OpenGL not drawing in 3D with depth buffers enabled

Question

I've spent 2 weeks trying to get OpenGL to draw a cube in 3D, but no matter what I do, it never actually drew a cube. If I enable the depth test with glEnable(DEPTH_TEST), it simply does not render anything. If I comment out that function, it renders all the vertices as if the z-values were all 0. I'm completely stuck and have no idea what i've done wrong.

Here's my main file: https://pastebin.com/D8cEcJ4g

#include "Dependencies\glew\glew.h"
#include "Dependencies\freeglut\freeglut.h"
#include "Dependencies\soil\SOIL.h"
 
#include "glm/glm.hpp"
#include "glm/gtc/matrix_transform.hpp"
#include "glm/gtc/type_ptr.hpp"
 
#include <iostream>
 
#include "ShaderLoader.h";
#include "Camera.h"
 
#define BUTTON_UP   0
#define BUTTON_DOWN 1
 
GLuint program;
GLuint vao, vbo, ebo;
GLuint texture, texture2;
 
unsigned char keyState[255];
 
 
glm::vec3 vPosTrans = glm::vec3(-0.50f, -0.50f, 0.0f);//source
glm::vec3 vPosInit = vPosTrans;
glm::vec3 vPosDest = glm::vec3(0.50f, 0.50f, 0.0f);//destination
glm::vec3 vCurrentPos = vPosTrans;
 
bool Dest1or2 = true;
 
const GLfloat WIDTH = 800.0f, HEIGHT = 600.0f;
 
Camera* camera;
 
void init(){
    camera = new Camera(180.0f, WIDTH, HEIGHT, 0.0f, 100.0f);
 
    ShaderLoader shaderLoader;
    program = shaderLoader.CreateProgram("CoordSystem_Texture_QUAD.vs", "CoordSystem_Texture_QUAD.fs");
 
    glEnable(GL_DEPTH_TEST);
 
    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
 
    // Set up vertex data (and buffer(s)) and attribute pointers
    GLfloat vertices[] = {
 
        //position              //color                 //texture coord   //Normals
        -1.01f, -1.01f, -1.01f, 1.0f, 0.0f, 0.0f,       0.0f, 1.0f,
        -1.01f, 1.01f, -1.01f,      0.0f, 1.0f, -0.0f,      0.0f, 0.0f,
        1.01f, 1.01f, -1.01f,       1.0f, 0.0f, -0.0f,      1.0f, 0.0f,
        1.01f, -1.01f, -1.01f,      0.0f, 1.0f,  1.0f,      1.0f, 1.0f,
 
        // Fill in the back face vertex data.
        -1.01f, -1.01f, 1.01f,      0.0f, 1.0f, 1.0f,       1.0f, 1.0f,
        1.01f, -1.01f, 1.01f,       1.0f, 0.0f, 1.0f,       0.0f, 1.0f,
        1.01f, 1.01f, 1.01f,        1.0f, 0.0f, 1.0f,       0.0f, 0.0f,
        -1.01f, 1.01f, 1.01f,       1.0f, 1.0f, 0.0f,       1.0f, 0.0f,
 
        // Fill in the top face vertex data.
        -1.01f, 1.01f, -1.01f,      0.0f, 1.0f, 0.0f,       0.0f, 1.0f,
        -1.01f, 1.01f, 1.01f,       1.0f, 0.0f, 1.0f,       0.0f, 0.0f,
        1.01f, 1.01f, 1.01f,        0.0f, 1.0f, 1.0f,       1.0f, 0.0f,
        1.01f, 1.01f, -1.01f,       1.0f, 1.0f, 0.0f,       1.0f, 1.0f,
 
        // Fill in the bottom face vertex data.
        -1.01f, -1.01f, -1.01f, 1.0f,  1.0f, 0.0f,      1.0f, 1.0f,
        1.01f, -1.01f, -1.01f,      0.0f,  1.0f, 1.0f,      0.0f, 1.0f,
        1.01f, -1.01f, 1.01f,       0.0f,  1.0f, 0.0f,      0.0f, 0.0f,
        -1.01f, -1.01f, 1.01f,      1.0f,  1.0f, 0.0f,      1.0f, 0.0f,
 
        // Fill in the left face vertex data.
        -1.01f, -1.01f, 1.01f,       1.0f, 1.0f, 0.0f,      0.0f, 1.0f,
        -1.01f, 1.01f, 1.01f,        1.0f, 0.0f, 1.0f,      0.0f, 0.0f,
        -1.01f, 1.01f, -1.01f,       1.0f, 0.0f, 1.0f,      1.0f, 0.0f,
        -1.01f, -1.01f, -1.01f,  1.0f, 1.0f, 0.0f,      1.0f, 1.0f,
 
