skein/src/gfx.cpp

#include "gfx.hpp"

#include <iostream>

#include "glm/glm.hpp"
#include "glm/gtc/matrix_transform.hpp"

#include "io.hpp"

float aspect_;

// Initialize GLFW, OpenGL and GLEW, open a window and make it the current context.
// Returns 0 for success, and -1 for any failure.
// Failures are printed to STDERR.
int initGraphics(GLFWwindow** window, const std::string& title)
{
    // Set up GLFW, OpenGL and GLEW.
    if (!glfwInit())
    {
        std::cerr << "Failed to initialize GLFW" << std::endl;
        return -1;
    }
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GLFW_TRUE);

    *window = glfwCreateWindow(640, 480, title.c_str(), NULL, NULL);

    if (!window)
    {
        glfwTerminate();
        std::cerr << "Failed to open window with GLFW" << std::endl;
        return -1;
    }

    glfwSetWindowSizeCallback(*window, windowSizeCallback);

    glfwMakeContextCurrent(*window);

    glewExperimental = GL_TRUE;
    if (glewInit() != GLEW_OK)
    {
        std::cerr << "Failed to initialize GLEW" << std::endl;
        return -1;
    }

    glEnable(GL_DEPTH_TEST);

    return 0;
}

void windowSizeCallback(GLFWwindow* window, int width, int height)
{
    aspect_ = (float)width / (float)height;
    glViewport(0, 0, width, height);
}

GLuint compileShader(const std::string& shaderPath, GLenum shaderType)
{
    GLuint shader;
    GLint success;

    std::string shaderSource = readFile(shaderPath);
    const char* source = shaderSource.c_str();

    shader = glCreateShader(shaderType);
    glShaderSource(shader, 1, &source, NULL);
    glCompileShader(shader);

    glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
    if (!success)
    {
        GLchar infoLog[512];
        glGetShaderInfoLog(shader, 512, NULL, infoLog);
        std::cerr << "shader compilation failed" << std::endl
            << infoLog << std::endl;
    }

    return shader;
}

GLuint compileShaderProgram(const std::string& fragShaderPath)
{
    GLuint vertShader = compileShader("./vert.glsl", GL_VERTEX_SHADER);
    GLuint fragShader = compileShader(fragShaderPath, GL_FRAGMENT_SHADER);

    GLuint shaderProgram = glCreateProgram();
    glAttachShader(shaderProgram, vertShader);
    glAttachShader(shaderProgram, fragShader);
    glLinkProgram(shaderProgram);

    GLint success;
    GLchar infoLog[512];
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if (!success)
    {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cerr << "shader linking failed" << std::endl
            << infoLog << std::endl;
        exit(-1);
    }

    // We no longer need the individual shaders
    glDeleteShader(vertShader);
    glDeleteShader(fragShader);

    return shaderProgram;
}

void updateProjectionMatrix(GLuint shaderProgram)
{
    float left = -aspect_, right = aspect_, bottom = -1.0, top = 1.0, near = -2.0, far = 1.0;
    glm::mat4 projection = glm::ortho(left, right, bottom, top, near, far);
    GLint projectionLocation = getShaderUniformLocation(shaderProgram, "_Projection");
    glUniformMatrix4fv(projectionLocation, 1, GL_FALSE, &projection[0][0]);
}

void updateModelMatrix(GLuint shaderProgram)
{
    glm::mat4 model = glm::mat4(1.0);
    GLint modelLocation = getShaderUniformLocation(shaderProgram, "_Model");
    glUniformMatrix4fv(modelLocation, 1, GL_FALSE, &model[0][0]);
}

void updateViewMatrix(GLuint shaderProgram, float time)
{
    glm::mat4 view = glm::mat4(1.0);

    // Rotation
    constexpr float angle = glm::radians(10.0);
    glm::vec3 axis = glm::vec3(0.0, 1.0, 0.0);
    view = glm::rotate(view, angle * time, axis);

    GLint viewLocation = getShaderUniformLocation(shaderProgram, "_View");
    glUniformMatrix4fv(viewLocation, 1, GL_FALSE, &view[0][0]);
}

void updateModelViewProjectionMatrix(GLuint shaderProgram, float time)
{
    // Calculate matrices
    updateProjectionMatrix(shaderProgram);
    updateModelMatrix(shaderProgram);
    updateViewMatrix(shaderProgram, time);
}

GLint getShaderUniformLocation(GLuint shaderProgram, const std::string& uniformName)
{
    GLint location = glGetUniformLocation(shaderProgram, uniformName.c_str());
    if (location == -1)
    {
        std::cerr << "Could not find uniform: " << uniformName << std::endl;
        return -1;
    }

    return location;
}