c2_triangle_uniform.cc

// Link statically with GLEW
#define GLEW_STATIC

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

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

int main()
{
    auto t_start = std::chrono::high_resolution_clock::now();

    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[] = {
         0.0f,  0.5f,
         0.5f, -0.5f,
        -0.5f, -0.5f
    };

    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, 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, 0, 0);

    // Get the location of the color uniform
    GLint uniColor = glGetUniformLocation(shaderProgram, "triangleColor");

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

        // Set the color of the triangle
        auto t_now = std::chrono::high_resolution_clock::now();
        float time = std::chrono::duration_cast<std::chrono::duration<float>>(t_now - t_start).count();
        
        glUniform3f(uniColor, (sin(time * 4.0f) + 1.0f) / 2.0f, 0.0f, 0.0f);

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

        // Draw a triangle from the 3 vertices
        glDrawArrays(GL_TRIANGLES, 0, 3);

        // Swap buffers
        window.display();
    }

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

    glDeleteBuffers(1, &vbo);

    glDeleteVertexArrays(1, &vao);

    window.close();

    return 0;
}