//========================================================================
// This is an example program for the GLFW library
//
// The program uses a "split window" view, rendering four views of the
// same scene in one window (e.g. uesful for 3D modelling software). This
// demo uses scissors to separete the four different rendering areas from
// each other.
//
// (If the code seems a little bit strange here and there, it may be
//  because I am not a friend of orthogonal projections)
//========================================================================

#define GLFW_INCLUDE_GLU
#include <GL/glfw3.h>

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif


//========================================================================
// Global variables
//========================================================================

// Mouse position
static int xpos = 0, ypos = 0;

// Window size
static int width, height;

// Active view: 0 = none, 1 = upper left, 2 = upper right, 3 = lower left,
// 4 = lower right
static int active_view = 0;

// Rotation around each axis
static int rot_x = 0, rot_y = 0, rot_z = 0;

// Do redraw?
static int do_redraw = 1;


//========================================================================
// Draw a solid torus (use a display list for the model)
//========================================================================

#define TORUS_MAJOR     1.5
#define TORUS_MINOR     0.5
#define TORUS_MAJOR_RES 32
#define TORUS_MINOR_RES 32

static void drawTorus(void)
{
    static GLuint torus_list = 0;
    int    i, j, k;
    double s, t, x, y, z, nx, ny, nz, scale, twopi;

    if (!torus_list)
    {
        // Start recording displaylist
        torus_list = glGenLists(1);
        glNewList(torus_list, GL_COMPILE_AND_EXECUTE);

        // Draw torus
        twopi = 2.0 * M_PI;
        for (i = 0;  i < TORUS_MINOR_RES;  i++)
        {
            glBegin(GL_QUAD_STRIP);
            for (j = 0;  j <= TORUS_MAJOR_RES;  j++)
            {
                for (k = 1;  k >= 0;  k--)
                {
                    s = (i + k) % TORUS_MINOR_RES + 0.5;
                    t = j % TORUS_MAJOR_RES;

                    // Calculate point on surface
                    x = (TORUS_MAJOR + TORUS_MINOR * cos(s * twopi / TORUS_MINOR_RES)) * cos(t * twopi / TORUS_MAJOR_RES);
                    y = TORUS_MINOR * sin(s * twopi / TORUS_MINOR_RES);
                    z = (TORUS_MAJOR + TORUS_MINOR * cos(s * twopi / TORUS_MINOR_RES)) * sin(t * twopi / TORUS_MAJOR_RES);

                    // Calculate surface normal
                    nx = x - TORUS_MAJOR * cos(t * twopi / TORUS_MAJOR_RES);
                    ny = y;
                    nz = z - TORUS_MAJOR * sin(t * twopi / TORUS_MAJOR_RES);
                    scale = 1.0 / sqrt(nx*nx + ny*ny + nz*nz);
                    nx *= scale;
                    ny *= scale;
                    nz *= scale;

                    glNormal3f((float) nx, (float) ny, (float) nz);
                    glVertex3f((float) x, (float) y, (float) z);
                }
            }

            glEnd();
        }

        // Stop recording displaylist
        glEndList();
    }
    else
    {
        // Playback displaylist
        glCallList(torus_list);
    }
}


//========================================================================
// Draw the scene (a rotating torus)
//========================================================================

static void drawScene(void)
{
    const GLfloat model_diffuse[4]  = {1.0f, 0.8f, 0.8f, 1.0f};
    const GLfloat model_specular[4] = {0.6f, 0.6f, 0.6f, 1.0f};
    const GLfloat model_shininess   = 20.0f;

    glPushMatrix();

    // Rotate the object
    glRotatef((GLfloat) rot_x * 0.5f, 1.0f, 0.0f, 0.0f);
    glRotatef((GLfloat) rot_y * 0.5f, 0.0f, 1.0f, 0.0f);
    glRotatef((GLfloat) rot_z * 0.5f, 0.0f, 0.0f, 1.0f);

    // Set model color (used for orthogonal views, lighting disabled)
    glColor4fv(model_diffuse);

    // Set model material (used for perspective view, lighting enabled)
    glMaterialfv(GL_FRONT, GL_DIFFUSE, model_diffuse);
    glMaterialfv(GL_FRONT, GL_SPECULAR, model_specular);
    glMaterialf(GL_FRONT, GL_SHININESS, model_shininess);

    // Draw torus
    drawTorus();

    glPopMatrix();
}


//========================================================================
// Draw a 2D grid (used for orthogonal views)
//========================================================================

static void drawGrid(float scale, int steps)
{
    int i;
    float x, y;

    glPushMatrix();

