/* sdl.c
 *
 * Kamil Kaminski
 * kkaminsk.com
 *
 * Skeleton for SDL
 *
 *
 */
 
#include <SDL/SDL.h>
#include <SDL/SDL_image.h>
#include <GL/glew.h>
#include <GL/freeglut.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

/* function prototypes */
static void gltErrorCheck(void);
static void resize(int, int);
static void setup_opengl(void);
static void keys(SDL_keysym *, unsigned int *);
static void process_events(void);
static void render(void);

/* global */
int program_running = 1;

/* few light arrays */
const GLfloat fNoLight[]     = { 0.0f, 0.0f, 0.0f, 1.0f    };
const GLfloat fLowLight[]    = { 0.25f, 0.25f, 0.25f, 1.0f };
const GLfloat fMedLight[]    = { 0.50f, 0.50f, 0.50f, 1.0f };
const GLfloat fShinyLight[]  = { 0.70f, 0.70f, 0.70f, 1.0f };
const GLfloat fBrightLight[] = { 1.0f, 1.0f, 1.0f, 1.0f    };

/* light values and coordinates */
const GLfloat lightPos[]     = { -10.f, 5.0f, 5.0f, 1.0f   };

static void gltErrorCheck(void)
{
    GLenum err_code;
    const GLubyte *err_str;

    while ((err_code = glGetError()) != GL_NO_ERROR)
    {
        err_str = gluErrorString(err_code);
        fprintf(stderr, "OpenGL error: %s\n", err_str);
    }
}

static void resize(int w, int h)
{
    printf("window: resizing to %dx%d\n", w, h);
    GLfloat fAspect = (GLfloat) w / (GLfloat) h;
    if (h == 0)
        h = 1;
    glViewport(0, 0, w, h);

    /* reset coordinate system */
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    /* produce the perspective projection */
    /* void gluPerspective(GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar) */
    gluPerspective(40.0f, fAspect, 1.0, 40.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    
    /* this needs to be ran again, glut does it for you I suppose */
    SDL_SetVideoMode(w, h, 32, SDL_OPENGL | SDL_RESIZABLE);
}

static void setup_opengl(void)
{
    /* setup fog */
    glEnable(GL_FOG);
    glFogfv(GL_FOG_COLOR, fLowLight); /* set fog color to match background */
    glFogf(GL_FOG_START, 4.0f);
    glFogf(GL_FOG_END, 20.0f);
    glFogi(GL_FOG_MODE, GL_LINEAR);   /* fog equation */

    glEnable(GL_DEPTH_TEST); /* hidden surface removal, aka Z-buffer */
    glFrontFace(GL_CCW);     /* counter clock-wise polygons face out */
    glEnable(GL_CULL_FACE);  /* do not calculate inside of a pyramid */

    /* enable lighting, primitives now need to define color properties */
    glEnable(GL_LIGHTING);

    /* global illumination, ambient RGBA intensity of the entire scene */
    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, fLowLight);

    /* setup and enable light 0 */
    glLightfv(GL_LIGHT0, GL_AMBIENT,  fMedLight);
    glLightfv(GL_LIGHT0, GL_DIFFUSE,  fShinyLight);
    glLightfv(GL_LIGHT0, GL_SPECULAR, fBrightLight);
    glLightfv(GL_LIGHT0, GL_POSITION, lightPos);
    glEnable(GL_LIGHT0);

    /* set material properties to follow all glColor values */
    /* all primitives specified after the glMaterial call are affected by the
     * last values set, until another call to glMaterial is made */
    glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE);

    /* enable color tracking, should be called after glColorMaterial */
    glEnable(GL_COLOR_MATERIAL);

    /* set globally, sets specular reflection to a white color,
     * this call follows all subsequent primitives */
    glMaterialfv(GL_FRONT, GL_SPECULAR, fBrightLight);

    /* default (0), by increasing this value you reduce the size and increase
     * the focus of the specular highlight, causing a shiny spot to appear */
    glMateriali(GL_FRONT, GL_SHININESS, 64);

    /* multisampling for polygons, conflicts with *polygon* anti-aliasing */
    /* enabled by default, that's what man page says, hmmm! */
    glEnable(GL_MULTISAMPLE);

    /* AA is disabled, but we will keep the blending function and hints though */
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glHint(GL_POINT_SMOOTH_HINT, GL_NICEST);
    glHint(GL_LINE_SMOOTH_HINT, GL_NICEST);

    /* anisotropic filtering */
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 8);

