opengl.cpp

// Link statically with GLEW
#define GLEW_STATIC

// Headers
#include <GL/glew.h>
#include <SOIL.h>
#include <SFML/Window.hpp>

// Shader sources
const GLchar* vertexSource = R"glsl(
    #version 150 core
    in vec2 position;
    in vec3 color;
    in vec2 texcoord;
    out vec3 Color;
    out vec2 Texcoord;
    void main()
    {
        Color = color;
        Texcoord = texcoord;
        gl_Position = vec4(position, 0.0, 1.0);
    }
)glsl";
const GLchar* fragmentSource = R"glsl(
    #version 150 core
    in vec3 Color;
    in vec2 Texcoord;
    out vec4 outColor;
    uniform sampler2D tex;
    void main()
    {
        outColor = texture(tex, Texcoord) * vec4(Color, 1.0);
    }
)glsl";

int main()
{
    sf::ContextSettings settings;
    settings.depthBits = 24;
    settings.stencilBits = 8;

    sf::Window window(sf::VideoMode(800, 600, 32), "OpenGL", sf::Style::Titlebar | sf::Style::Close, settings);

    // Initialize GLEW
    glewExperimental = GL_TRUE;
    glewInit();

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

    // Create a Vertex Buffer Object and copy the vertex data to it
    GLuint vbo;
    glGenBuffers(1, &vbo);

    GLfloat vertices[] = {
    //  Position      Color             Texcoords
        -0.5f,  0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, // Top-left
         0.5f,  0.5f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, // Top-right
         0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, // Bottom-right
        -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f  // Bottom-left
    };

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

    // Create an element array
    GLuint ebo;
    glGenBuffers(1, &ebo);

    GLuint elements[] = {
        0, 1, 2,
        2, 3, 0
    };

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW);

    // Create and compile the vertex shader
    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexSource, NULL);
    glCompileShader(vertexShader);

    // Create and compile the fragment shader
    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
    glCompileShader(fragmentShader);

    // Link the vertex and fragment shader into a shader program
    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glBindFragDataLocation(shaderProgram, 0, "outColor");
    glLinkProgram(shaderProgram);
    glUseProgram(shaderProgram);

    // Specify the layout of the vertex data
    GLint posAttrib = glGetAttribLocation(shaderProgram, "position");
    glEnableVertexAttribArray(posAttrib);
    glVertexAttribPointer(posAttrib, 2, GL_FLOAT, GL_FALSE, 7 * sizeof(GLfloat), 0);

    GLint colAttrib = glGetAttribLocation(shaderProgram, "color");
    glEnableVertexAttribArray(colAttrib);
    glVertexAttribPointer(colAttrib, 3, GL_FLOAT, GL_FALSE, 7 * sizeof(GLfloat), (void*)(2 * sizeof(GLfloat)));

    GLint texAttrib = glGetAttribLocation(shaderProgram, "texcoord");
    glEnableVertexAttribArray(texAttrib);
    glVertexAttribPointer(texAttrib, 2, GL_FLOAT, GL_FALSE, 7 * sizeof(GLfloat), (void*)(5 * sizeof(GLfloat)));

    // Load texture
    GLuint tex;
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);

    int width, height;
    unsigned char* image = SOIL_load_image("sample.png", &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);

    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);

    bool running = true;
    while (running)
    {
        sf::Event windowEvent;
        while (window.pollEvent(windowEvent))
        {
            switch (windowEvent.type)
            {
            case sf::Event::Closed:
                running = false;
                break;
            }
        }

        // Clear the screen to black
        glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // Draw a rectangle from the 2 triangles using 6 indices
        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

        // Swap buffers
        window.display();
    }

    glDeleteTextures(1, &tex);

    glDeleteProgram(shaderProgram);
    glDeleteShader(fragmentShader);
    glDeleteShader(vertexShader);

    glDeleteBuffers(1, &ebo);
    glDeleteBuffers(1, &vbo);

    glDeleteVertexArrays(1, &vao);

    window.close();

    return 0;
}