src/add-ons/screen_savers/nebula/Draw.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 "Draw.h"
  12
  13
  14 // Hand-translated from x86 assembly.
  15 /* memshset (char *dst, int center_shade,int fixed_shade, int length_2) */
  16 /* dst is the *center* of the dst segment */
  17 /* center shade is the initial color (at center) (!! 8:8 also) */
  18 /* fixed_shade is the fixed point increment (8:8) */
  19 /* length_2 is the 1/2 length to set (to the left, and to the right) */
  20
  21 /* a memaddshadedset function (or something like that ) */
  22 void memshset(char* dstParam, int center_shade, int fixed_shade, int half_length)
  23 {
  24         unsigned char* dst;
  25         unsigned char* source;
  26         int offset;
  27
  28         if (half_length == 0)
  29                 return;
  30
  31         dst = (unsigned char*)dstParam;
  32         source = dst;
  33         dst -= half_length; // Left segment
  34         source += half_length; // Right segment
  35         source++; // Don't overlap at middle
  36
  37         offset = half_length;
  38         offset = -offset;
  39         offset--; // For in-advance incl in loop
  40
  41         do {
  42                 int tmp;
  43                 center_shade += fixed_shade; // Increment color.
  44                 center_shade &= 0xFFFF; // Mask so we can do overflow tests.
  45                 offset++;
  46
  47                 tmp = dst[half_length] + (center_shade >> 8); // Increment left pixel.
  48                 // Did it overflow?
  49                 if (tmp & 0xFF00)
  50                         dst[half_length] = 255;
  51                 else
  52                         dst[half_length] = tmp;
  53
  54                 tmp = source[offset] + (center_shade >> 8); // Increment right pixel.
  55                 if (tmp & 0xFF00)
  56                         source[offset] = 255;
  57                 else
  58                         source[offset] = tmp;
  59         } while (--half_length != 0);
  60 }
  61
  62
  63 /* do the "motion blur" (actually the pixel fading) */
  64 void mblur(char* srcParam, int nbpixels)
  65 {
  66         unsigned int clear1UpperBit = 0x7f7f7f7f;
  67         unsigned int clear3UpperBits = 0x1f1f1f1f;
  68         unsigned int* src = (unsigned int*)srcParam;
  69
  70         if ((nbpixels >>= 2) == 0)
  71                 return;
  72
  73         do {
  74                 unsigned int eax, ebx;
  75                 eax = *src;
  76
  77                 ebx = eax;
  78                 eax >>= 1;
  79
  80                 ebx >>= 3;
  81                 eax &= clear1UpperBit;
  82
  83                 ebx &= clear3UpperBits;
  84
  85                 eax += ebx;
  86                 *src = eax;
  87                 src++;
  88         } while (--nbpixels != 0);
  89 }