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執行OpenGL基礎（創建窗口，製作2D三角形，着色器等）後，我決定開始嘗試加載簡單的.obj模型。最推薦的庫是Assimp，所以我跟着some tutorials並修改我的項目加載模型。但不幸的是，模型顯示非常奇怪。我創建了下面的代碼來顯示這一點：使用Assimp和OpenGL加載和繪製.obj模型
#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;
}
當程序加載this teapot我的屏幕上看起來是這樣的：
而從更遠的另一個角度（使用更復雜的程序比上面的那個）：
在情況下，它是非常有用的，我與Nvidia的GTX 750鈦，驅動版本361.45
步幅不應爲零。你說它根本不起作用 - 如果你把步幅放在那裏作爲sizeof（Vertex）''會發生什麼？ Vertex的大小是多少（sizeof（Vertex）'返回）是什麼？ – Sam
'glVertexAttribPointer（0，...'< - 你確定索引的位置和法線真的是0和1嗎？你沒有說明你的GL版本，但是在現代版本中索引可以在着色器中分配，否則可以使用'glGetAttribLocation'來查詢位置 – SurvivalMachine
@Sam將步幅改變爲sizeof（Vertex）'確實修復了它，我想我以爲我以前在玩OpenGL的時候並沒有工作。如果你想要，你可以作出答案，我會接受:) – Orfby