Dogcows Code - chaz/openbox/blob - render/imagecache.c

   1 /* -*- indent-tabs-mode: nil; tab-width: 4; c-basic-offset: 4; -*-
   2
   3    imagecache.c for the Openbox window manager
   4    Copyright (c) 2008        Dana Jansens
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    See the COPYING file for a copy of the GNU General Public License.
  17 */
  18
  19 #include "render.h"
  20 #include "imagecache.h"
  21 #include "image.h"
  22
  23 static gboolean RrImagePicEqual(const RrImagePic *p1,
  24                                 const RrImagePic *p2);
  25
  26 RrImageCache* RrImageCacheNew(gint max_resized_saved)
  27 {
  28     RrImageCache *self;
  29
  30     g_assert(max_resized_saved >= 0);
  31
  32     self = g_new(RrImageCache, 1);
  33     self->ref = 1;
  34     self->max_resized_saved = max_resized_saved;
  35     self->table = g_hash_table_new((GHashFunc)RrImagePicHash,
  36                                    (GEqualFunc)RrImagePicEqual);
  37     return self;
  38 }
  39
  40 void RrImageCacheRef(RrImageCache *self)
  41 {
  42     ++self->ref;
  43 }
  44
  45 void RrImageCacheUnref(RrImageCache *self)
  46 {
  47     if (self && --self->ref == 0) {
  48         g_assert(g_hash_table_size(self->table) == 0);
  49         g_hash_table_unref(self->table);
  50
  51         g_free(self);
  52     }
  53 }
  54
  55 /*! Finds an image in the cache, if it is already in there */
  56 RrImage* RrImageCacheFind(RrImageCache *self,
  57                           RrPixel32 *data, gint w, gint h)
  58 {
  59     RrImagePic pic;
  60
  61     RrImagePicInit(&pic, w, h, data);
  62     return g_hash_table_lookup(self->table, &pic);
  63 }
  64
  65 #define hashsize(n) ((RrPixel32)1<<(n))
  66 #define hashmask(n) (hashsize(n)-1)
  67 #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
  68 /* mix -- mix 3 32-bit values reversibly. */
  69 #define mix(a,b,c) \
  70 { \
  71   a -= c;  a ^= rot(c, 4);  c += b; \
  72   b -= a;  b ^= rot(a, 6);  a += c; \
  73   c -= b;  c ^= rot(b, 8);  b += a; \
  74   a -= c;  a ^= rot(c,16);  c += b; \
  75   b -= a;  b ^= rot(a,19);  a += c; \
  76   c -= b;  c ^= rot(b, 4);  b += a; \
  77 }
  78 /* final -- final mixing of 3 32-bit values (a,b,c) into c */
  79 #define final(a,b,c) \
  80 { \
  81   c ^= b; c -= rot(b,14); \
  82   a ^= c; a -= rot(c,11); \
  83   b ^= a; b -= rot(a,25); \
  84   c ^= b; c -= rot(b,16); \
  85   a ^= c; a -= rot(c,4);  \
  86   b ^= a; b -= rot(a,14); \
  87   c ^= b; c -= rot(b,24); \
  88 }
  89
  90 /* This is a fast, reversable hash function called "lookup3", found here:
  91    http://burtleburtle.net/bob/c/lookup3.c, by Bob Jenkins
  92
  93    This hashing algorithm is "reversible", that is, not cryptographically
  94    secure at all.  But we don't care about that, we just want something to
  95    tell when images are the same or different relatively quickly.
  96 */
  97 guint32 hashword(const guint32 *key, gint length, guint32 initval)
  98 {
  99     guint32 a,b,c;
 100
 101     /* Set up the internal state */
 102     a = b = c = 0xdeadbeef + (((guint32)length)<<2) + initval;
 103
 104     /* handle most of the key */
 105     while (length > 3)
 106     {
 107         a += key[0];
 108         b += key[1];
 109         c += key[2];
 110         mix(a,b,c);
 111         length -= 3;
 112         key += 3;
 113     }
 114
 115     /* handle the last 3 guint32's */
 116     switch(length)      /* all the case statements fall through */
 117     {
 118     case 3: c+=key[2];
 119     case 2: b+=key[1];
 120     case 1: a+=key[0];
 121         final(a,b,c);
 122     case 0:             /* case 0: nothing left to add */
 123         break;
 124     }
 125     /* report the result */
 126     return c;
 127 }
 128
 129 /*! This is some arbitrary initial value for the hashing function.  It's
 130   constant so that you get the same result from the same data each time.
 131 */
 132 #define HASH_INITVAL 0xf00d
 133
 134 guint RrImagePicHash(const RrImagePic *p)
 135 {
 136     return hashword(p->data, p->width * p->height, HASH_INITVAL);
 137 }
 138
 139 static gboolean RrImagePicEqual(const RrImagePic *p1,
 140                                 const RrImagePic *p2)
 141 {
 142     return p1->width == p2->width && p1->height == p2->height &&
 143         p1->sum == p2->sum;
 144 }