Импортированная модель OpenGL Assimp не отображается

gl::DrawElements(gl::ELEMENT_ARRAY_BUFFER, numOfIndices, gl::UNSIGNED_INT, (void*)0);
                 ^^^^^^^^^^^^^^^^^^^^^^^^ huh?

GL_ELEMENT_ARRAY_BUFFER никогда не был веским аргументом в пользу glDrawElements().

Попробуйте что-нибудь вроде GL_TRIANGLES:

// OpenGL
#include <GL/glew.h>
#include <GLFW/glfw3.h>

// GLM
#include <glm/glm.hpp>
#include <glm/gtx/transform.hpp>
#include <glm/gtc/type_ptr.hpp>

// SOIL
#include <SOIL/SOIL.h>

// assimp
#include <assimp/Importer.hpp>
#include <assimp/scene.h>
#include <assimp/postprocess.h>

// STL
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <vector>

float deltaTime = 1.0f / 60.0f;

GLFWwindow *window;
int windowWidth = 640;
int windowHeight = 480;

GLuint program;
GLuint mvpUniform;
glm::mat4 modelMatrix;
glm::mat4 viewMatrix;
glm::mat4 projectionMatrix;

double mouseX, mouseY;
float speed = 0.09f;
float mouseSpeed = 0.04f;

glm::vec3 position = glm::vec3(0, 0, 5);
glm::vec3 direction, right, up;

float horizontalAngle = 3.14159f;
float verticalAngle = 0.0f;
float fov = 60.0f;

bool wKeyPressed;
bool sKeyPressed;
bool aKeyPressed;
bool dKeyPressed;

void initialize() 
{
    // Initialize GLFW
    if (!glfwInit()) 
    {
        std::cout << "Error: GLFW failed to initialize.\n";
        return;
    }

    // Create window
    window = glfwCreateWindow(windowWidth, windowHeight, "OpenGL Hacks", NULL, NULL);
    if (!window) 
    {
        std::cout << "Error: Failed to create window.\n";
        glfwTerminate();
        return;
    }
    glfwMakeContextCurrent(window);

    // Load OpenGL functions
    if( GLEW_OK != glewInit() )
    {
        std::cout << "Error: Failed to load OpenGL functions.\n";
        glfwTerminate();
        return;
    }
}

void windowSizeChange(GLFWwindow *window, int width, int height) 
{
    if (windowWidth != width || windowHeight != height)
    {
        windowWidth = width;
        windowHeight = height;

        projectionMatrix = glm::perspective
            (
            fov,
            (float)windowWidth / windowHeight,
            0.1f,
            100.0f
            );

        glUseProgram(program);
        glUniformMatrix4fv(mvpUniform, 1, GL_FALSE, glm::value_ptr(projectionMatrix));
        glUseProgram(0);

        glViewport(0, 0, (GLsizei)width, (GLsizei)height);
    }
}

void handleKeyboardInput(GLFWwindow *window, int key, int scancode, int action, int mods) 
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, 1);
    else if (key == GLFW_KEY_W && action == GLFW_PRESS)
        wKeyPressed = true;
    else if (key == GLFW_KEY_S && action == GLFW_PRESS)
        sKeyPressed = true;
    else if (key == GLFW_KEY_A && action == GLFW_PRESS)
        aKeyPressed = true;
    else if (key == GLFW_KEY_D && action == GLFW_PRESS)
        dKeyPressed = true;
    else if (key == GLFW_KEY_W && action == GLFW_RELEASE)
        wKeyPressed = false;
    else if (key == GLFW_KEY_S && action == GLFW_RELEASE)
        sKeyPressed = false;
    else if (key == GLFW_KEY_A && action == GLFW_RELEASE)
        aKeyPressed = false;
    else if (key == GLFW_KEY_D && action == GLFW_RELEASE)
        dKeyPressed = false;
}

void getInput() 
{
    if (wKeyPressed)
        position += direction * deltaTime * speed;
    if (sKeyPressed)
        position -= direction * deltaTime * speed;
    if (aKeyPressed)
        position -= right * deltaTime * speed;
    if (dKeyPressed)
        position += right * deltaTime * speed;

    direction = glm::vec3
        (
        std::cos(verticalAngle) * std::sin(horizontalAngle),
        std::sin(verticalAngle),
        std::cos(verticalAngle) * std::cos(horizontalAngle)
        );
    right = glm::vec3
        (
        std::sin(horizontalAngle - 3.14159f / 2.0f),
        0.0f,
        std::cos(horizontalAngle - 3.14159f / 2.0f)
        );
    up = glm::cross(right, direction);

    glfwGetCursorPos(window, &mouseX, &mouseY);
    glfwSetCursorPos(window, windowWidth / 2, windowHeight / 2);
    horizontalAngle += mouseSpeed * deltaTime * float(windowWidth / 2 - mouseX);
    // Prevent from going upside down
    if (!up.y >= -0.5f)
        verticalAngle += mouseSpeed * deltaTime * float(windowHeight / 2 - mouseY);
    else if (up.y == -1.0f)
        up = glm::vec3(up.x, 1, up.z);
}