        // Fill in the right face vertex data.
        1.01f, -1.01f, -1.01f,      1.0f, 1.0f, 0.0f,       0.0f, 1.0f,
        1.01f, 1.01f, -1.01f,       0.0f, 1.0f, 1.0f,       0.0f, 0.0f,
        1.01f, 1.01f, 1.01f,        1.0f, 0.0f, 1.0f,       1.0f, 0.0f,
        1.01f, -1.01f, 1.01f,       0.0f, 1.0f, 1.0f,       1.0f, 1.0f,
    };
 
    GLuint indices[] = {
        // front
        0, 1, 2,
        0, 2, 3,
        // top
        4, 5, 6,
        4, 6, 7,
        // back
        8, 9, 10,
        8, 10, 11,
        // bottom
        12, 13, 14,
        12, 14, 15,
        // left
        16, 17, 18,
        16, 18, 19,
        // right
        20, 21, 22,
        20, 22, 23,
    };
 
    //** VAO **
    // Generate vertex arrow object
    glGenVertexArrays(1, &vao);
    // Bind the Vertex Array Object to openGl context
    glBindVertexArray(vao);//otherwise glVertexAttribPointer
 
    //** VBO **
    // Then bind and set vertex buffer(s).
    // First paramter is how many buffers we have to create
    glGenBuffers(1, &vbo);
 
    // bind VBO to binding point, here it is GL_ARRAY_BUFFER
    // there are other binding points
    glBindBuffer(GL_ARRAY_BUFFER, vbo);//bind to context
    glBufferData(GL_ARRAY_BUFFER,
        sizeof(vertices),// GPU need to know how much memory needs to be allocated
        vertices,//copy data to GPU
        GL_STATIC_DRAW);// How to use the buffer - buffer is created and modified once
 
    //** EBO **
    glGenBuffers(1, &ebo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER,
        sizeof(indices),
        indices,
        GL_STATIC_DRAW);
 
 
    // ** Attributes **
 
    //** Vertex Attribute **
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);
 
    //** Color Attribute **
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(1);
 
    //** TexCoord attribute **
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
    glEnableVertexAttribArray(2);
 
    // It's always a good thing to unbind any buffer/array to prevent strange bugs
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);
 
    //** Load and bind texture 1 
    //--------------------------
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
 
 
    //** loadImage and create texture
    // Load image, create texture and generate mipmaps
    int width, height;
    unsigned char* image = SOIL_load_image("wall.jpg", &width, &height, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image);
    glBindTexture(GL_TEXTURE_2D, 0);
 
 
    // ** Load and Bind Texture 2
    //---------------------------
    glGenTextures(1, &texture2);
    glBindTexture(GL_TEXTURE_2D, texture2);
 
 
    //** loadImage and create texture
    // Load image, create texture and generate mipmaps
    unsigned char* image2 = SOIL_load_image("awesomeface.png", &width, &height, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image2);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image2);
    glBindTexture(GL_TEXTURE_2D, 0);
 
 
    // Set texture wrapping to GL_REPEAT (usually basic wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // Set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 
}
 
void render(){
 
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
    // Draw our first triangle
    glUseProgram(program);
 
    //bind 
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture);
    glUniform1i(glGetUniformLocation(program, "Texture"), 0);
 
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, texture2);
    glUniform1i(glGetUniformLocation(program, "Texture2"), 1);
 
    glBindVertexArray(vao);
 
    // Draw Elements intead of vertex array 
    glDrawArrays(GL_QUADS, 0, 24);
    //glDrawElements(GL_TRIANGLES, 24, GL_UNSIGNED_INT, 0);
    glBindVertexArray(0);
 
    glutSwapBuffers();
}
 
void update(){
    GLfloat cameraSpeed = 0.05f;
    camera->setCameraSpeed(cameraSpeed);
 
    //currentTime uniform
    GLfloat currentTime = glutGet(GLUT_ELAPSED_TIME);
    currentTime = currentTime / 1000;
    GLint currentTimeLocation = glGetUniformLocation(program, "currentTime");
    glUniform1f(currentTimeLocation, currentTime);
 
