ex1.c

/*=========================================================================

GFX EXAMPLE CODE - #1
        "pixel stars"

Copyright (C) 2004  Rafael de Oliveira Jannone

This example's source code is Public Domain.

WARNING: The author makes no guarantees and holds no responsibility for 
any damage, injury or loss that may result from the use of this source 
code. USE IT AT YOUR OWN RISK.

Contact the author:
        by e-mail : rafael AT jannone DOT org
        homepage  : http://jannone.org/gfxlib
        ICQ UIN   : 10115284

=========================================================================*/

#include <stdlib.h>
#include "gfx.h"

typedef struct {
        int x;
        int y;
        int z;
        u_int addr, last;
        u_char sub;
} star_t;

void star_randomize(star_t* st) {
        st->x = i2f((rand() & 63) - 32);
        st->y = i2f((rand() & 63) - 32);
        st->z = 64;
}

void star_move(star_t* st) {
        int x, y, z;
        z = (st->z -= 2);
        x = f2i(divfx(st->x, z)) + 128;
        y = f2i(divfx(st->y, z)) + 96;
        if (z < 1 || x < 0 || x >= MODE2_WIDTH || y < 0 || y >= MODE2_HEIGHT) {
                star_randomize(st);
                z = st->z;
                x = f2i(divfx(st->x, z)) + 128;
                y = f2i(divfx(st->y, z)) + 96;
        }
        st->last = st->addr;
        st->addr = map_pixel(x, y);
        st->sub  = map_subpixel(x);
}

#define MAX_STARS 16

main() {
        u_char c;
        star_t *st, stars[MAX_STARS];

        set_color(15, 1, 1);

        // set video mode to screen 2
        set_mode(mode_2);

        // set whole screen to color white/black
        fill(MODE2_ATTR, 0xf1, MODE2_MAX);

        // initialize stars
        for (c=0; c < MAX_STARS; c++) {
                st = stars + c;
                star_randomize(st);
                st->z = (rand() & 63) << 2;
                st->addr = 0;
        }

        // animation loop
        while (!get_trigger(0)) {
                // calculate star movement
                for (st=stars, c=0; c < MAX_STARS; c++, st++)
                        star_move(st);

                // erase previous stars
                for (st=stars, c=0; c < MAX_STARS; c++, st++)
                        vpoke(st->last, 0);

                // show new stars
                for (st=stars, c=0; c < MAX_STARS; c++, st++)
                        vmerge(st->addr, st->sub);
        }

        set_mode(mode_0);
}

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