OpenGL mixing two textures always picks up the first texture

Question

Here is my code where I mix two texture,

main.cpp

#include <iostream>

// GLEW
#include <GL/glew.h>

// GLFW
#include <GLFW/glfw3.h>


// Shader Class
#include "Shader.h"

// SOIL2 JSpartan
#include "SOIL2.h"

const int WIDTH=500, HEIGHT=600;

int main() {

    // Init GLFW
    glfwInit( );

    // Set all the required options for 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 );

    glfwWindowHint( GLFW_RESIZABLE, GL_FALSE );

    // Create a GLFWwindow object that we can use for GLFW's functions
    GLFWwindow *window = glfwCreateWindow( WIDTH, HEIGHT, "LearnOpenGL", nullptr, nullptr );

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

    if ( nullptr == window )
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate( );

        return EXIT_FAILURE;
    }

    glfwMakeContextCurrent( window );

    // Set this to true so GLEW knows to use a modern approach to retrieving function pointers and extensions
    glewExperimental = GL_TRUE;
    // Initialize GLEW to setup the OpenGL Function pointers
    if ( GLEW_OK != glewInit( ) )
    {
        std::cout << "Failed to initialize GLEW" << std::endl;
        return EXIT_FAILURE;
    }

    // Define the viewport dimensions
    glViewport( 0, 0, screenWidth, screenHeight );
    // enable alpha support
    glEnable( GL_BLEND );
    glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );


    // load shaders
    Shader *ourShader = new Shader("res/shaders/core.vs","res/shaders/core.fs");

    GLfloat vertices[] = {
        1.0f, 1.0f, 0.0f,       1.0f, 0.0f, 0.0f,       1.0f, 1.0f, // top right corner
        1.0f, -1.0f, 0.0f,      0.0f, 1.0f, 0.0f,       1.0f, 0.0f, // bottom right corner
        -1.0f, -1.0f, 0.0f,     0.0f, 0.0f, 1.0f,       0.0f, 0.0f, // bottom left corner
        -1.0f, 1.0f, 0.0f,      1.0f, 1.0f, 0.0f,       0.0f, 1.0f  // top left corner
    };

    GLuint indices[] = {
        0, 1, 2, // trainagle 1 right sided
        2, 3, 0
    };

    GLuint VAO, VBO, EBO;

    glGenVertexArrays( 1, &VAO );
    glBindVertexArray( VAO );

    glGenBuffers( 1, &VBO );
    glBindBuffer( GL_ARRAY_BUFFER, VBO );
    glBufferData( GL_ARRAY_BUFFER, sizeof( vertices ), vertices, GL_STATIC_DRAW );

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


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

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

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


    // Load textures
    GLuint textures[2];
    glGenTextures(2, textures);

    int width, height;
    unsigned char* image;

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textures[0]);
    image = SOIL_load_image("res/face1.jpg", &width, &height, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    SOIL_free_image_data(image);
    glUniform1i(glGetUniformLocation(ourShader->Program, "face1"), 0);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, textures[1]);
    image = SOIL_load_image("res/face2.jpg", &width, &height, 0, SOIL_LOAD_RGB);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, image);
    SOIL_free_image_data(image);
    glUniform1i(glGetUniformLocation(ourShader->Program, "face2"), 1);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    //glBindVertexArray(0);



    // Game loop
    while ( !glfwWindowShouldClose( window ) )
    {
        // Check if any events have been activiated (key pressed, mouse moved etc.) and call corresponding response functions
        glfwPollEvents( );


        glClearColor(0.2f, 0.3f, 0.5f, 1.0f);
        glClear( GL_COLOR_BUFFER_BIT );
        ourShader->Use();

        //glBindVertexArray(VAO);

        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        //glDrawArrays( GL_TRIANGLES, 0, 3 );


        // Swap the screen buffers
        glfwSwapBuffers( window );
    }

}

Here is my vertex shader:

#version 330 core

layout (location = 0) in vec3 position;
layout (location = 1) in vec3 color;
layout (location = 2) in vec2 texCoord;


out vec3 ourColor;
out vec2 TexCoord;

void main() {
    ourColor = color;
    TexCoord = vec2(texCoord.x, 1-texCoord.y);
    gl_Position = vec4(position.x, position.y, position.z, 1.0);
}

And this is the fragment shader,

#version 330 core
in vec3 ourColor;
in vec2 TexCoord;

out vec4 color;
uniform sampler2D face1;
uniform sampler2D face2;


void main() {
    vec4 colorFace1 = texture(face1, TexCoord);
    vec4 colorFace2 = texture(face2, TexCoord);

    color = colorFace2; //* vec4(ourColor, 1.0);;//vec4(ourColor, 1.0f);
}

Now the problem is that the whenever I run the code, the code runs and the output is always "face1.jpg". I have followed the step by step instructions as mentioned here .

If you visit the website in the link above the output of the program must be mixing of two images as shown in this post.

Answer 1

In your code is an issue with the order of the instructions, because glUniform specifies the value of a uniform variable for the current program object.

The uniform location can be retrieved at any time by glGetUniformLocation , and stored for later use, after the program is linked successfully ( glLinkProgram ):

int texLocationFace1 = glGetUniformLocation(ourShader->Program, "face1");
int texLocationFace2 = glGetUniformLocation(ourShader->Program, "face2");

But to set the value of a uniform variable, the program has to be the active program ( glUseProgram ). Note, there is no parameter to select the program, in the sinature of glUniform .
You have to use the program,

ourShader->Use();

before you set the values of the uniforms:

glUniform1i(texLocationFace1, 0);
glUniform1i(texLocationFace2, 1);

Note, you never set the texture sampler uniforms, because you call glUniform , before any shader program is used. The uniform variables face and face 2 by default are initialized with 0. Therefore, the output is always "face1.jpg" because this texture is bound to texture unit GL_TEXTURE0 .

Since you only use one shader program and you don't change it, it is sufficient to use the program and to set the uniforms before the main loop:

ourShader->Use();
glUniform1i(texLocationFace1, 0);
glUniform1i(texLocationFace2, 1);

while ( !glfwWindowShouldClose( window ) )
{
    ....
}

Answer 2

You are not mixing any colors in your fragment shader. You are making a texture lookup from both face1 and face2 and then you only return the latter and discard the former. Try

color = 0.5 * (colorFace1 + colorFace2); 

in your fragment shader.

If what you are seeing is really face1 and not face2, then there is something wrong that I didn't spot somewhere else, as well.