    //transforms
    glm::mat4 transform = glm::mat4(1.0f);
    glm::vec3 vScaleVec = glm::vec3(0.51f, 0.51f, 0.0f);
 
    glm::mat4 model = glm::mat4(1.0);
 
    if (keyState[(unsigned char)'w'] == BUTTON_DOWN) {
        camera->moveForward();
        std::cout << "e";
    }
    if (keyState[(unsigned char)'s'] == BUTTON_DOWN) {
        camera->moveBack();
        std::cout << "A";
    }
 
    camera->Update();
 
    //glm::mat4 projection = glm::perspective(45.0f, (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);
    glm::mat4 projection = camera->getProjectionMatrix();
 
    glm::mat4 view = glm::lookAt(camera->getCameraPos(), camera->getCameraPos() + camera->getCameraFront(), camera->getCameraUp());
 
    //glm::mat4 view = glm::lookAt(glm::vec3(1, 1, 0), glm::vec3(0, 1, 0), glm::vec3(0, 0, 1));
 
    GLfloat radius = 3.5f;
    GLfloat camX = sin(currentTime) * radius;
    GLfloat camZ = cos(currentTime) * radius;
 
    //glm::mat4 view = glm::lookAt(
    //     glm::vec3(camX, 0.0, camZ),
    //     glm::vec3(0.0, 0.0, 0.0),
    //     glm::vec3(0.0, 1.0, 0.0));
 
    transform = glm::scale(transform, vScaleVec);
    glm::vec3(0.65f, 0.65f, 0.65f);
    //transform = glm::rotate(transform, 90.0f, glm::vec3(0.0, 0.0, 1.0));
    if (vCurrentPos == vPosDest && Dest1or2 == true )
    {       
        Dest1or2 = false;
    }
    else if (vCurrentPos == vPosTrans && Dest1or2 == false)
    {
        Dest1or2 = true;
    }
    if(Dest1or2)
    vCurrentPos = glm::mix(vCurrentPos, vPosDest, currentTime * 0.01f);
    else 
    vCurrentPos = glm::mix(vCurrentPos, vPosTrans, currentTime*0.01f);
 
    //transform = glm::translate(transform, vCurrentPos);
    //transform = glm::translate(transform, glm::vec3(-0.51f, -0.51f, 0.0f));
    //transform = glm::rotate(transform, ((GLfloat)currentTime / 100) * 90.0f, glm::vec3(0.0f, 0.0f, 1.0f));
 
    // RTS
    GLuint transformLoc = glGetUniformLocation(program, "transform");
    glUniformMatrix4fv(transformLoc, 1, GL_FALSE, glm::value_ptr(transform));
 
    GLint modelLoc = glGetUniformLocation(program, "model");
    GLint viewLoc = glGetUniformLocation(program, "view");
    GLint projLoc = glGetUniformLocation(program, "projection");
 
    // Pass them to the shaders
    glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
    glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(camera->getViewMatrix()));
    glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(camera->getProjectionMatrix()));
    //glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
    //glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));
 
 
    glutPostRedisplay();
}
 
void keyboard(unsigned char key, int x, int y) {
    keyState[key] = BUTTON_DOWN;
 
    //printf("key pressed: %d \n", key);
}
 
void keyboard_up(unsigned char key, int x, int y) {
    keyState[key] = BUTTON_UP;
}
 
int main(int argc, char **argv){
 
    // init glut
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
 
    glutInitWindowPosition(300, 200);
    glutInitWindowSize(800, 600);
    glutCreateWindow("QUAD EBO");
 
    //init GLEW
    glewInit();
 
    init();
 
    //clear
    glClearColor(1.0, 0.0, 0.0, 1.0);//clear red
 
    // register callbacks
    glutDisplayFunc(render);
 
    glutKeyboardFunc(keyboard);
    glutKeyboardUpFunc(keyboard_up);
 
    glutIdleFunc(update);
 
    glutMainLoop();
 
    return 0;
}
 
 
RAW Paste Data
#include "Dependencies\glew\glew.h"
#include "Dependencies\freeglut\freeglut.h"
#include "Dependencies\soil\SOIL.h"

#include "glm/glm.hpp"
#include "glm/gtc/matrix_transform.hpp"
#include "glm/gtc/type_ptr.hpp"

#include <iostream>

#include "ShaderLoader.h";
#include "Camera.h"

