src/add-ons/screen_savers/nebula/DrawStars.c

   1 /*
   2  * Copyright 2004, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
   3  * Copyright 2015, Augustin Cavalier <waddlesplash>. All rights reserved.
   4  * Distributed under the terms of the MIT License.
   5  *
   6  * Effect from corTeX / Optimum.
   7  */
   8
   9 #include <SupportDefs.h>
  10
  11 #include "DrawStars.h"
  12
  13
  14 // Hand-translated from x86 assembly.
  15 /* draw a star (5 pixels) */
  16 void draw_stars(int star_width, char* dstParam, char incParam)
  17 {
  18         unsigned char* dst;
  19         unsigned char inc, al, cl;
  20         dst = (unsigned char*)dstParam;
  21         inc = (unsigned char)incParam;
  22
  23         dst[star_width] += inc;
  24         if (dst[star_width] < inc) {
  25                 // Overflowed.
  26                 dst[star_width] = 255;
  27         }
  28
  29         inc >>= 1;
  30         cl = dst[star_width - 1];
  31         cl += inc;
  32         if (cl < inc) {
  33                 *dst = 255;
  34                 dst[star_width - 1] = 255;
  35         } else {
  36                 al = *dst;
  37                 al += inc;
  38                 if (al >= inc)
  39                         *dst = al;
  40                 else
  41                         *dst = 255;
  42                 dst[star_width - 1] = cl;
  43         }
  44
  45         al = dst[star_width * 2];
  46         cl = dst[star_width + 1];
  47         al += inc;
  48         cl += inc;
  49         if (al < inc) {
  50                 if (cl >= inc) {
  51                         dst[star_width * 2] = 255;
  52                         dst[star_width + 1] = cl;
  53                         return;
  54                 }
  55         } else {
  56                 if (cl >= inc) {
  57                         dst[star_width * 2] = al;
  58                         dst[star_width + 1] = cl;
  59                         return;
  60                 }
  61         }
  62
  63         dst[star_width * 2] = 255;
  64         dst[star_width + 1] = 255;
  65 }