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slacy/twilight.c

Created February 10, 2015 21:49
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  1. slacy created this gist Feb 10, 2015.
    221 changes: 221 additions & 0 deletions twilight.c
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    /*
    *
    * cc twilight.c -lgl_s -lm -o twilight
    *
    * Copyright (c) 1991, 1992 Silicon Graphics, Inc.
    *
    * Permission to use, copy, modify, distribute, and sell this software and
    * its documentation for any purpose is hereby granted without fee, provided
    * that the name of Silicon Graphics may not be used in any advertising or
    * publicity relating to the software without the specific, prior written
    * permission of Silicon Graphics.
    *
    * THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND,
    * EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY
    * WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
    *
    * IN NO EVENT SHALL SILICON GRAPHICS BE LIABLE FOR ANY SPECIAL, INCIDENTAL,
    * INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND, OR ANY DAMAGES WHATSOEVER
    * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER OR NOT ADVISED OF THE
    * POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF LIABILITY, ARISING OUT OF OR IN
    * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
    */

    /*
    * A background/root window that looks like the twilight sky.
    * Howard Look
    */

    #include <gl/gl.h>
    #include <gl/device.h>
    #include <math.h>

    /* prototypes */
    void draw_background(float x, float y, Boolean rgb_mode);
    long star_color(float y, float max_y);

    /* point in y where color transition occurs */
    #define TRANSITION 0.2
    #define NUM_SMALL_STARS 2500
    #define NUM_BIG_STARS 200

    /* colors */
    static long orange[] = {255,72,0};
    static long blueish[] = {0,110,189};
    static long black[] = {0,0,0};

    static unsigned short half[16] = {
    0x5555, 0xAAAA, 0x5555, 0xAAAA,
    0x5555, 0xAAAA, 0x5555, 0xAAAA,
    0x5555, 0xAAAA, 0x5555, 0xAAAA,
    0x5555, 0xAAAA, 0x5555, 0xAAAA};

    main()
    {
    long gid, sizex, sizey;
    Boolean redraw_needed = FALSE;
    Boolean rgb_mode;
    short val;
    long dev;

    rgb_mode =
    getgdesc(GD_BITS_NORM_SNG_RED) &&
    getgdesc(GD_BITS_NORM_SNG_GREEN) &&
    getgdesc(GD_BITS_NORM_SNG_BLUE);

    imakebackground();
    gid = winopen("");
    if (rgb_mode)
    RGBmode();
    gconfig();

    if (!rgb_mode)
    defpattern(1,16,half);

    qenter(REDRAW,gid);

    while (1)
    {
    if (redraw_needed)
    {
    getsize(&sizex, &sizey);
    ortho2(-.5, (float)sizex-.5, -.5, (float)sizey-.5);
    viewport(0, sizex-1, 0, sizey-1);
    draw_background((float)sizex, (float)sizey, rgb_mode);
    redraw_needed = FALSE;
    }

    while (qtest() || (! redraw_needed))
    {
    dev = qread(&val);
    if (dev == REDRAW)
    redraw_needed = TRUE;
    }
    }
    }


    void draw_background(float x, float y, Boolean rgb_mode)
    {
    int i,j;
    float v1[2],v2[2],v3[2],v4[2];

    v1[0] = v4[0] = 0.0;
    v2[0] = v3[0] = x;

    v1[1] = v2[1] = 0.0;
    v3[1] = v4[1] = y*TRANSITION;

    if (rgb_mode)
    {
    bgnpolygon();
    c3i(orange);
    v2f(v1);
    v2f(v2);
    c3i(blueish);
    v2f(v3);
    v2f(v4);
    endpolygon();

    v1[1] = v2[1] = y;
    bgnpolygon();
    c3i(blueish);
    v2f(v4);
    v2f(v3);
    c3i(black);
    v2f(v2);
    v2f(v1);
    endpolygon();
    }
    else
    {
    color(BLACK);
    clear();
    color(BLUE);
    setpattern(1);
    clear();
    setpattern(0);
    }

    srand48(0); /* seed so stars are always the same */

    bgnpoint();
    for (i = 0; i < NUM_SMALL_STARS; i++)
    {
    float v[2];

    v[0] = x*drand48();
    v[1] = y*drand48();

    if (rgb_mode)
    cpack(star_color(v[1], y));
    else
    color(WHITE);

    v2f(v);
    }
    endpoint();

    for (i = 0; i < NUM_BIG_STARS; i++)
    {
    float v[2], size;

    v[0] = x*drand48();
    v[1] = y*drand48();
    size = drand48();

    pushmatrix();
    translate(v[0],v[1],0.0);
    scale(size,size,size);

    if (rgb_mode)
    cpack(star_color(v[1], y));
    else
    color(WHITE);

    sboxf(0.0,1.0,3.0,2.0);
    sboxf(1.0,0.0,2.0,3.0);
    popmatrix();
    }

    swapbuffers();
    }


    long
    star_color(float y, float max_y)
    {
    int r,g,b;
    float a;
    float ratio;

    if (y > max_y/2)
    return(0xFFFFFF);

    if (y < TRANSITION*max_y)
    {
    ratio = y / (max_y * TRANSITION);

    r = orange[0]*(1.0 - ratio) + blueish[0]*ratio;
    g = orange[1]*(1.0 - ratio) + blueish[1]*ratio;
    b = orange[2]*(1.0 - ratio) + blueish[2]*ratio;
    }
    else
    {
    ratio = (y - max_y*TRANSITION)/(max_y - max_y*TRANSITION);

    r = blueish[0]*(1.0 - ratio) + black[0]*ratio;
    g = blueish[1]*(1.0 - ratio) + black[1]*ratio;
    b = blueish[2]*(1.0 - ratio) + black[2]*ratio;
    }

    /* r,g and b are now the sky color at y, now blend with white */

    a = (y/(max_y/2.0));

    r = r*(1.0-a) + 255*a;
    g = g*(1.0-a) + 255*a;
    b = b*(1.0-a) + 255*a;

    return (r&0xff) + ((g&0xff)<<8) + ((b&0xff)<<16);
    }