GLuint loadImage()
{
    GLuint textureID;
    glGenTextures(1, &textureID);
    glBindTexture(GL_TEXTURE_2D, textureID);

    unsigned char bytes[] = 
    {
        255, 0, 0,
        0, 255, 0,
        0, 0, 255,
        255, 255, 0
    };

    textureID = SOIL_create_OGL_texture
        (
        bytes, 
        2, 2, 3,
        textureID,
        SOIL_FLAG_MIPMAPS | SOIL_FLAG_INVERT_Y
        );

    glBindTexture(GL_TEXTURE_2D, 0);
    if (textureID == 0)
        printf("SOIL Loading Error: %s\n", SOIL_last_result());

    return textureID;
}

void loadOBJ
    (
    const char *path,
    std::vector<unsigned int> &outIndices,
    std::vector<float> &outVertices,
    std::vector<float> &outUVs,
    std::vector<float> &outNormals
    ) {

    Assimp::Importer importer;
    const aiScene* scene = importer.ReadFile(path, aiProcessPreset_TargetRealtime_Fast);
    aiMesh* mesh = scene->mMeshes[0];

    int numOfFaces = mesh->mNumFaces;
    int numOfIndices = numOfFaces * 3;
    outIndices.resize(numOfIndices);

    for (unsigned int i = 0; i < mesh->mNumFaces; ++i) {
        const aiFace &face = mesh->mFaces[i];
        assert(face.mNumIndices == 3);
        outIndices[i * 3 + 0] = face.mIndices[0];
        outIndices[i * 3 + 1] = face.mIndices[1];
        outIndices[i * 3 + 2] = face.mIndices[2];
    }

    int numOfVertices = mesh->mNumVertices;
    outVertices.resize(numOfVertices * 3);
    outNormals.resize(numOfVertices * 3);
    outUVs.resize(numOfVertices * 2);
    for (unsigned int i = 0; i < mesh->mNumVertices; ++i) {
        if (mesh->HasPositions()) {
            outVertices[i * 3 + 0] = mesh->mVertices[i].x;
            outVertices[i * 3 + 1] = mesh->mVertices[i].y;
            outVertices[i * 3 + 2] = mesh->mVertices[i].z;
        }

        if (mesh->HasNormals()) {
            outNormals[i * 3 + 0] = mesh->mNormals[i].x;
            outNormals[i * 3 + 1] = mesh->mNormals[i].x;
            outNormals[i * 3 + 2] = mesh->mNormals[i].x;
        }

        if (mesh->HasTextureCoords(0)) {
            outUVs[i * 2 + 0] = mesh->mTextureCoords[0][i].x;
            outUVs[i * 2 + 1] = mesh->mTextureCoords[0][i].y;
        }
    }
}

// GLSL shader program loader
struct Program
{
    static GLuint Load( const char* vert, const char* geom, const char* frag )
    {
        GLuint prog = glCreateProgram();
        if( vert ) AttachShader( prog, GL_VERTEX_SHADER, vert );
        if( geom ) AttachShader( prog, GL_GEOMETRY_SHADER, geom );
        if( frag ) AttachShader( prog, GL_FRAGMENT_SHADER, frag );
        glLinkProgram( prog );
        CheckStatus( prog );
        return prog;
    }

private:
    static void CheckStatus( GLuint obj )
    {
        GLint status = GL_FALSE, len = 10;
        if( glIsShader(obj) )   glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
        if( glIsProgram(obj) )  glGetProgramiv( obj, GL_LINK_STATUS, &status );
        if( status == GL_TRUE ) return;
        if( glIsShader(obj) )   glGetShaderiv( obj, GL_INFO_LOG_LENGTH, &len );
        if( glIsProgram(obj) )  glGetProgramiv( obj, GL_INFO_LOG_LENGTH, &len );
        std::vector< char > log( len, 'X' );
        if( glIsShader(obj) )   glGetShaderInfoLog( obj, len, NULL, &log[0] );
        if( glIsProgram(obj) )  glGetProgramInfoLog( obj, len, NULL, &log[0] );
        std::cerr << &log[0] << std::endl;
        exit( -1 );
    }