    // Set background to some dark bluish grey
    glClearColor(0.05f, 0.05f, 0.2f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    // Setup modelview matrix (flat XY view)
    glLoadIdentity();
    gluLookAt(0.0, 0.0, 1.0,
              0.0, 0.0, 0.0,
              0.0, 1.0, 0.0);

    // We don't want to update the Z-buffer
    glDepthMask(GL_FALSE);

    // Set grid color
    glColor3f(0.0f, 0.5f, 0.5f);

    glBegin(GL_LINES);

    // Horizontal lines
    x = scale * 0.5f * (float) (steps - 1);
    y = -scale * 0.5f * (float) (steps - 1);
    for (i = 0;  i < steps;  i++)
    {
        glVertex3f(-x, y, 0.0f);
        glVertex3f(x, y, 0.0f);
        y += scale;
    }

    // Vertical lines
    x = -scale * 0.5f * (float) (steps - 1);
    y = scale * 0.5f * (float) (steps - 1);
    for (i = 0;  i < steps;  i++)
    {
        glVertex3f(x, -y, 0.0f);
        glVertex3f(x, y, 0.0f);
        x += scale;
    }

    glEnd();

    // Enable Z-buffer writing again
    glDepthMask(GL_TRUE);

    glPopMatrix();
}


//========================================================================
// Draw all views
//========================================================================

static void drawAllViews(void)
{
    const GLfloat light_position[4] = {0.0f, 8.0f, 8.0f, 1.0f};
    const GLfloat light_diffuse[4]  = {1.0f, 1.0f, 1.0f, 1.0f};
    const GLfloat light_specular[4] = {1.0f, 1.0f, 1.0f, 1.0f};
    const GLfloat light_ambient[4]  = {0.2f, 0.2f, 0.3f, 1.0f};
    double aspect;

    // Calculate aspect of window
    if (height > 0)
        aspect = (double) width / (double) height;
    else
        aspect = 1.0;

    // Clear screen
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Enable scissor test
    glEnable(GL_SCISSOR_TEST);

    // Enable depth test
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);

    // ** ORTHOGONAL VIEWS **

    // For orthogonal views, use wireframe rendering
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

    // Enable line anti-aliasing
    glEnable(GL_LINE_SMOOTH);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    // Setup orthogonal projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-3.0 * aspect, 3.0 * aspect, -3.0, 3.0, 1.0, 50.0);

    // Upper left view (TOP VIEW)
    glViewport(0, height / 2, width / 2, height / 2);
    glScissor(0, height / 2, width / 2, height / 2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0.0f, 10.0f, 1e-3f,   // Eye-position (above)
              0.0f, 0.0f, 0.0f,     // View-point
              0.0f, 1.0f, 0.0f);   // Up-vector
    drawGrid(0.5, 12);
    drawScene();

    // Lower left view (FRONT VIEW)
    glViewport(0, 0, width / 2, height / 2);
    glScissor(0, 0, width / 2, height / 2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0.0f, 0.0f, 10.0f,    // Eye-position (in front of)
              0.0f, 0.0f, 0.0f,     // View-point
              0.0f, 1.0f, 0.0f);   // Up-vector
    drawGrid(0.5, 12);
    drawScene();

    // Lower right view (SIDE VIEW)
    glViewport(width / 2, 0, width / 2, height / 2);
    glScissor(width / 2, 0, width / 2, height / 2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(10.0f, 0.0f, 0.0f,    // Eye-position (to the right)
              0.0f, 0.0f, 0.0f,     // View-point
              0.0f, 1.0f, 0.0f);   // Up-vector
    drawGrid(0.5, 12);
    drawScene();

    // Disable line anti-aliasing
    glDisable(GL_LINE_SMOOTH);
    glDisable(GL_BLEND);

    // ** PERSPECTIVE VIEW **

    // For perspective view, use solid rendering
    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

    // Enable face culling (faster rendering)
    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    glFrontFace(GL_CW);

    // Setup perspective projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(65.0f, aspect, 1.0f, 50.0f);

    // Upper right view (PERSPECTIVE VIEW)
    glViewport(width / 2, height / 2, width / 2, height / 2);
    glScissor(width / 2, height / 2, width / 2, height / 2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(3.0f, 1.5f, 3.0f,     // Eye-position
              0.0f, 0.0f, 0.0f,     // View-point
              0.0f, 1.0f, 0.0f);   // Up-vector

    // Configure and enable light source 1
    glLightfv(GL_LIGHT1, GL_POSITION, light_position);
    glLightfv(GL_LIGHT1, GL_AMBIENT, light_ambient);
    glLightfv(GL_LIGHT1, GL_DIFFUSE, light_diffuse);
    glLightfv(GL_LIGHT1, GL_SPECULAR, light_specular);
    glEnable(GL_LIGHT1);
    glEnable(GL_LIGHTING);

