/*
  Copyright (C) 1997-2011 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely.
*/

/* Simple program:  Fill a colormap with gray and stripe it down the screen,
		    Then move an alpha valued sprite around the screen.
 */

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

#include "SDL.h"

#define FRAME_TICKS	(1000/30)       /* 30 frames/second */

/* Call this instead of exit(), so we can clean up SDL: atexit() is evil. */
static void
quit(int rc)
{
    SDL_Quit();
    exit(rc);
}

/* Fill the screen with a gradient */
static void
FillBackground(SDL_Surface * screen)
{
    Uint8 *buffer;
    Uint8 gradient;
    int i, k;

    /* Set the surface pixels and refresh! */
    if (SDL_LockSurface(screen) < 0) {
        fprintf(stderr, "Couldn't lock the display surface: %s\n",
                SDL_GetError());
        quit(2);
    }
    buffer = (Uint8 *) screen->pixels;
    switch (screen->format->BytesPerPixel) {
    case 1:
    case 3:
        for (i = 0; i < screen->h; ++i) {
            memset(buffer, (i * 255) / screen->h,
                   screen->w * screen->format->BytesPerPixel);
            buffer += screen->pitch;
        }
        break;
    case 2:
        for (i = 0; i < screen->h; ++i) {
            Uint16 *buffer16;
            Uint16 color;

            gradient = ((i * 255) / screen->h);
            color = (Uint16) SDL_MapRGB(screen->format,
                                        gradient, gradient, gradient);
            buffer16 = (Uint16 *) buffer;
            for (k = 0; k < screen->w; k++) {
                *buffer16++ = color;
            }
            buffer += screen->pitch;
        }
        break;
    case 4:
        for (i = 0; i < screen->h; ++i) {
            Uint32 *buffer32;
            Uint32 color;

            gradient = ((i * 255) / screen->h);
            color = SDL_MapRGB(screen->format, gradient, gradient, gradient);
            buffer32 = (Uint32 *) buffer;
            for (k = 0; k < screen->w; k++) {
                *buffer32++ = color;
            }
            buffer += screen->pitch;
        }
        break;
    }

    SDL_UnlockSurface(screen);
    SDL_UpdateRect(screen, 0, 0, 0, 0);
}

/* Create a "light" -- a yellowish surface with variable alpha */
SDL_Surface *
CreateLight(int radius)
{
    Uint8 trans, alphamask;
    int range, addition;
    int xdist, ydist;
    Uint16 x, y;
    Uint16 skip;
    Uint32 pixel;
    SDL_Surface *light;

#ifdef LIGHT_16BIT
    Uint16 *buf;

    /* Create a 16 (4/4/4/4) bpp square with a full 4-bit alpha channel */
    /* Note: this isn't any faster than a 32 bit alpha surface */
    alphamask = 0x0000000F;
    light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2 * radius, 2 * radius, 16,
                                 0x0000F000, 0x00000F00, 0x000000F0,
                                 alphamask);
#else
    Uint32 *buf;

    /* Create a 32 (8/8/8/8) bpp square with a full 8-bit alpha channel */
    alphamask = 0x000000FF;
    light = SDL_CreateRGBSurface(SDL_SWSURFACE, 2 * radius, 2 * radius, 32,
                                 0xFF000000, 0x00FF0000, 0x0000FF00,
                                 alphamask);
    if (light == NULL) {
        fprintf(stderr, "Couldn't create light: %s\n", SDL_GetError());
        return (NULL);
    }
#endif

    /* Fill with a light yellow-orange color */
    skip = light->pitch - (light->w * light->format->BytesPerPixel);
#ifdef LIGHT_16BIT
    buf = (Uint16 *) light->pixels;
#else
    buf = (Uint32 *) light->pixels;
#endif
    /* Get a tranparent pixel value - we'll add alpha later */
    pixel = SDL_MapRGBA(light->format, 0xFF, 0xDD, 0x88, 0);
    for (y = 0; y < light->h; ++y) {
        for (x = 0; x < light->w; ++x) {
            *buf++ = pixel;
        }
        buf += skip;            /* Almost always 0, but just in case... */
    }