    static void AttachShader( GLuint program, GLenum type, const char* src )
    {
        GLuint shader = glCreateShader( type );
        glShaderSource( shader, 1, &src, NULL );
        glCompileShader( shader );
        CheckStatus( shader );
        glAttachShader( program, shader );
        glDeleteShader( shader );
    }
};
#define GLSL(version, shader) "#version " #version "\n" #shader

const char* vert = GLSL
(
    330 core,
    layout (location = 0) in vec3 position_modelspace;
    layout (location = 1) in vec2 uv;
    layout (location = 2) in vec3 normal_modelspace;

    out vec2 UV;
    out vec3 Position_worldspace;
    out vec3 Normal_cameraspace;
    out vec3 EyeDirection_cameraspace;
    out vec3 LightDirection_cameraspace;

    uniform mat4 mvp;
    uniform mat4 viewMatrix;
    uniform mat4 modelMatrix;
    uniform vec3 lightPosition_worldspace;

    void main() 
    {
        gl_Position = mvp * vec4(position_modelspace, 1.0f);

        Position_worldspace = (modelMatrix * vec4(position_modelspace, 1.0f)).xyz;

        vec3 position_modelspaceCamera = (viewMatrix * modelMatrix * vec4(position_modelspace, 1.0f)).xyz;
        EyeDirection_cameraspace = vec3(0, 0, 0) - position_modelspaceCamera;

        vec3 lightPosition_worldspaceCamera = (viewMatrix * vec4(lightPosition_worldspace, 1.0f)).xyz;
        LightDirection_cameraspace = lightPosition_worldspaceCamera + EyeDirection_cameraspace;

        Normal_cameraspace = (viewMatrix * modelMatrix * vec4(normal_modelspace, 0.0f)).xyz;
        UV = uv;
    }
);

const char* frag = GLSL
(
    330 core,
    in vec2 UV;
    in vec3 Position_worldspace;
    in vec3 Normal_cameraspace;
    in vec3 EyeDirection_cameraspace;
    in vec3 LightDirection_cameraspace;

    out vec3 color;

    uniform sampler2D textureSampler;
    uniform mat4 modelViewMatrix;
    uniform vec3 lightPosition_worldspace;

    void main()
    {
        vec3 lightColor = vec3(1, 1, 1);
        float lightPower = 50.0f;

        vec3 materialDiffuseColor = texture2D(textureSampler, UV).rgb;
        vec3 materialAmbientColor = vec3(0.1, 0.1, 0.1) * materialDiffuseColor;
        vec3 materialSpecularColor = vec3(0.3, 0.3, 0.3);

        float distance = length(lightPosition_worldspace - Position_worldspace);

        vec3 n = normalize(Normal_cameraspace);
        vec3 l = normalize(LightDirection_cameraspace);

        float cosTheta = clamp(dot(n, l), 0, 1);

        vec3 eye = normalize(EyeDirection_cameraspace);
        vec3 reflection = reflect(-l, n);

        float cosAlpha = clamp(dot(eye, reflection), 0, 1);

        color = materialAmbientColor +
                materialDiffuseColor * lightColor * lightPower * cosTheta / (distance * distance) +
                materialSpecularColor * lightColor * lightPower * pow(cosAlpha, 5) / (distance * distance);
    }
);



int main(int argc, char *argv[]) 
{
    initialize();
    glfwSetWindowSizeCallback(window, windowSizeChange);
    glfwSetKeyCallback(window, handleKeyboardInput);

    // Z order buffering
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LESS);

    // Vertex Array Object
    GLuint vertexArrayObject;
    glGenVertexArrays(1, &vertexArrayObject);
    glBindVertexArray(vertexArrayObject);

    program = Program::Load( vert, NULL, frag );
    mvpUniform = glGetUniformLocation(program, "mvp");
    GLuint modelMatrixUniform = glGetUniformLocation(program, "modelMatrix");
    GLuint viewMatrixUniform = glGetUniformLocation(program, "viewMatrix");
    GLuint lightPositionUniform = glGetUniformLocation(program, "lightPosition_worldspace");

    GLuint texture = loadImage();
    GLuint textureSamplerUniform = glGetUniformLocation(program, "textureSampler");

    std::vector<unsigned int> indices;
    std::vector<float> vertices;
    std::vector<float> uvs;
    std::vector<float> normals;
    loadOBJ("cube.obj", indices, vertices, uvs, normals);

    GLuint elementBuffer;
    glGenBuffers(1, &elementBuffer);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementBuffer);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned int), &indices[0], GL_STATIC_DRAW);