#define BUTTON_UP   0
#define BUTTON_DOWN 1

GLuint program;
GLuint vao, vbo, ebo;
GLuint texture, texture2;

unsigned char keyState[255];


glm::vec3 vPosTrans = glm::vec3(-0.50f, -0.50f, 0.0f);//source
glm::vec3 vPosInit = vPosTrans;
glm::vec3 vPosDest = glm::vec3(0.50f, 0.50f, 0.0f);//destination
glm::vec3 vCurrentPos = vPosTrans;

bool Dest1or2 = true;

const GLfloat WIDTH = 800.0f, HEIGHT = 600.0f;

Camera* camera;

void init(){
    camera = new Camera(180.0f, WIDTH, HEIGHT, 0.0f, 100.0f);

    ShaderLoader shaderLoader;
    program = shaderLoader.CreateProgram("CoordSystem_Texture_QUAD.vs", "CoordSystem_Texture_QUAD.fs");

    glEnable(GL_DEPTH_TEST);

    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

    // Set up vertex data (and buffer(s)) and attribute pointers
    GLfloat vertices[] = {

        //position              //color                 //texture coord   //Normals
        -1.01f, -1.01f, -1.01f, 1.0f, 0.0f, 0.0f,       0.0f, 1.0f,
        -1.01f, 1.01f, -1.01f,      0.0f, 1.0f, -0.0f,      0.0f, 0.0f,
        1.01f, 1.01f, -1.01f,       1.0f, 0.0f, -0.0f,      1.0f, 0.0f,
        1.01f, -1.01f, -1.01f,      0.0f, 1.0f,  1.0f,      1.0f, 1.0f,

        // Fill in the back face vertex data.
        -1.01f, -1.01f, 1.01f,      0.0f, 1.0f, 1.0f,       1.0f, 1.0f,
        1.01f, -1.01f, 1.01f,       1.0f, 0.0f, 1.0f,       0.0f, 1.0f,
        1.01f, 1.01f, 1.01f,        1.0f, 0.0f, 1.0f,       0.0f, 0.0f,
        -1.01f, 1.01f, 1.01f,       1.0f, 1.0f, 0.0f,       1.0f, 0.0f,

        // Fill in the top face vertex data.
        -1.01f, 1.01f, -1.01f,      0.0f, 1.0f, 0.0f,       0.0f, 1.0f,
        -1.01f, 1.01f, 1.01f,       1.0f, 0.0f, 1.0f,       0.0f, 0.0f,
        1.01f, 1.01f, 1.01f,        0.0f, 1.0f, 1.0f,       1.0f, 0.0f,
        1.01f, 1.01f, -1.01f,       1.0f, 1.0f, 0.0f,       1.0f, 1.0f,

        // Fill in the bottom face vertex data.
        -1.01f, -1.01f, -1.01f, 1.0f,  1.0f, 0.0f,      1.0f, 1.0f,
        1.01f, -1.01f, -1.01f,      0.0f,  1.0f, 1.0f,      0.0f, 1.0f,
        1.01f, -1.01f, 1.01f,       0.0f,  1.0f, 0.0f,      0.0f, 0.0f,
        -1.01f, -1.01f, 1.01f,      1.0f,  1.0f, 0.0f,      1.0f, 0.0f,

        // Fill in the left face vertex data.
        -1.01f, -1.01f, 1.01f,       1.0f, 1.0f, 0.0f,      0.0f, 1.0f,
        -1.01f, 1.01f, 1.01f,        1.0f, 0.0f, 1.0f,      0.0f, 0.0f,
        -1.01f, 1.01f, -1.01f,       1.0f, 0.0f, 1.0f,      1.0f, 0.0f,
        -1.01f, -1.01f, -1.01f,  1.0f, 1.0f, 0.0f,      1.0f, 1.0f,

        // Fill in the right face vertex data.
        1.01f, -1.01f, -1.01f,      1.0f, 1.0f, 0.0f,       0.0f, 1.0f,
        1.01f, 1.01f, -1.01f,       0.0f, 1.0f, 1.0f,       0.0f, 0.0f,
        1.01f, 1.01f, 1.01f,        1.0f, 0.0f, 1.0f,       1.0f, 0.0f,
        1.01f, -1.01f, 1.01f,       0.0f, 1.0f, 1.0f,       1.0f, 1.0f,
    };

    GLuint indices[] = {
        // front
        0, 1, 2,
        0, 2, 3,
        // top
        4, 5, 6,
        4, 6, 7,
        // back
        8, 9, 10,
        8, 10, 11,
        // bottom
        12, 13, 14,
        12, 14, 15,
        // left
        16, 17, 18,
        16, 18, 19,
        // right
        20, 21, 22,
        20, 22, 23,
    };