    /* Calculate alpha values for the surface. */
#ifdef LIGHT_16BIT
    buf = (Uint16 *) light->pixels;
#else
    buf = (Uint32 *) light->pixels;
#endif
    for (y = 0; y < light->h; ++y) {
        for (x = 0; x < light->w; ++x) {
            /* Slow distance formula (from center of light) */
            xdist = x - (light->w / 2);
            ydist = y - (light->h / 2);
            range = (int) sqrt(xdist * xdist + ydist * ydist);

            /* Scale distance to range of transparency (0-255) */
            if (range > radius) {
                trans = alphamask;
            } else {
                /* Increasing transparency with distance */
                trans = (Uint8) ((range * alphamask) / radius);

                /* Lights are very transparent */
                addition = (alphamask + 1) / 8;
                if ((int) trans + addition > alphamask) {
                    trans = alphamask;
                } else {
                    trans += addition;
                }
            }
            /* We set the alpha component as the right N bits */
            *buf++ |= (255 - trans);
        }
        buf += skip;            /* Almost always 0, but just in case... */
    }
    /* Enable RLE acceleration of this alpha surface */
    SDL_SetAlpha(light, SDL_SRCALPHA | SDL_RLEACCEL, 0);

    /* We're done! */
    return (light);
}

static Uint32 flashes = 0;
static Uint32 flashtime = 0;

void
FlashLight(SDL_Surface * screen, SDL_Surface * light, int x, int y)
{
    SDL_Rect position;
    Uint32 ticks1;
    Uint32 ticks2;

    /* Easy, center light */
    position.x = x - (light->w / 2);
    position.y = y - (light->h / 2);
    position.w = light->w;
    position.h = light->h;
    ticks1 = SDL_GetTicks();
    SDL_BlitSurface(light, NULL, screen, &position);
    ticks2 = SDL_GetTicks();
    SDL_UpdateRects(screen, 1, &position);
    ++flashes;

    /* Update time spend doing alpha blitting */
    flashtime += (ticks2 - ticks1);
}

static int sprite_visible = 0;
static SDL_Surface *sprite;
static SDL_Surface *backing;
static SDL_Rect position;
static int x_vel, y_vel;
static int alpha_vel;

int
LoadSprite(SDL_Surface * screen, char *file)
{
    SDL_Surface *converted;

    /* Load the sprite image */
    sprite = SDL_LoadBMP(file);
    if (sprite == NULL) {
        fprintf(stderr, "Couldn't load %s: %s", file, SDL_GetError());
        return (-1);
    }

    /* Set transparent pixel as the pixel at (0,0) */
    if (sprite->format->palette) {
        SDL_SetColorKey(sprite, SDL_SRCCOLORKEY, *(Uint8 *) sprite->pixels);
    }

    /* Convert sprite to video format */
    converted = SDL_DisplayFormat(sprite);
    SDL_FreeSurface(sprite);
    if (converted == NULL) {
        fprintf(stderr, "Couldn't convert background: %s\n", SDL_GetError());
        return (-1);
    }
    sprite = converted;

    /* Create the background */
    backing = SDL_CreateRGBSurface(SDL_SWSURFACE, sprite->w, sprite->h, 8,
                                   0, 0, 0, 0);
    if (backing == NULL) {
        fprintf(stderr, "Couldn't create background: %s\n", SDL_GetError());
        SDL_FreeSurface(sprite);
        return (-1);
    }

    /* Convert background to video format */
    converted = SDL_DisplayFormat(backing);
    SDL_FreeSurface(backing);
    if (converted == NULL) {
        fprintf(stderr, "Couldn't convert background: %s\n", SDL_GetError());
        SDL_FreeSurface(sprite);
        return (-1);
    }
    backing = converted;

    /* Set the initial position of the sprite */
    position.x = (screen->w - sprite->w) / 2;
    position.y = (screen->h - sprite->h) / 2;
    position.w = sprite->w;
    position.h = sprite->h;
    x_vel = 0;
    y_vel = 0;
    alpha_vel = 1;

    /* We're ready to roll. :) */
    return (0);
}

void
AttractSprite(Uint16 x, Uint16 y)
{
    x_vel = ((int) x - position.x) / 10;
    y_vel = ((int) y - position.y) / 10;
}

void
MoveSprite(SDL_Surface * screen, SDL_Surface * light)
{
    SDL_Rect updates[2];
    Uint8 alpha;

