[英]Trouble loading and drawing a .obj model using Assimp and OpenGL
在执行完OpenGL的基础知识(创建窗口,制作2D三角形,着色器等)之后,我决定开始尝试加载简单的.obj
模型。 最受欢迎的库是Assimp,因此我遵循了一些教程并修改了项目以加载模型。 但是不幸的是,这些模型的显示非常奇怪。 我创建了以下代码来显示这一点:
#include <iostream>
#include <string>
#include <vector>
#include <memory>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/postprocess.h>
struct Vertex
{
glm::vec3 position;
glm::vec3 normal;
};
struct Mesh
{
//The vertex array object, vertex buffer object and element buffer object
GLuint VAO;
GLuint VBO;
GLuint EBO;
//Vectors for the vertices and indices to put in the buffers
std::vector<Vertex> vertices;
std::vector<GLuint> indices;
//Constructor
Mesh(const std::vector<Vertex>& vertices, const std::vector<GLuint>& indices)
{
this->vertices = vertices;
this->indices = indices;
//Generate the VAO
glGenVertexArrays(1, &VAO);
//Generate the buffer objects
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
//Bind the VAO
glBindVertexArray(VAO);
//Bind the VBO and set the vertices
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * vertices.size(), &vertices.at(0), GL_STATIC_DRAW);
//Enable the first attribute pointer
glEnableVertexAttribArray(0);
//Set the attribute pointer The stride is meant to be 'sizeof(Vertex)', but it doesn't work at all that way
// \/
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
//Enable the second attribute pointer
glEnableVertexAttribArray(1);
//Set the attribute pointer ditto
// \/
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, (void*) offsetof(Vertex, normal));
//Bind the EBO and set the indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint) * indices.size(), &indices.at(0), GL_STATIC_DRAW);
//Report any errors
GLenum error = glGetError();
if (error != GL_NO_ERROR)
{
std::cerr << "Error while creating mesh!" << std::endl;
}
glBindVertexArray(0);
}
void draw()
{
//Bind the VAO
glBindVertexArray(VAO);
//Bind the ELement Buffer Object
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
//Draw the mesh
glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, 0);
//Unbind the VAO
glBindVertexArray(0);
}
};
int main()
{
//Intialize GLFW (no error checking for brevity)
glfwInit();
//Set the OpenGL version to 3.3
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
//Create a new window
GLFWwindow* window = glfwCreateWindow(800, 600, "Model Testing", NULL, NULL);
glfwMakeContextCurrent(window);
//Initialize glew (no checking again)
glewInit();
glViewport(0, 0, 800, 600);
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
//Load the model
Assimp::Importer importer;
const aiScene* scene = importer.ReadFile("mymodel.obj", aiProcess_Triangulate | aiProcess_GenNormals);
//Check for errors
if ((!scene) || (scene->mFlags == AI_SCENE_FLAGS_INCOMPLETE) || (!scene->mRootNode))
{
std::cerr << "Error loading mymodel.obj: " << std::string(importer.GetErrorString()) << std::endl;
//Return fail
return -1;
}
//A vector to store the meshes
std::vector<std::unique_ptr<Mesh> > meshes;
//Iterate over the meshes
for (unsigned int i = 0; i < scene->mNumMeshes; ++i)
{
//Get the mesh
aiMesh* mesh = scene->mMeshes[i];
//Create vectors for the vertices and indices
std::vector<Vertex> vertices;
std::vector<GLuint> indices;
//Iterate over the vertices of the mesh
for (unsigned int j = 0; j < mesh->mNumVertices; ++j)
{
//Create a vertex to store the mesh's vertices temporarily
Vertex tempVertex;
//Set the positions
tempVertex.position.x = mesh->mVertices[j].x;
tempVertex.position.y = mesh->mVertices[j].y;
tempVertex.position.z = mesh->mVertices[j].z;
//Set the normals
tempVertex.normal.x = mesh->mNormals[j].x;
tempVertex.normal.y = mesh->mNormals[j].y;
tempVertex.normal.z = mesh->mNormals[j].z;
//Add the vertex to the vertices vector
vertices.push_back(tempVertex);
}
//Iterate over the faces of the mesh
for (unsigned int j = 0; j < mesh->mNumFaces; ++j)
{
//Get the face
aiFace face = mesh->mFaces[j];
//Add the indices of the face to the vector
for (unsigned int k = 0; k < face.mNumIndices; ++k) {indices.push_back(face.mIndices[k]);}
}
//Create a new mesh and add it to the vector
meshes.push_back(std::unique_ptr<Mesh>(new Mesh(std::move(vertices), std::move(indices))));
}
//While the window shouldn't be closed
while (!glfwWindowShouldClose(window))
{
//Clear the buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//Draw all the meshes
for (auto& mesh : meshes) {mesh.get()->draw();}
//Swap the buffers
glfwSwapBuffers(window);
}
//Close the window now that it's not needed anymore
glfwDestroyWindow(window);
return 0;
}
当程序加载该茶壶时,我的屏幕如下所示:
并且远离另一个角度(使用比上面的程序更复杂的程序):
如果有用,我将使用Nvidia GTX 750 Ti(驱动程序版本361.45)运行Ubuntu 16.04。
步幅应为sizeof(Vertex)
。 如果不能大步向前,那其他的地方就错了!
尝试将ebo的绑定移至网格构造函数中vbo之后的右侧:
//Bind the VBO and set the vertices
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * vertices.size(), &vertices.at(0), GL_STATIC_DRAW);
//Bind the EBO and set the indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint) * indices.size(), &indices.at(0), GL_STATIC_DRAW);
那就是他们在链接的网格页面上拥有它的方式。 我在使用其他加载程序时遇到了类似的问题。 您的索引未正确加载,因此某些顶点的位置正确,而其他顶点的位置不正确。
我在OpenGL方面的经历可悲,所以我可能会误会。 我看到您的顶点是:x,y,z,nx,ny,nz其中xyz是顶点坐标,而nxnynz是法线坐标。 因此,步幅为6 * sizeof(float)。
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), 0);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), (void*) 3*sizeof(float);
只需在此处查看第二个答案: Opengl Vertex属性stride即可了解有关步幅计算的更多信息
如果这无助于检查索引的格式是否正确
小建议:使用立方体而不是茶壶(只能在搅拌机中制成立方体或自己在记事本中书写)
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