make vips_gaussnoise() pixels reproducible

previously, pixel values were regenerated on every calculation, so they
changed on recomputation

pixel values are now generated from the pixel (x, y) coordinate plus a per-call
seed

thanks MvGulik, see

https://github.com/jcupitt/nip2/issues/60

https://github.com/jcupitt/libvips/issues/583

ChangeLog

@@ -28,6 +28,7 @@
 - kick load operations from cache on read error, thanks gaillard 
 - fix return from C++ assignment operator overloads (+=, -= etc) 
 - add @max_slope to vips_local_hist() to implement CLAHE, thanks hunter-87
+- vips_gaussnoise() pixels are reproducible on recalc, thanks MvGulik
 
 8/12/16 started 8.4.5
 - allow libgsf-1.14.26 to help centos, thanks tdiprima

libvips/create/gaussnoise.c

@@ -22,6 +22,10 @@
  * 	- redo as a class
  * 8/11/14
  * 	- use g_random_double()
+ * 24/1/17
+ * 	- use g_random_double() once per image, use vips__random() for pixel
+ * 	  values from (x, y) position ... makes pixels reproducible on
+ * 	  recalculation
  */
 
 /*
@@ -71,6 +75,9 @@ typedef struct _VipsGaussnoise {
 	double mean;
 	double sigma;
 
+	/* Per-image seed. 
+	 */
+	guint32 seed;
 } VipsGaussnoise;
 
 typedef VipsCreateClass VipsGaussnoiseClass;
@@ -93,12 +100,19 @@ vips_gaussnoise_gen( VipsRegion *or, void *seq, void *a, void *b,
 		int x;
 
 		for( x = 0; x < sz; x++ ) {
+			guint32 seed;
 			double sum;
 			int i;
 
+			seed = gaussnoise->seed;
+			seed = vips__random_add( seed, or->valid.left + x );
+			seed = vips__random_add( seed, or->valid.top + y );
+
 			sum = 0.0;
-			for( i = 0; i < 12; i++ ) 
+			for( i = 0; i < 12; i++ ) {
-				sum += g_random_double(); 
+				seed = vips__random( seed ); 
+				sum += (double) seed / UINT_MAX;
+			}
 
 			q[x] = (sum - 6.0) * gaussnoise->sigma + 
 				gaussnoise->mean;
@@ -124,6 +138,11 @@ vips_gaussnoise_build( VipsObject *object )
 	vips_image_pipelinev( create->out, 
 		VIPS_DEMAND_STYLE_ANY, NULL );
 
+	/* The seed for this image. Each pixel is seeded by this plus the (x,
+	 * y) coordinate.
+	 */
+	gaussnoise->seed = UINT_MAX * g_random_double(); 
+
 	if( vips_image_generate( create->out, 
 		NULL, vips_gaussnoise_gen, NULL, gaussnoise, NULL ) )
 		return( -1 );

libvips/create/perlin.c

@@ -92,21 +92,6 @@ typedef struct _Sequence {
 
 } Sequence;
 
-/* A very simple random number generator. See:
- * http://isthe.com/chongo/tech/comp/fnv/#FNV-source
- */
-static guint32
-vips_perlin_random( guint32 seed )
-{
-	return( 1103515245u * seed + 12345 );
-}
-
-static guint32 
-vips_perlin_seed_add( guint32 seed, int value )
-{
-	return( ((2166136261u ^ seed) * 16777619u) ^ value );
-}
-
 /* Generate a 3 x 3 grid of cells around a point. 
  */
 static void
@@ -135,13 +120,12 @@ vips_perlin_create_cells( VipsPerlin *perlin,
 
 			if( cy >= perlin->cells_down )
 				cy = 0;
-			seed = vips_perlin_seed_add( seed, cy );
+			seed = vips__random_add( seed, cy );
 
 			if( cx >= perlin->cells_across )
 				cx = 0;
-			seed = vips_perlin_seed_add( seed, cx );
+			seed = vips__random_add( seed, cx );
 
-			seed = vips_perlin_random( seed ); 
 			angle = (seed ^ (seed >> 8) ^ (seed >> 16)) & 0xff;
 
 			gx[ci] = vips_perlin_cos[angle];

libvips/create/worley.c

@@ -107,21 +107,6 @@ typedef struct _Sequence {
 
 } Sequence;
 
-/* A very simple random number generator. See:
- * http://isthe.com/chongo/tech/comp/fnv/#FNV-source
- */
-static guint32
-vips_worley_random( guint32 seed )
-{
-	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. 
  */
 static void
@@ -154,7 +139,7 @@ vips_worley_create_cells( VipsWorley *worley,
 				value = worley->cells_across - 1;
 			else 
 				value = cell->cell_x;
-			seed = vips_worley_seed_add( seed, value );
+			seed = vips__random_add( seed, value );
 
 			if( cell->cell_y >= worley->cells_down )
 				value = 0;
@@ -162,20 +147,19 @@ vips_worley_create_cells( VipsWorley *worley,
 				value = worley->cells_down - 1;
 			else 
 				value = cell->cell_y;
-			seed = vips_worley_seed_add( seed, value );
+			seed = vips__random_add( seed, value );
 
 			/* [1, MAX_FEATURES)
 			 */
-			seed = vips_worley_random( seed ); 
 			cell->n_features = (seed % (MAX_FEATURES - 1)) + 1;
 
 			for( j = 0; j < cell->n_features; j++ ) {
-				seed = vips_worley_random( seed ); 
+				seed = vips__random( seed ); 
 				cell->feature_x[j] = 
 					cell->cell_x * worley->cell_size + 
 					seed % worley->cell_size;
 
-				seed = vips_worley_random( seed ); 
+				seed = vips__random( seed ); 
 				cell->feature_y[j] = 
 					cell->cell_y * worley->cell_size + 
 					seed % worley->cell_size;

libvips/include/vips/util.h

@@ -328,6 +328,9 @@ void vips__change_suffix( const char *name, char *out, int mx,
 
 char *vips_realpath( const char *path );
 
+guint32 vips__random( guint32 seed );
+guint32 vips__random_add( guint32 seed, int value );
+
 #ifdef __cplusplus
 }
 #endif /*__cplusplus*/

libvips/iofuncs/util.c

@@ -1912,3 +1912,20 @@ vips_realpath( const char *path )
 
 	return( real );
 }
+
+/* A very simple random number generator. See:
+ * http://isthe.com/chongo/tech/comp/fnv/#FNV-source
+ */
+guint32
+vips__random( guint32 seed )
+{
+	return( 1103515245u * seed + 12345 );
+}
+
+guint32 
+vips__random_add( guint32 seed, int value )
+{
+	seed = ((2166136261u ^ seed) * 16777619u) ^ value;
+
+	return( vips__random( seed ) ); 
+}