    /* Erase the sprite if it was visible */
    if (sprite_visible) {
        updates[0] = position;
        SDL_BlitSurface(backing, NULL, screen, &updates[0]);
    } else {
        updates[0].x = 0;
        updates[0].y = 0;
        updates[0].w = 0;
        updates[0].h = 0;
        sprite_visible = 1;
    }

    /* Since the sprite is off the screen, we can do other drawing
       without being overwritten by the saved area behind the sprite.
     */
    if (light != NULL) {
        int x, y;

        SDL_GetMouseState(&x, &y);
        FlashLight(screen, light, x, y);
    }

    /* Move the sprite, bounce at the wall */
    position.x += x_vel;
    if ((position.x < 0) || (position.x >= screen->w)) {
        x_vel = -x_vel;
        position.x += x_vel;
    }
    position.y += y_vel;
    if ((position.y < 0) || (position.y >= screen->h)) {
        y_vel = -y_vel;
        position.y += y_vel;
    }

    /* Update transparency (fade in and out) */
    SDL_GetSurfaceAlphaMod(sprite, &alpha);
    if (((int) alpha + alpha_vel) < 0) {
        alpha_vel = -alpha_vel;
    } else if (((int) alpha + alpha_vel) > 255) {
        alpha_vel = -alpha_vel;
    }
    SDL_SetAlpha(sprite, SDL_SRCALPHA, (Uint8) (alpha + alpha_vel));

    /* Save the area behind the sprite */
    updates[1] = position;
    SDL_BlitSurface(screen, &updates[1], backing, NULL);

    /* Blit the sprite onto the screen */
    updates[1] = position;
    SDL_BlitSurface(sprite, NULL, screen, &updates[1]);

    /* Make it so! */
    SDL_UpdateRects(screen, 2, updates);
}

int
main(int argc, char *argv[])
{
    const SDL_VideoInfo *info;
    SDL_Surface *screen;
    int w, h;
    Uint8 video_bpp;
    Uint32 videoflags;
    int i, done;
    SDL_Event event;
    SDL_Surface *light;
    int mouse_pressed;
    Uint32 ticks, lastticks;


    /* Initialize SDL */
    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
        return (1);
    }

    /* Alpha blending doesn't work well at 8-bit color */
#ifdef _WIN32_WCE
    /* Pocket PC */
    w = 240;
    h = 320;
#else
    w = 640;
    h = 480;
#endif
    info = SDL_GetVideoInfo();
    if (info->vfmt->BitsPerPixel > 8) {
        video_bpp = info->vfmt->BitsPerPixel;
    } else {
        video_bpp = 16;
        fprintf(stderr, "forced 16 bpp mode\n");
    }
    videoflags = SDL_SWSURFACE;
    for (i = 1; argv[i]; ++i) {
        if (strcmp(argv[i], "-bpp") == 0) {
            video_bpp = atoi(argv[++i]);
            if (video_bpp <= 8) {
                video_bpp = 16;
                fprintf(stderr, "forced 16 bpp mode\n");
            }
        } else if (strcmp(argv[i], "-hw") == 0) {
            videoflags |= SDL_HWSURFACE;
        } else if (strcmp(argv[i], "-warp") == 0) {
            videoflags |= SDL_HWPALETTE;
        } else if (strcmp(argv[i], "-width") == 0 && argv[i + 1]) {
            w = atoi(argv[++i]);
        } else if (strcmp(argv[i], "-height") == 0 && argv[i + 1]) {
            h = atoi(argv[++i]);
        } else if (strcmp(argv[i], "-resize") == 0) {
            videoflags |= SDL_RESIZABLE;
        } else if (strcmp(argv[i], "-noframe") == 0) {
            videoflags |= SDL_NOFRAME;
        } else if (strcmp(argv[i], "-fullscreen") == 0) {
            videoflags |= SDL_FULLSCREEN;
        } else {
            fprintf(stderr,
                    "Usage: %s [-width N] [-height N] [-bpp N] [-warp] [-hw] [-fullscreen]\n",
                    argv[0]);
            quit(1);
        }
    }

    /* Set video mode */
    if ((screen = SDL_SetVideoMode(w, h, video_bpp, videoflags)) == NULL) {
        fprintf(stderr, "Couldn't set %dx%dx%d video mode: %s\n",
                w, h, video_bpp, SDL_GetError());
        quit(2);
    }
    FillBackground(screen);

    /* Create the light */
    light = CreateLight(82);
    if (light == NULL) {
        quit(1);
    }

