Cycles Volume Render: work on nodes and closures.

* Henyey-Greenstein scattering closure implementation.
* Rename transparent to absorption node and isotropic to scatter node.
* Volume density is folded into the closure weights.
* OSL support for volume closures and nodes.
* This commit has no user visible changes, there is no volume render code yet.

This is work by "storm", Stuart Broadfoot, Thomas Dinges and myself.

1 files changed, 91 insertions, 23 deletions

diff --git a/intern/cycles/kernel/closure/volume.h b/intern/cycles/kernel/closure/volume.h
index f4932568c1f..dae24fb03fd 100644
--- a/intern/cycles/kernel/closure/volume.h
+++ b/intern/cycles/kernel/closure/volume.h
@@ -14,53 +14,102 @@
  * limitations under the License
  */
 
+#ifndef __VOLUME_H__
+#define __VOLUME_H__
+
 CCL_NAMESPACE_BEGIN
 
-/* note: the interfaces here are just as an example, need to figure
- * out the right functions and parameters to use */
+/* HENYEY-GREENSTEIN CLOSURE */
 
-/* ISOTROPIC VOLUME CLOSURE */
+/* Given cosine between rays, return probability density that a photon bounces
+ * to that direction. The g parameter controls how different it is from the
+ * 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);
+};
 
-ccl_device int volume_isotropic_setup(ShaderClosure *sc, float density)
+ccl_device int volume_henyey_greenstein_setup(ShaderClosure *sc)
 {
-	sc->type = CLOSURE_VOLUME_ISOTROPIC_ID;
-	sc->data0 = density;
+	sc->type = CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID;
+	
+	/* clamp anisotropy to avoid delta function */
+	sc->data0 = signf(sc->data0) * min(fabsf(sc->data0), 1.0f - 1e-3f);
 
-	return SD_VOLUME;
+	return SD_BSDF|SD_BSDF_HAS_EVAL;
 }
 
-ccl_device float3 volume_isotropic_eval_phase(const ShaderClosure *sc, const float3 omega_in, const float3 omega_out)
+ccl_device float3 volume_henyey_greenstein_eval_phase(const ShaderClosure *sc, const float3 I, float3 omega_in, float *pdf)
 {
-	return make_float3(1.0f, 1.0f, 1.0f);
-}
+	float g = sc->data0;
 
-/* TRANSPARENT VOLUME CLOSURE */
+	/* note that I points towards the viewer */
+	float cos_theta = dot(-I, omega_in);
 
-ccl_device int volume_transparent_setup(ShaderClosure *sc, float density)
+	*pdf = single_peaked_henyey_greenstein(cos_theta, g);
+
+	return make_float3(*pdf, *pdf, *pdf);
+}
+
+ccl_device int volume_henyey_greenstein_sample(const ShaderClosure *sc, float3 I, float3 dIdx, float3 dIdy, float randu, float randv,
+	float3 *eval, float3 *omega_in, float3 *domega_in_dx, float3 *domega_in_dy, float *pdf)
 {
-	sc->type = CLOSURE_VOLUME_TRANSPARENT_ID;
-	sc->data0 = density;
+	float g = sc->data0;
+	float cos_phi, sin_phi, cos_theta;
 
-	return SD_VOLUME;
+	/* match pdf for small g */
+	if(fabsf(g) < 1e-3f) {
+		cos_theta = (1.0f - 2.0f * randu);
+	}
+	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);
+	}
+
+	float sin_theta = safe_sqrtf(1.0f - cos_theta * cos_theta);
+
+	float phi = M_2PI_F * randv;
+	cos_phi = cosf(phi);
+	sin_phi = sinf(phi);
+
+	/* note that I points towards the viewer and so is used negated */
+	float3 T, B;
+	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__
+	/* todo: implement ray differential estimation */
+	*domega_in_dx = make_float3(0.0f, 0.0f, 0.0f);
+	*domega_in_dy = make_float3(0.0f, 0.0f, 0.0f);
+#endif
+
+	return LABEL_VOLUME_SCATTER;
 }
 
-ccl_device float3 volume_transparent_eval_phase(const ShaderClosure *sc, const float3 omega_in, const float3 omega_out)
+/* ABSORPTION VOLUME CLOSURE */
+
+ccl_device int volume_absorption_setup(ShaderClosure *sc)
 {
-	return make_float3(1.0f, 1.0f, 1.0f);
+	sc->type = CLOSURE_VOLUME_ABSORPTION_ID;
+
+	return SD_VOLUME;
 }
 
 /* VOLUME CLOSURE */
 
-ccl_device float3 volume_eval_phase(KernelGlobals *kg, const ShaderClosure *sc, const float3 omega_in, const float3 omega_out)
+ccl_device float3 volume_eval_phase(const ShaderClosure *sc, const float3 I, float3 omega_in, float *pdf)
 {
 	float3 eval;
 
 	switch(sc->type) {
-		case CLOSURE_VOLUME_ISOTROPIC_ID:
-			eval = volume_isotropic_eval_phase(sc, omega_in, omega_out);
-			break;
-		case CLOSURE_VOLUME_TRANSPARENT_ID:
-			eval = volume_transparent_eval_phase(sc, omega_in, omega_out);
+		case CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID:
+			eval = volume_henyey_greenstein_eval_phase(sc, I, omega_in, pdf);
 			break;
 		default:
 			eval = make_float3(0.0f, 0.0f, 0.0f);
@@ -70,5 +119,24 @@ ccl_device float3 volume_eval_phase(KernelGlobals *kg, const ShaderClosure *sc,
 	return eval;
 }
 
+ccl_device int volume_sample(const ShaderData *sd, const ShaderClosure *sc, float randu,
+	float randv, float3 *eval, float3 *omega_in, differential3 *domega_in, float *pdf)
+{
+	int label;
+
+	switch(sc->type) {
+		case CLOSURE_VOLUME_HENYEY_GREENSTEIN_ID:
+			label = volume_henyey_greenstein_sample(sc, sd->I, sd->dI.dx, sd->dI.dy, randu, randv, eval, omega_in, &domega_in->dx, &domega_in->dy, pdf);
+			break;
+		default:
+			*eval = make_float3(0.0f, 0.0f, 0.0f);
+			label = LABEL_NONE;
+			break;
+	}
+
+	return label;
+}
+
 CCL_NAMESPACE_END
 
+#endif