    /* how OpenGL combines the colors from texels with the color of the underlying
     * geometry is controlled by the texture environment mode */
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

    /* once texture is loaded and enabled, it will applied to every primitive
     * that specifies coordinates, ORLY? */
    glEnable(GL_TEXTURE_2D);

    /* specular highlights for textured items */
    glLightModeli(GL_LIGHT_MODEL_COLOR_CONTROL, GL_SEPARATE_SPECULAR_COLOR);

    /* gray background */
    glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
}

static void keys(SDL_keysym *keysym, unsigned int *keys_held)
{
    switch (keysym->sym)
    {
    case SDLK_ESCAPE:
        program_running = 0;
        break;
    default:
        break;
    }
}

/* process SDL events */
static void process_events(void)
{
    SDL_Event event;
    unsigned static int keys_held[323];
    SDLKey sym;
    
    while (SDL_PollEvent(&event))
    {
        sym = event.key.keysym.sym;
    
        switch (event.type)
        {
            case SDL_KEYUP:
            {
                /* reset the key to 0 */
                keys_held[sym] = 0;
                break;
            }
            case SDL_KEYDOWN:
            {
                keys_held[sym] = 1;
                keys(&event.key.keysym, keys_held);
                break;
            }
            case SDL_VIDEORESIZE:
            {
                resize(event.resize.w, event.resize.h);
                break;
            }
            case SDL_QUIT:
            {
                program_running = 0;
                break;
            }
            default:
                break;
        }
    }
}

static void render(void)
{                              
    /* clear the window with current clearing color */
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    /* save the matrix state and do the rotations */
    glPushMatrix();

    glDisable(GL_MULTISAMPLE);
    glEnable(GL_BLEND);
    glEnable(GL_LINE_SMOOTH);

    GLfloat fExtent = 20.0f;
    GLfloat fStep = 0.5f;
    GLfloat y = -0.4f;
    GLfloat iLine;

    glLineWidth(1.0f);
    glBegin(GL_LINES);
    for (iLine = -fExtent; iLine <= fExtent; iLine += fStep)
    {
        glVertex3f(iLine, y, fExtent);
        glVertex3f(iLine, y, -fExtent);
        glVertex3f(fExtent, y, iLine);
        glVertex3f(-fExtent, y, iLine);
    }
    glEnd();

    glDisable(GL_LINE_SMOOTH);
    glDisable(GL_BLEND);
    glEnable(GL_MULTISAMPLE);

    /* restore the matrix state */
    glPopMatrix();

    /* buffer swap */
    SDL_GL_SwapBuffers();
}

int main(int argc, char **argv)
{
    SDL_Surface *screen;

    if (SDL_Init(SDL_INIT_VIDEO) < 0 )
    {
        fprintf(stderr, "SDL: unable to init, %s\n", SDL_GetError());
        exit(-1);
    }
    atexit(SDL_Quit);
    SDL_WM_SetCaption("SDL", NULL);

    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);

    if ((screen = SDL_SetVideoMode(640, 480, 32, SDL_OPENGL | SDL_RESIZABLE)) == NULL)
    {
        fprintf(stderr, "SDL: unable to set video mode: %s\n", SDL_GetError());
        exit(-1);
    }
    
    SDL_EnableUNICODE(1);
    /* SDL doesn't trigger off a ResizeEvent at startup, but as we need this 
     * for OpenGL, we do this ourselves */
    SDL_Event resizeEvent;
    resizeEvent.type = SDL_VIDEORESIZE;
    resizeEvent.resize.w = 640;
    resizeEvent.resize.h = 480;
    SDL_PushEvent(&resizeEvent);
    
    /* initalize glew */
    GLenum glewerr = glewInit();
    if (GLEW_OK != glewerr)
    {
        fprintf(stderr, "GLEW error: %s\n", glewGetErrorString(glewerr));
        exit(-1);
    }
    else
        fprintf(stdout, "GLEW: using version %s\n", glewGetString(GLEW_VERSION));

    /* display OpenGL version */
    GLint major;
    GLint minor;
    glGetIntegerv(GL_MAJOR_VERSION, &major);
    glGetIntegerv(GL_MINOR_VERSION, &minor);
    fprintf(stdout, "GLEW: initialized OpenGL %d.%d\n", major, minor);

    setup_opengl();
    gltErrorCheck();

    while (program_running)
    {
        process_events();
        render();
    }

    gltErrorCheck();
    SDL_FreeSurface(screen);
    puts("bye!");
    
    return 0;
}