    /* Load the sprite */
    if (LoadSprite(screen, "icon.bmp") < 0) {
        SDL_FreeSurface(light);
        quit(1);
    }

    /* Print out information about our surfaces */
    printf("Screen is at %d bits per pixel\n", screen->format->BitsPerPixel);
    if ((screen->flags & SDL_HWSURFACE) == SDL_HWSURFACE) {
        printf("Screen is in video memory\n");
    } else {
        printf("Screen is in system memory\n");
    }
    if ((screen->flags & SDL_DOUBLEBUF) == SDL_DOUBLEBUF) {
        printf("Screen has double-buffering enabled\n");
    }
    if ((sprite->flags & SDL_HWSURFACE) == SDL_HWSURFACE) {
        printf("Sprite is in video memory\n");
    } else {
        printf("Sprite is in system memory\n");
    }

    /* Run a sample blit to trigger blit acceleration */
    MoveSprite(screen, NULL);
    if ((sprite->flags & SDL_HWACCEL) == SDL_HWACCEL) {
        printf("Sprite blit uses hardware alpha acceleration\n");
    } else {
        printf("Sprite blit dosn't uses hardware alpha acceleration\n");
    }

    /* Set a clipping rectangle to clip the outside edge of the screen */
    {
        SDL_Rect clip;
        clip.x = 32;
        clip.y = 32;
        clip.w = screen->w - (2 * 32);
        clip.h = screen->h - (2 * 32);
        SDL_SetClipRect(screen, &clip);
    }

    /* Wait for a keystroke */
    lastticks = SDL_GetTicks();
    done = 0;
    mouse_pressed = 0;
    while (!done) {
        /* Update the frame -- move the sprite */
        if (mouse_pressed) {
            MoveSprite(screen, light);
            mouse_pressed = 0;
        } else {
            MoveSprite(screen, NULL);
        }

        /* Slow down the loop to 30 frames/second */
        ticks = SDL_GetTicks();
        if ((ticks - lastticks) < FRAME_TICKS) {
#ifdef CHECK_SLEEP_GRANULARITY
            fprintf(stderr, "Sleeping %d ticks\n",
                    FRAME_TICKS - (ticks - lastticks));
#endif
            SDL_Delay(FRAME_TICKS - (ticks - lastticks));
#ifdef CHECK_SLEEP_GRANULARITY
            fprintf(stderr, "Slept %d ticks\n", (SDL_GetTicks() - ticks));
#endif
        }
        lastticks = ticks;

        /* Check for events */
        while (SDL_PollEvent(&event)) {
            switch (event.type) {
            case SDL_VIDEORESIZE:
                screen =
                    SDL_SetVideoMode(event.resize.w, event.resize.h,
                                     video_bpp, videoflags);
                if (screen) {
                    FillBackground(screen);
                }
                break;
                /* Attract sprite while mouse is held down */
            case SDL_MOUSEMOTION:
                if (event.motion.state != 0) {
                    AttractSprite(event.motion.x, event.motion.y);
                    mouse_pressed = 1;
                }
                break;
            case SDL_MOUSEBUTTONDOWN:
                if (event.button.button == 1) {
                    AttractSprite(event.button.x, event.button.y);
                    mouse_pressed = 1;
                } else {
                    SDL_Rect area;

                    area.x = event.button.x - 16;
                    area.y = event.button.y - 16;
                    area.w = 32;
                    area.h = 32;
                    SDL_FillRect(screen, &area,
                                 SDL_MapRGB(screen->format, 0, 0, 0));
                    SDL_UpdateRects(screen, 1, &area);
                }
                break;
            case SDL_KEYDOWN:
                if (event.key.keysym.sym == SDLK_ESCAPE) {
                    done = 1;
                }
                if (event.key.keysym.sym == SDLK_RETURN) {
                    SDL_WM_ToggleFullScreen(screen);
                }
                break;
            case SDL_QUIT:
                done = 1;
                break;
            default:
                break;
            }
        }
    }
    SDL_FreeSurface(light);
    SDL_FreeSurface(sprite);
    SDL_FreeSurface(backing);

    /* Print out some timing information */
    if (flashes > 0) {
        printf("%d alpha blits, ~%4.4f ms per blit\n",
               flashes, (float) flashtime / flashes);
    }

    SDL_Quit();
    return (0);
}