    // Draw scene
    drawScene();

    // Disable lighting
    glDisable(GL_LIGHTING);

    // Disable face culling
    glDisable(GL_CULL_FACE);

    // Disable depth test
    glDisable(GL_DEPTH_TEST);

    // Disable scissor test
    glDisable(GL_SCISSOR_TEST);

    // Draw a border around the active view
    if (active_view > 0 && active_view != 2)
    {
        glViewport(0, 0, width, height);

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0.0, 2.0, 0.0, 2.0, 0.0, 1.0);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        glTranslatef((GLfloat) ((active_view - 1) & 1), (GLfloat) (1 - (active_view - 1) / 2), 0.0f);

        glColor3f(1.0f, 1.0f, 0.6f);

        glBegin(GL_LINE_STRIP);
        glVertex2i(0, 0);
        glVertex2i(1, 0);
        glVertex2i(1, 1);
        glVertex2i(0, 1);
        glVertex2i(0, 0);
        glEnd();
    }
}


//========================================================================
// Window size callback function
//========================================================================

static void windowSizeFun(GLFWwindow window, int w, int h)
{
    width  = w;
    height = h > 0 ? h : 1;
    do_redraw = 1;
}


//========================================================================
// Window refresh callback function
//========================================================================

static void windowRefreshFun(GLFWwindow window)
{
    do_redraw = 1;
}


//========================================================================
// Mouse position callback function
//========================================================================

static void cursorPosFun(GLFWwindow window, int x, int y)
{
    // Depending on which view was selected, rotate around different axes
    switch (active_view)
    {
        case 1:
            rot_x += y - ypos;
            rot_z += x - xpos;
            do_redraw = 1;
            break;
        case 3:
            rot_x += y - ypos;
            rot_y += x - xpos;
            do_redraw = 1;
            break;
        case 4:
            rot_y += x - xpos;
            rot_z += y - ypos;
            do_redraw = 1;
            break;
        default:
            // Do nothing for perspective view, or if no view is selected
            break;
    }

    // Remember cursor position
    xpos = x;
    ypos = y;
}


//========================================================================
// Mouse button callback function
//========================================================================

static void mouseButtonFun(GLFWwindow window, int button, int action)
{
    if ((button == GLFW_MOUSE_BUTTON_LEFT) && action == GLFW_PRESS)
    {
        // Detect which of the four views was clicked
        active_view = 1;
        if (xpos >= width / 2)
            active_view += 1;
        if (ypos >= height / 2)
            active_view += 2;
    }
    else if (button == GLFW_MOUSE_BUTTON_LEFT)
    {
        // Deselect any previously selected view
        active_view = 0;
    }

    do_redraw = 1;
}


//========================================================================
// main
//========================================================================

int main(void)
{
    GLFWwindow window;
    int width, height;

    // Initialise GLFW
    if (!glfwInit())
    {
        fprintf(stderr, "Failed to initialize GLFW\n");
        exit(EXIT_FAILURE);
    }

    // Set callback functions
    glfwSetWindowSizeCallback(windowSizeFun);
    glfwSetWindowRefreshCallback(windowRefreshFun);
    glfwSetCursorPosCallback(cursorPosFun);
    glfwSetMouseButtonCallback(mouseButtonFun);

    glfwWindowHint(GLFW_DEPTH_BITS, 16);

    // Open OpenGL window
    window = glfwCreateWindow(500, 500, GLFW_WINDOWED, "Split view demo", NULL);
    if (!window)
    {
        fprintf(stderr, "Failed to open GLFW window\n");
        exit(EXIT_FAILURE);
    }

    glfwGetWindowSize(window, &width, &height);
    windowSizeFun(window, width, height);

    // Enable vsync
    glfwSwapInterval(1);

    // Enable sticky keys
    glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

    // Enable mouse cursor (only needed for fullscreen mode)
    glfwSetInputMode(window, GLFW_CURSOR_MODE, GLFW_CURSOR_NORMAL);

    // Main loop
    for (;;)
    {
        // Only redraw if we need to
        if (do_redraw)
        {
            // Draw all views
            drawAllViews();

            // Swap buffers
            glfwSwapBuffers(window);

            do_redraw = 0;
        }

        // Wait for new events
        glfwWaitEvents();

        // Check if the ESC key was pressed or the window should be closed
        if (glfwGetKey(window, GLFW_KEY_ESCAPE))
            break;
        if (glfwGetWindowParam(window, GLFW_CLOSE_REQUESTED))
            break;
    }

    // Close OpenGL window and terminate GLFW
    glfwTerminate();

    exit(EXIT_SUCCESS);
}