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better hash for worley

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This commit is contained in:
John Cupitt 2016-07-19 12:29:36 +01:00
parent e14c97359a
commit 99766dbd83
1 changed files with 23 additions and 13 deletions
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36
libvips/create/worley.c
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@ -60,7 +60,7 @@ typedef struct _VipsWorley {
/* Use this to seed this call of our rng.
*/
int seed;
guint32 seed;
} VipsWorley;
typedef struct _VipsWorleyClass {
@ -112,12 +112,19 @@ typedef struct _Sequence {
} Sequence;
/* A very simple random number generator.
/* A very simple random number generator. See:
* http://isthe.com/chongo/tech/comp/fnv/#FNV-source
*/
static int
vips_worley_random( int previous )
static guint32
vips_worley_random( guint32 seed )
{
return( ((guint64) 1103515245 * previous + 12345) & 0xffffff );
return( 1103515245u * seed + 12345 );
}
static guint32
vips_worley_seed_add( guint32 seed, int value )
{
return( ((2166136261u ^ seed) * 16777619u) ^ value );
}
/* Generate a 3 x 3 grid of cells around a point.
@ -132,7 +139,8 @@ vips_worley_create_cells( VipsWorley *worley,
for( x = 0; x < 3; x++ ) {
Cell *cell = &cells[x + y * 3];
int seed;
guint32 seed;
int value;
int j;
/* Can go <0 and >width for edges.
@ -146,18 +154,20 @@ vips_worley_create_cells( VipsWorley *worley,
* around so that our output will tesselate.
*/
if( cell->cell_x >= worley->cells_across )
seed ^= 0;
value = 0;
else if( cell->cell_x < 0 )
seed ^= worley->cells_across - 1;
value = worley->cells_across - 1;
else
seed ^= cell->cell_x;
value = cell->cell_x;
seed = vips_worley_seed_add( seed, value );
if( cell->cell_y >= worley->cells_down )
seed ^= 0;
value = 0;
else if( cell->cell_y < 0 )
seed ^= worley->cells_down - 1;
value = worley->cells_down - 1;
else
seed ^= cell->cell_y;
value = cell->cell_y;
seed = vips_worley_seed_add( seed, value );
/* [1, MAX_FEATURES)
*/
@ -286,7 +296,7 @@ vips_worley_build( VipsObject *object )
worley->cells_down = ROUND_UP( worley->height, worley->cell_size ) /
worley->cell_size;
worley->seed = g_random_double() * 0xffffff;
worley->seed = g_random_double() * 0xffffffffu;
vips_image_init_fields( create->out,
worley->width, worley->height, 1,