How do I swap images using OpenGL and Obj-C ?

OpenGL OpenGL: Basic Coding
1

I’m very new to open GL and recently have been following ModernOpenGL Tutorial about shader and texture here.

The tutorial is using C++, and now I need to use Obj-C which I never use before and I’m having difficulty. So, I want to switch 2 images in a certain time (fps). So far, I can change 2 colors at a certain frequency using this [UPDATED]


#include <iostream>
#define  GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include "SOIL2/SOIL2.h"
#include "Shader.h"

using namespace std;

//window
const GLuint WIDTH = 700, HEIGHT = 700;
int main( )
{
    glfwInit( );

    //GLFW
    glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3 );
    glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
    glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE );
    glfwWindowHint( GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE ); //only for mac
    glfwWindowHint( GLFW_RESIZABLE, GL_FALSE );

    GLFWwindow *window = glfwCreateWindow( WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr );

    int screenWidth, screenHeight;
    glfwGetFramebufferSize( window, &screenWidth, &screenHeight );

    if ( nullptr == window )
    {
        cout << "Failed to create GLFW window" << endl;
        glfwTerminate( );
        return EXIT_FAILURE;
    }

    glfwMakeContextCurrent( window );

    //ModernOpenGL
    glewExperimental = GL_TRUE;

    if ( GLEW_OK != glewInit( ) )
    {
        cout << "Failed to initialize GLEW" << endl;
        return EXIT_FAILURE;
    }

    //viewport
    glViewport( 0, 0, screenWidth, screenHeight );

    //enable alpha
    glEnable( GL_BLEND );
    glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );

    //shaders
    Shader ourShader( "resources/shaders/core.vs", "resources/shaders/core.frag" );

    //vertices
    GLfloat vertices[] =
    {
        //position            //color              //texture Coords
        1.0f,  1.0f, 0.0f,    1.0f, 0.0f, 0.0f,    1.0f, 1.0f, // Top Right
        1.0f, -1.0f, 0.0f,    0.0f, 1.0f, 0.0f,    1.0f, 0.0f, // Bottom Right
        -1.0f, -1.0f, 0.0f,   0.0f, 0.0f, 1.0f,    0.0f, 0.0f, // Bottom Left
        -1.0f,  1.0f, 0.0f,   1.0f, 1.0f, 0.0f,    0.0f, 1.0f  // Top Left
    };

    GLuint indices[] =
    {
      0, 1, 3, // 1st triangle
      1, 2, 3  // 2nd triangle
    };

    GLuint VBO, VAO, EBO;
    glGenVertexArrays( 1, &VAO );
    glGenBuffers( 1, &VBO );
    glGenBuffers( 1, &EBO );

    glBindVertexArray( VAO );

    glBindBuffer( GL_ARRAY_BUFFER, VBO );
    glBufferData( GL_ARRAY_BUFFER, sizeof( vertices ), vertices, GL_STATIC_DRAW );

    glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, EBO );
    glBufferData( GL_ELEMENT_ARRAY_BUFFER, sizeof( indices ), indices, GL_STATIC_DRAW );

    //position
    glVertexAttribPointer( 0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof( GLfloat ), ( GLvoid * ) 0 );
    glEnableVertexAttribArray(0);
    //color
    glVertexAttribPointer( 1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof( GLfloat ), ( GLvoid * )( 3 * sizeof( GLfloat ) ) );
    glEnableVertexAttribArray(1);
    //texture Coord
    glVertexAttribPointer( 2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof( GLfloat ), ( GLvoid * )( 6 * sizeof( GLfloat ) ) );
    glEnableVertexAttribArray( 2 );

    glBindVertexArray( 0 ); // unbind VAO

    //create texture
    GLuint textures[2];
    int width, height;
    unsigned char * image;

    glGenTextures(2, textures);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textures[0]);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textures[1]);

    //parameters
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );
    //filtering
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textures[0]);
    image = SOIL_load_image("resources/res/images/green.png", &width, &height, 0, SOIL_LOAD_RGBA);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);
    SOIL_free_image_data(image);
    glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture1"), 0);

     glActiveTexture(GL_TEXTURE0);
     glBindTexture(GL_TEXTURE_2D, textures[1]);
     image = SOIL_load_image("resources/res/images/red.png", &width, &height, 0, SOIL_LOAD_RGBA);
     glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);
     SOIL_free_image_data(image);
     glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture2"), 1);

    //game loop
    while ( !glfwWindowShouldClose( window ) )
    {
        glfwPollEvents( );

        //draw container
        glBindVertexArray( VAO );
        glDrawElements( GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0 );
        glBindVertexArray( 0 );

        glfwSwapBuffers( window );
    }

    //de-alocated stuff
    glDeleteVertexArrays( 1, &VAO );
    glDeleteBuffers( 1, &VBO );
    glDeleteBuffers( 1, &EBO );

    glfwTerminate( );
    return EXIT_SUCCESS;
}

And here’s the texture frag

#version 330 core 
in vec3 ourColor; 
in vec2 TexCoord;  
out vec4 color;  
uniform sampler2D ourTexture1; 
uniform sampler2D ourTexture2; 
uniform int usetexture = 0; 
void main() { 
     if (usetexture == 0) color = texture(ourTexture1, TexCoord); 
     if (usetexture == 1) color = texture(ourTexture1, TexCoord); }

I want to change between img1 and img2 from SOIL load image. But has been stuck. Any advice ?