 0,  0.5f, 0.5f, 0,  -0.5f, -0.5f,   0,  0.5f, -0.5f, 0};

void loadToVAO(float vertices[]);

void update() {
    loadToVAO(vertices);
    while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();
        glClear(GL_COLOR_BUFFER_BIT);
        glClearColor(1, 0, 0, 1);
        glDrawArrays(GL_TRIANGLES, 0, 6);
        glfwSwapBuffers(window);
    }
}

int main() {
    if (!glfwInit())
        std::cout << "Couldn't initialize GLFW!" << std::endl;

    window = glfwCreateWindow(WIDTH, HEIGHT, TITLE, NULL, NULL);
    glfwMakeContextCurrent(window);
    glfwSwapInterval(1);

    if (GLEW_OK != glewInit())
        std::cout << "GLEW fucked up!" << std::endl;

    std::cout << "Your GL version: " << glGetString(GL_VERSION) << std::endl;
    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    update();
}



void loadShaders() {

}

void loadToVAO(float vertices[]) {
    GLuint vboID;
    GLuint vaoID;
    glGenBuffers(1, &vboID);
    glBindBuffer(GL_ARRAY_BUFFER, vboID);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices) * 8, vertices, GL_STATIC_DRAW);
    glGenVertexArrays(1, &vaoID);
    glBindVertexArray(vaoID);
    std::cout << vaoID << std::endl;
    glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);
    glEnableVertexAttribArray(0);
}

这是我用于创建和渲染包含具有顶点位置的 VBO 的 VAO 的代码.但不幸的是它不起作用.它绘制一个三角形而不是一个四边形.但是当我把loadToVAO函数的代码放在while循环之前的update函数中时，它就起作用了.

This is my code for creating and rendering a VAO that contains a VBO with the vertex positions. But unfortunately it doesn't work. It draws a triangle instead of a quad. But when I put the code of the loadToVAO function in the update function before the while loop, it works.

推荐答案

sizeof 运算符始终返回基础类型的大小.当你把loadToVAO的内容复制到update函数中时，sizeof(vertices)基本上就是sizeof(float[18])，也就是数组的总大小.

The sizeof operator always returns the size of the underlying type. When you copy the content of loadToVAO to the update function, sizeof(vertices) is basically sizeof(float[18]), which is the total size of the array.

但是在 loadToVAO 中，sizeof(vertices) 将函数参数 vertices 作为输入而不是全局变量.由于在 C++ 中未定义大小的数组参数被视为我们这里的相同类型的点:

But inside the loadToVAO, the sizeof(vertices) takes the function parameter vertices as input and not the global variable. Since array parameters of undefined size in C++ are treated as points of the same type we have here:

sizeof(vertices) == sizeof(float[]) == sizeof(float*)

它是指针的大小(4 或 8)，不再是数据的大小.

which is the size of a pointer (4 or 8) and not the size of the data anymore.

要解决这个问题，您可以将数组的大小也传递给函数，这是 C 的方法.更现代的方法是首先使用 std::array 或 std::vector 来存储数据.

To solve this, you can either pass the size of the array also to the function, which is the C way to go. The more modern way is to use std::array or std::vector to store the data in the first place.

第二次查看时，我看到您首先使用了 sizeof(vertices) * 8.我不太确定 8 是从哪里来的，因为你既没有 8 个元素，浮点数也没有 8 个字节的大小.

On the second look I saw that you used sizeof(vertices) * 8 in the first place. I'm not really sure where the 8 comes from, since you neither have 8 elements nor does a float have a size of 8 bytes.

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