Strange behavior of Cycles Brick Texture #46030

New Issue

Martin Leurs · 2015-09-06T17:30:56+02:00

Martin Leurs commented

2015-09-06 17:30:56 +02:00

Windows 7
Blender 2.75

If I add a Brick Texture in a Cycles Material, the row of bricks on the bottom does not lookas random generated then the other rows. All of the other rows seam to contain randomly choosen brick colors but in the row on the bottom, the bricks look more like colord with a color band.

I hope this gets clearer with an image:

And the blend file:
brick_texture_not_random.blend

Best regards
Martin

Windows 7 Blender 2.75 If I add a Brick Texture in a Cycles Material, the row of bricks on the bottom does not lookas random generated then the other rows. All of the other rows seam to contain randomly choosen brick colors but in the row on the bottom, the bricks look more like colord with a color band. I hope this gets clearer with an image: ![brick_texture_not_random.jpg](https://archive.blender.org/developer/F230849/brick_texture_not_random.jpg) And the blend file: [brick_texture_not_random.blend](https://archive.blender.org/developer/F230851/brick_texture_not_random.blend) Best regards Martin

Martin Leurs commented

2015-09-06 17:30:56 +02:00

Changed status to: 'Open'

Martin Leurs commented

2015-09-06 17:30:56 +02:00

Added subscriber: @martinleurs

Sergey Sharybin self-assigned this 2015-09-07 08:52:59 +02:00

Sergey Sharybin commented

2015-09-07 12:58:49 +02:00

Developer note: the issue is caused by poor distribution of random numbers coming from noise() with n close to zero. We can either simply offset n by 1024 (or xor it with some mask) or can simply re-use CMJ's hash, like this P257: Fix for #46030

diff --git a/intern/cycles/kernel/svm/svm_brick.h b/intern/cycles/kernel/svm/svm_brick.h
index fcf8f47..85647d5 100644
--- a/intern/cycles/kernel/svm/svm_brick.h
+++ b/intern/cycles/kernel/svm/svm_brick.h
@@ -18,12 +18,9 @@ CCL_NAMESPACE_BEGIN
 
 /* Brick */
 
-ccl_device_noinline float brick_noise(int n) /* fast integer noise */
+ccl_device_inline float brick_noise(int n)
 {
-	int nn;
-	n = (n >> 13) ^ n;
-	nn = (n * (n * n * 60493 + 19990303) + 1376312589) & 0x7fffffff;
-	return 0.5f * ((float)nn / 1073741824.0f);
+	return cmj_randfloat(n, 0xbcd60b1e);
 }
 
 ccl_device_noinline float2 svm_brick(float3 p, float mortar_size, float bias,

In any case this will change distribution of brick colors which we probably better to avoid at this point.

Developer note: the issue is caused by poor distribution of random numbers coming from `noise()` with `n` close to zero. We can either simply offset `n` by 1024 (or xor it with some mask) or can simply re-use CMJ's hash, like this [P257: Fix for #46030](https://archive.blender.org/developer/P257.txt) ```diff diff --git a/intern/cycles/kernel/svm/svm_brick.h b/intern/cycles/kernel/svm/svm_brick.h index fcf8f47..85647d5 100644 --- a/intern/cycles/kernel/svm/svm_brick.h +++ b/intern/cycles/kernel/svm/svm_brick.h @@ -18,12 +18,9 @@ CCL_NAMESPACE_BEGIN /* Brick */ -ccl_device_noinline float brick_noise(int n) /* fast integer noise */ +ccl_device_inline float brick_noise(int n) { - int nn; - n = (n >> 13) ^ n; - nn = (n * (n * n * 60493 + 19990303) + 1376312589) & 0x7fffffff; - return 0.5f * ((float)nn / 1073741824.0f); + return cmj_randfloat(n, 0xbcd60b1e); } ccl_device_noinline float2 svm_brick(float3 p, float mortar_size, float bias, ``` In any case this will change distribution of brick colors which we probably better to avoid at this point.

Thomas Dinges commented

2015-09-08 22:08:57 +02:00

Added subscriber: @ThomasDinges