    GLuint vertexBuffer;
    glGenBuffers(1, &vertexBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
    glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(aiVector3D), &vertices[0], GL_STATIC_DRAW);

    GLuint uvBuffer;
    glGenBuffers(1, &uvBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, uvBuffer);
    glBufferData(GL_ARRAY_BUFFER, uvs.size() * sizeof(aiVector2D), &uvs[0], GL_STATIC_DRAW);

    GLuint normalBuffer;
    glGenBuffers(1, &normalBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, normalBuffer);
    glBufferData(GL_ARRAY_BUFFER, normals.size() * sizeof(aiVector3D), &normals[0], GL_STATIC_DRAW);

    while (!glfwWindowShouldClose(window))
    {
        getInput();

        projectionMatrix = glm::perspective(fov, (float)windowWidth / windowHeight, 0.1f, 1000.0f);
        viewMatrix = glm::lookAt(position, position + direction, up);
        modelMatrix = glm::mat4(1.0f);

        // This is actually model -> view -> projection, not the other way around
        glm::mat4 mvp = projectionMatrix * viewMatrix * modelMatrix;

        glfwPollEvents();

        // Clear screen
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glUseProgram(program);
        glUniformMatrix4fv(mvpUniform, 1, GL_FALSE, glm::value_ptr(mvp));
        glUniformMatrix4fv(modelMatrixUniform, 1, GL_FALSE, glm::value_ptr(modelMatrix));
        glUniformMatrix4fv(viewMatrixUniform, 1, GL_FALSE, glm::value_ptr(viewMatrix));

        glm::vec3 lightPosition = glm::vec3(4, 4, 4);
        glUniform3f(lightPositionUniform, lightPosition.x, lightPosition.y, lightPosition.z);

        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, texture);
        glUniform1i(textureSamplerUniform, 0);

        glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

        glBindBuffer(GL_ARRAY_BUFFER, uvBuffer);
        glEnableVertexAttribArray(1);
        glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, (void*)0);

        glBindBuffer(GL_ARRAY_BUFFER, normalBuffer);
        glEnableVertexAttribArray(2);
        glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementBuffer);
        glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, (void*)0);

        glDisableVertexAttribArray(0);
        glDisableVertexAttribArray(1);
        glDisableVertexAttribArray(2);

        glfwSwapBuffers(window);
    }

    glDeleteProgram(program);
    glDeleteBuffers(1, &vertexBuffer);
    glDeleteBuffers(1, &uvBuffer);
    glDeleteBuffers(1, &normalBuffer);
    glDeleteTextures(1, &texture);
    glDeleteVertexArrays(1, &vertexArrayObject);

    glfwDestroyWindow(window);
    glfwTerminate();
    return 0;
}

cube.obj:

# Blender3D v249 OBJ File: untitled.blend
# www.blender3d.org
mtllib cube.mtl
v 1.000000 -1.000000 -1.000000
v 1.000000 -1.000000 1.000000
v -1.000000 -1.000000 1.000000
v -1.000000 -1.000000 -1.000000
v 1.000000 1.000000 -1.000000
v 0.999999 1.000000 1.000001
v -1.000000 1.000000 1.000000
v -1.000000 1.000000 -1.000000
vt 0.748573 0.750412
vt 0.749279 0.501284
vt 0.999110 0.501077
vt 0.999455 0.750380
vt 0.250471 0.500702
vt 0.249682 0.749677
vt 0.001085 0.750380
vt 0.001517 0.499994
vt 0.499422 0.500239
vt 0.500149 0.750166
vt 0.748355 0.998230
vt 0.500193 0.998728
vt 0.498993 0.250415
vt 0.748953 0.250920
vn 0.000000 0.000000 -1.000000
vn -1.000000 -0.000000 -0.000000
vn -0.000000 -0.000000 1.000000
vn -0.000001 0.000000 1.000000
vn 1.000000 -0.000000 0.000000
vn 1.000000 0.000000 0.000001
vn 0.000000 1.000000 -0.000000
vn -0.000000 -1.000000 0.000000
usemtl Material_ray.png
s off
f 5/1/1 1/2/1 4/3/1
f 5/1/1 4/3/1 8/4/1
f 3/5/2 7/6/2 8/7/2
f 3/5/2 8/7/2 4/8/2
f 2/9/3 6/10/3 3/5/3
f 6/10/4 7/6/4 3/5/4
f 1/2/5 5/1/5 2/9/5
f 5/1/6 6/10/6 2/9/6
f 5/1/7 8/11/7 6/10/7
f 8/11/7 7/12/7 6/10/7
f 1/2/8 2/9/8 3/13/8
f 1/2/8 3/13/8 4/14/8