Fix T42139, vertical noise stripe patterns in noise texture.

Two fixes here (only the second one is strictly needed to fix the issue,
but both make the system better).

First is introduction of a random generator array for use with threaded
systems where each thread needs to access its own number generator.
The random texture now uses this so it should not be influenced by other
random generator reseedings of the main random generator like it did
before.

Second, I reshuffled the texture code to resample the upper bits of the
random number first. According to Numerical Recipes, this is where the
most variance can be found, so by sampling those we avoid correlation
issues. Also, multiplying here is not ideal because if a pair of bits
are zero, then the whole result will also be zero.

Overall this is much more random (tm) than before, however result will
also be brighter, since we now have less black spots. Tweaking the
brightness/contrast should somewhat fix that, generally having the same
result as before is not possible anyway if we are to really fix this.

Also, seems like exposing procedural depth might be nice here since it
influences the precision of the texture lookup.

2 files changed, 25 insertions, 8 deletions

diff --git a/source/blender/render/extern/include/RE_render_ext.h b/source/blender/render/extern/include/RE_render_ext.h
index eb861d440d8..6d083ec785d 100644
--- a/source/blender/render/extern/include/RE_render_ext.h
+++ b/source/blender/render/extern/include/RE_render_ext.h
@@ -61,5 +61,7 @@ void RE_free_sample_material(struct Material *mat);
 void RE_sample_material_color(struct Material *mat, float color[3], float *alpha, const float volume_co[3], const float surface_co[3],
                               int face_index, short hit_quad, struct DerivedMesh *orcoDm, struct Object *ob);
 
+void RE_init_texture_rng(void);
+void RE_exit_texture_rng(void);
 #endif /* __RE_RENDER_EXT_H__ */
 
diff --git a/source/blender/render/intern/source/render_texture.c b/source/blender/render/intern/source/render_texture.c
index 0e61c3e796a..14e84c4fca9 100644
--- a/source/blender/render/intern/source/render_texture.c
+++ b/source/blender/render/intern/source/render_texture.c
@@ -85,8 +85,19 @@
 extern struct Render R;
 /* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
 
+static RNG_THREAD_ARRAY *random_tex_array;
 
 
+void RE_init_texture_rng()
+{
+	random_tex_array = BLI_rng_threaded_new();
+}
+
+void RE_exit_texture_rng()
+{
+	BLI_rng_threaded_free(random_tex_array);
+}
+
 
 static void init_render_texture(Render *re, Tex *tex)
 {
@@ -709,19 +720,23 @@ static float voronoiTex(Tex *tex, const float texvec[3], TexResult *texres)
 
 /* ------------------------------------------------------------------------- */
 
-static int texnoise(Tex *tex, TexResult *texres)
+static int texnoise(Tex *tex, TexResult *texres, int thread)
 {
 	float div=3.0;
-	int val, ran, loop;
+	int val, ran, loop, shift = 30;
 	
-	ran= BLI_rand();
-	val= (ran & 3);
+	ran=  BLI_rng_thread_rand(random_tex_array, thread);
 	
 	loop= tex->noisedepth;
+
+	/* start from top bits since they have more variance */
+	val= ((ran >> shift) & 3);
+	shift -= 2;
+	
 	while (loop--) {
-		ran= (ran>>2);
-		val*= (ran & 3);
-		div*= 3.0f;
+		val += ((ran >> shift) & 3);
+		div += 3.0f;
+		shift -= 2;		
 	}
 	
 	texres->tin= ((float)val)/div;
@@ -1127,7 +1142,7 @@ static int multitex(Tex *tex, float texvec[3], float dxt[3], float dyt[3], int o
 				retval = stucci(tex, texvec, texres);
 				break;
 			case TEX_NOISE:
-				retval = texnoise(tex, texres);
+				retval = texnoise(tex, texres, thread);
 				break;
 			case TEX_IMAGE:
 				if (osatex) retval = imagewraposa(tex, tex->ima, NULL, texvec, dxt, dyt, texres, pool);