    //** VAO **
    // Generate vertex arrow object
    glGenVertexArrays(1, &vao);
    // Bind the Vertex Array Object to openGl context
    glBindVertexArray(vao);//otherwise glVertexAttribPointer

    //** VBO **
    // Then bind and set vertex buffer(s).
    // First paramter is how many buffers we have to create
    glGenBuffers(1, &vbo);

    // bind VBO to binding point, here it is GL_ARRAY_BUFFER
    // there are other binding points
    glBindBuffer(GL_ARRAY_BUFFER, vbo);//bind to context
    glBufferData(GL_ARRAY_BUFFER,
        sizeof(vertices),// GPU need to know how much memory needs to be allocated
        vertices,//copy data to GPU
        GL_STATIC_DRAW);// How to use the buffer - buffer is created and modified once

    //** EBO **
    glGenBuffers(1, &ebo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER,
        sizeof(indices),
        indices,
        GL_STATIC_DRAW);


    // ** Attributes **

    //** Vertex Attribute **
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);

    //** Color Attribute **
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(1);

    //** TexCoord attribute **
    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
    glEnableVertexAttribArray(2);

    // It's always a good thing to unbind any buffer/array to prevent strange bugs
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    //** Load and bind texture 1 
    //--------------------------
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);


    //** loadImage and create texture
    // Load image, create texture and generate mipmaps
    int width, height;
    unsigned char* image = SOIL_load_image("wall.jpg", &width, &height, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image);
    glBindTexture(GL_TEXTURE_2D, 0);


    // ** Load and Bind Texture 2
    //---------------------------
    glGenTextures(1, &texture2);
    glBindTexture(GL_TEXTURE_2D, texture2);


    //** loadImage and create texture
    // Load image, create texture and generate mipmaps
    unsigned char* image2 = SOIL_load_image("awesomeface.png", &width, &height, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image2);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image2);
    glBindTexture(GL_TEXTURE_2D, 0);


    // Set texture wrapping to GL_REPEAT (usually basic wrapping method)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    // Set texture filtering parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

}

void render(){

    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Draw our first triangle
    glUseProgram(program);

    //bind 
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture);
    glUniform1i(glGetUniformLocation(program, "Texture"), 0);

    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, texture2);
    glUniform1i(glGetUniformLocation(program, "Texture2"), 1);

    glBindVertexArray(vao);

    // Draw Elements intead of vertex array 
    glDrawArrays(GL_QUADS, 0, 24);
    //glDrawElements(GL_TRIANGLES, 24, GL_UNSIGNED_INT, 0);
    glBindVertexArray(0);

    glutSwapBuffers();
}

void update(){
    GLfloat cameraSpeed = 0.05f;
    camera->setCameraSpeed(cameraSpeed);

    //currentTime uniform
    GLfloat currentTime = glutGet(GLUT_ELAPSED_TIME);
    currentTime = currentTime / 1000;
    GLint currentTimeLocation = glGetUniformLocation(program, "currentTime");
    glUniform1f(currentTimeLocation, currentTime);

    //transforms
    glm::mat4 transform = glm::mat4(1.0f);
    glm::vec3 vScaleVec = glm::vec3(0.51f, 0.51f, 0.0f);

    glm::mat4 model = glm::mat4(1.0);

    if (keyState[(unsigned char)'w'] == BUTTON_DOWN) {
        camera->moveForward();
        std::cout << "e";
    }
    if (keyState[(unsigned char)'s'] == BUTTON_DOWN) {
        camera->moveBack();
        std::cout << "A";
    }

    camera->Update();

    //glm::mat4 projection = glm::perspective(45.0f, (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);
    glm::mat4 projection = camera->getProjectionMatrix();

    glm::mat4 view = glm::lookAt(camera->getCameraPos(), camera->getCameraPos() + camera->getCameraFront(), camera->getCameraUp());

    //glm::mat4 view = glm::lookAt(glm::vec3(1, 1, 0), glm::vec3(0, 1, 0), glm::vec3(0, 0, 1));

    GLfloat radius = 3.5f;
    GLfloat camX = sin(currentTime) * radius;
    GLfloat camZ = cos(currentTime) * radius;
     
