tomdalling.com OpenGL article 2 modified to use two textures

fragment-shader.txt

#version 150

uniform sampler2D tex;
uniform sampler2D tex2;

in vec2 fragTexCoord;

out vec4 finalColor;

void main() {
    vec4 color1 = texture(tex, fragTexCoord);
    vec4 color2 = texture(tex2, fragTexCoord);
    finalColor = 0.5*color1 + 0.5*color2;
}

main.cpp

/*
 main

 Copyright 2012 Thomas Dalling - http://tomdalling.com/

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
 */

#include "platform.hpp"

// third-party libraries
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>

// standard C++ libraries
#include <cassert>
#include <iostream>
#include <stdexcept>
#include <cmath>

// tdogl classes
#include "tdogl/Program.h"
#include "tdogl/Texture.h"

// constants
const glm::vec2 SCREEN_SIZE(800, 600);

// globals
GLFWwindow* gWindow = NULL;
tdogl::Texture* gTexture = NULL;
tdogl::Texture* gTexture2 = NULL;
tdogl::Program* gProgram = NULL;
GLuint gVAO = 0;
GLuint gVBO = 0;


// loads the vertex shader and fragment shader, and links them to make the global gProgram
static void LoadShaders() {
    std::vector<tdogl::Shader> shaders;
    shaders.push_back(tdogl::Shader::shaderFromFile(ResourcePath("vertex-shader.txt"), GL_VERTEX_SHADER));
    shaders.push_back(tdogl::Shader::shaderFromFile(ResourcePath("fragment-shader.txt"), GL_FRAGMENT_SHADER));
    gProgram = new tdogl::Program(shaders);
}


// loads a triangle into the VAO global
static void LoadTriangle() {
    // make and bind the VAO
    glGenVertexArrays(1, &gVAO);
    glBindVertexArray(gVAO);
    
    // make and bind the VBO
    glGenBuffers(1, &gVBO);
    glBindBuffer(GL_ARRAY_BUFFER, gVBO);
    
    // Put the three triangle vertices (XYZ) and texture coordinates (UV) into the VBO
    GLfloat vertexData[] = {
        //  X     Y     Z       U     V
         0.0f, 0.8f, 0.0f,   0.5f, 1.0f,
        -0.8f,-0.8f, 0.0f,   0.0f, 0.0f,
         0.8f,-0.8f, 0.0f,   1.0f, 0.0f,
    };
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertexData), vertexData, GL_STATIC_DRAW);

    // connect the xyz to the "vert" attribute of the vertex shader
    glEnableVertexAttribArray(gProgram->attrib("vert"));
    glVertexAttribPointer(gProgram->attrib("vert"), 3, GL_FLOAT, GL_FALSE, 5*sizeof(GLfloat), NULL);
        
    // connect the uv coords to the "vertTexCoord" attribute of the vertex shader
    glEnableVertexAttribArray(gProgram->attrib("vertTexCoord"));
    glVertexAttribPointer(gProgram->attrib("vertTexCoord"), 2, GL_FLOAT, GL_TRUE,  5*sizeof(GLfloat), (const GLvoid*)(3 * sizeof(GLfloat)));

    // unbind the VAO
    glBindVertexArray(0);
}


// loads the file "hazard.png" into gTexture
static void LoadTexture() {
    tdogl::Bitmap bmp = tdogl::Bitmap::bitmapFromFile(ResourcePath("hazard.png"));
    bmp.flipVertically();
    gTexture = new tdogl::Texture(bmp);

    tdogl::Bitmap bmp2 = tdogl::Bitmap::bitmapFromFile(ResourcePath("hazard2.png"));
    bmp2.flipVertically();
    gTexture2 = new tdogl::Texture(bmp2);
}


// draws a single frame
static void Render() {
    // clear everything
    glClearColor(0, 0, 0, 1); // black
    glClear(GL_COLOR_BUFFER_BIT);
    
    // bind the program (the shaders)
    gProgram->use();
        
    // bind the texture and set the "tex" uniform in the fragment shader
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, gTexture->object());
    gProgram->setUniform("tex", 0); //set to 0 because the texture is bound to GL_TEXTURE0

    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, gTexture2->object());
    gProgram->setUniform("tex2", 1); //set to 0 because the texture is bound to GL_TEXTURE0

    // bind the VAO (the triangle)
    glBindVertexArray(gVAO);
    
    // draw the VAO
    glDrawArrays(GL_TRIANGLES, 0, 3);
    
    // unbind the VAO, the program and the texture
    glBindVertexArray(0);
    glBindTexture(GL_TEXTURE_2D, 0);
    gProgram->stopUsing();
    
    // swap the display buffers (displays what was just drawn)
    glfwSwapBuffers(gWindow);
}

void OnError(int errorCode, const char* msg) {
    throw std::runtime_error(msg);
}

// the program starts here
void AppMain() {
    // initialise GLFW
    glfwSetErrorCallback(OnError);
    if(!glfwInit())
        throw std::runtime_error("glfwInit failed");
    
    // open a window with GLFW
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
    gWindow = glfwCreateWindow((int)SCREEN_SIZE.x, (int)SCREEN_SIZE.y, "OpenGL Tutorial", NULL, NULL);
    if(!gWindow)
        throw std::runtime_error("glfwCreateWindow failed. Can your hardware handle OpenGL 3.2?");

    // GLFW settings
    glfwMakeContextCurrent(gWindow);
    
    // initialise GLEW
    glewExperimental = GL_TRUE; //stops glew crashing on OSX :-/
    if(glewInit() != GLEW_OK)
        throw std::runtime_error("glewInit failed");

    // print out some info about the graphics drivers
    std::cout << "OpenGL version: " << glGetString(GL_VERSION) << std::endl;
    std::cout << "GLSL version: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << std::endl;
    std::cout << "Vendor: " << glGetString(GL_VENDOR) << std::endl;
    std::cout << "Renderer: " << glGetString(GL_RENDERER) << std::endl;

    // make sure OpenGL version 3.2 API is available
    if(!GLEW_VERSION_3_2)
        throw std::runtime_error("OpenGL 3.2 API is not available.");

    // OpenGL settings
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    // load vertex and fragment shaders into opengl
    LoadShaders();

    // load the texture
    LoadTexture();

    // create buffer and fill it with the points of the triangle
    LoadTriangle();

    // run while the window is open
    while(!glfwWindowShouldClose(gWindow)){
        // process pending events
        glfwPollEvents();
        
        // draw one frame
        Render();
    }

    // clean up and exit
    glfwTerminate();
}


int main(int argc, char *argv[]) {
    try {
        AppMain();
    } catch (const std::exception& e){
        std::cerr << "ERROR: " << e.what() << std::endl;
        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}