[Bf-blender-cvs] [a0d7db5] master: Cycles: Small tweaks for Henyey Greenstein closure code.

[Thomas Dinges]

Commit: a0d7db503d82c1a5b56a5723da90364f11569b37
Author: Thomas Dinges
Date:   Tue Feb 17 17:44:32 2015 +0100
Branches: master
https://developer.blender.org/rBa0d7db503d82c1a5b56a5723da90364f11569b37

Cycles: Small tweaks for Henyey Greenstein closure code.

* Avoid duplicative fabs(g) check in sample code.
* Avoid dot product in eval code.

Helps like ~1% when Scatter Anisotropy is 0.

===================================================================

M       intern/cycles/kernel/closure/volume.h
M       intern/cycles/kernel/svm/svm_closure.h

===================================================================

diff --git a/intern/cycles/kernel/closure/volume.h 
b/intern/cycles/kernel/closure/volume.h
index 9f519e2..1cf5e17 100644
--- a/intern/cycles/kernel/closure/volume.h
+++ b/intern/cycles/kernel/closure/volume.h
@@ -26,9 +26,6 @@ CCL_NAMESPACE_BEGIN
  * uniform sphere. g=0 uniform diffuse-like, g=1 close to sharp single ray. */
 ccl_device float single_peaked_henyey_greenstein(float cos_theta, float g)
 {
-       if(fabsf(g) < 1e-3f)
-               return M_1_PI_F * 0.25f;
-       
        return ((1.0f - g * g) / safe_powf(1.0f + g * g - 2.0f * g * cos_theta, 
1.5f)) * (M_1_PI_F * 0.25f);
 };
 
@@ -47,9 +44,13 @@ ccl_device float3 volume_henyey_greenstein_eval_phase(const 
ShaderClosure *sc, c
        float g = sc->data0;
 
        /* note that I points towards the viewer */
-       float cos_theta = dot(-I, omega_in);
-
-       *pdf = single_peaked_henyey_greenstein(cos_theta, g);
+       if(fabsf(g) < 1e-3f) {
+               *pdf = M_1_PI_F * 0.25f;
+       }
+       else {
+               float cos_theta = dot(-I, omega_in);
+               *pdf = single_peaked_henyey_greenstein(cos_theta, g);
+       }
 
        return make_float3(*pdf, *pdf, *pdf);
 }
@@ -63,10 +64,12 @@ ccl_device int volume_henyey_greenstein_sample(const 
ShaderClosure *sc, float3 I
        /* match pdf for small g */
        if(fabsf(g) < 1e-3f) {
                cos_theta = (1.0f - 2.0f * randu);
+               *pdf = M_1_PI_F * 0.25f;
        }
        else {
                float k = (1.0f - g * g) / (1.0f - g + 2.0f * g * randu);
                cos_theta = (1.0f + g * g - k * k) / (2.0f * g);
+               *pdf = single_peaked_henyey_greenstein(cos_theta, g);
        }
 
        float sin_theta = safe_sqrtf(1.0f - cos_theta * cos_theta);
@@ -80,7 +83,6 @@ ccl_device int volume_henyey_greenstein_sample(const 
ShaderClosure *sc, float3 I
        make_orthonormals(-I, &T, &B);
        *omega_in = sin_theta * cos_phi * T + sin_theta * sin_phi * B + 
cos_theta * (-I);
 
-       *pdf = single_peaked_henyey_greenstein(cos_theta, g);
        *eval = make_float3(*pdf, *pdf, *pdf); /* perfect importance sampling */
 
 #ifdef __RAY_DIFFERENTIALS__
diff --git a/intern/cycles/kernel/svm/svm_closure.h 
b/intern/cycles/kernel/svm/svm_closure.h
index ed3f277..07ac710 100644
--- a/intern/cycles/kernel/svm/svm_closure.h
+++ b/intern/cycles/kernel/svm/svm_closure.h
@@ -528,8 +528,7 @@ ccl_device void svm_node_closure_volume(KernelGlobals *kg, 
ShaderData *sd, float
                        ShaderClosure *sc = svm_node_closure_get_bsdf(sd, 
mix_weight * density);
 
                        if(sc) {
-                               float g = param2;
-                               sc->data0 = g;
+                               sc->data0 = param2; /* g */
                                sd->flag |= volume_henyey_greenstein_setup(sc);
                        }
                        break;

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