    //glm::mat4 view = glm::lookAt(
    //     glm::vec3(camX, 0.0, camZ),
    //     glm::vec3(0.0, 0.0, 0.0),
    //     glm::vec3(0.0, 1.0, 0.0));

    transform = glm::scale(transform, vScaleVec);
    glm::vec3(0.65f, 0.65f, 0.65f);
    //transform = glm::rotate(transform, 90.0f, glm::vec3(0.0, 0.0, 1.0));
    if (vCurrentPos == vPosDest && Dest1or2 == true )
    {       
        Dest1or2 = false;
    }
    else if (vCurrentPos == vPosTrans && Dest1or2 == false)
    {
        Dest1or2 = true;
    }
    if(Dest1or2)
    vCurrentPos = glm::mix(vCurrentPos, vPosDest, currentTime * 0.01f);
    else 
    vCurrentPos = glm::mix(vCurrentPos, vPosTrans, currentTime*0.01f);
    
    //transform = glm::translate(transform, vCurrentPos);
    //transform = glm::translate(transform, glm::vec3(-0.51f, -0.51f, 0.0f));
    //transform = glm::rotate(transform, ((GLfloat)currentTime / 100) * 90.0f, glm::vec3(0.0f, 0.0f, 1.0f));

    // RTS
    GLuint transformLoc = glGetUniformLocation(program, "transform");
    glUniformMatrix4fv(transformLoc, 1, GL_FALSE, glm::value_ptr(transform));

    GLint modelLoc = glGetUniformLocation(program, "model");
    GLint viewLoc = glGetUniformLocation(program, "view");
    GLint projLoc = glGetUniformLocation(program, "projection");

    // Pass them to the shaders
    glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
    glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(camera->getViewMatrix()));
    glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(camera->getProjectionMatrix()));
    //glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
    //glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));


    glutPostRedisplay();
}

void keyboard(unsigned char key, int x, int y) {
    keyState[key] = BUTTON_DOWN;

    //printf("key pressed: %d \n", key);
}

void keyboard_up(unsigned char key, int x, int y) {
    keyState[key] = BUTTON_UP;
}

int main(int argc, char **argv){

    // init glut
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);

    glutInitWindowPosition(300, 200);
    glutInitWindowSize(800, 600);
    glutCreateWindow("QUAD EBO");

    //init GLEW
    glewInit();

    init();

    //clear
    glClearColor(1.0, 0.0, 0.0, 1.0);//clear red

    // register callbacks
    glutDisplayFunc(render);

    glutKeyboardFunc(keyboard);
    glutKeyboardUpFunc(keyboard_up);

    glutIdleFunc(update);

    glutMainLoop();

    return 0;
}

Fragment Shader:

#version 430 core

in vec3 outColor;
in vec2 TexCoord;

out vec4 color;

uniform sampler2D Texture;
uniform sampler2D Texture2;

uniform float currentTime;

void main()
{
    //vec3 colorTemp = outColor * abs(sin(currentTime));
    //color = vec4(colorTemp, 1.0f) ;
    //color = texture(ourTexture, TexCoord) * vec4(outColor, 1.0f) * abs(sin(currentTime))  ;
    
    color = mix(texture(Texture, TexCoord), texture(Texture2, TexCoord), 0.2) * vec4(outColor, 1.0f) * abs(sin(currentTime));
}

Vertex shader:

#version 430 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 color;
layout (location = 2) in vec2 texCoord;

out vec3 outColor;
out vec2 TexCoord;
 
uniform mat4 transform;
 
uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main(void)
{
    gl_Position = projection * view * model * transform * vec4(position, 1.0);
    outColor = color;
    TexCoord = vec2(texCoord.x, 1.0 - texCoord.y);
}

Answer 1

If I comment out that function, it renders all the vertices as if the z-values were all 0

Well, that's because ... they are:

glm::vec3 vScaleVec = glm::vec3(0.51f, 0.51f, 0.0f);
[...]
transform = glm::scale(transform, vScaleVec);
[...]
gl_Position = projection * view * model * transform * vec4(position, 1.0);

You scale with z=0, which means you move all vertices into the z = 0 plane. So it is already flat after your first transformation step (which also means transform is a singular matrix with the third row and column being all zeros). The additional transform steps you have commented out in the code, as well as all the other matrices applied in the shader, won't change any of that, the object is still a flat plane, no matter what other matrices you pre- or post-multiply to it, they just move that plane around.

I don't know which amount of scaling you want, but scaling by 0 is almost never a good idea, and 1 is the neutral element for scaling operations.

Also, why do you have model and transform as separate matrices in the shader? In 3d computer graphics, the model matrix typically contains all the transformations required for mapping the object from it's own local model space to the world space. Even if you need to track separate parts of the transformation internally, you typically don't need these during actual rendering on the gpu, and should multiply all of these together on the CPU, and just send the accumulated transformation as the model matrix to the shader.