SDL2/test/testalpha.c

/* 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(0, &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;
                }
                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);
}