Cycles: Refactor how we pass bounce info to light path node.

This commit changes the way how we pass bounce information to the Light
Path node. Instead of manualy copying the bounces into ShaderData, we now
directly pass PathState. This reduces the arguments that we need to pass
around and also makes it easier to extend the feature.

This commit also exposes the Transmission Bounce Depth to the Light Path
node. It works similar to the Transparent Depth Output: Replace a
Transmission lightpath after X bounces with another shader, e.g a Diffuse
one. This can be used to avoid black surfaces, due to low amount of max
bounces.

Reviewed by Sergey and Brecht, thanks for some hlp with this.

I tested compilation and usage on CPU (SVM and OSL), CUDA, OpenCL Split
and Mega kernel. Hopefully this covers all devices. :)

4 files changed, 28 insertions, 18 deletions

diff --git a/intern/cycles/kernel/osl/osl_services.cpp b/intern/cycles/kernel/osl/osl_services.cpp
index 8838c28ca13..0595282af64 100644
--- a/intern/cycles/kernel/osl/osl_services.cpp
+++ b/intern/cycles/kernel/osl/osl_services.cpp
@@ -101,6 +101,7 @@ ustring OSLRenderServices::u_curve_tangent_normal("geom:curve_tangent_normal");
 ustring OSLRenderServices::u_path_ray_length("path:ray_length");
 ustring OSLRenderServices::u_path_ray_depth("path:ray_depth");
 ustring OSLRenderServices::u_path_transparent_depth("path:transparent_depth");
+ustring OSLRenderServices::u_path_transmission_depth("path:transmission_depth");
 ustring OSLRenderServices::u_trace("trace");
 ustring OSLRenderServices::u_hit("hit");
 ustring OSLRenderServices::u_hitdist("hitdist");
@@ -726,12 +727,20 @@ bool OSLRenderServices::get_background_attribute(KernelGlobals *kg, ShaderData *
 	}
 	else if(name == u_path_ray_depth) {
 		/* Ray Depth */
-		int f = sd->ray_depth;
+		PathState *state = sd->osl_path_state;
+		int f = state->bounce;
 		return set_attribute_int(f, type, derivatives, val);
 	}
 	else if(name == u_path_transparent_depth) {
 		/* Transparent Ray Depth */
-		int f = sd->transparent_depth;
+		PathState *state = sd->osl_path_state;
+		int f = state->transparent_bounce;
+		return set_attribute_int(f, type, derivatives, val);
+	}
+	else if(name == u_path_transmission_depth) {
+		/* Transmission Ray Depth */
+		PathState *state = sd->osl_path_state;
+		int f = state->transmission_bounce;
 		return set_attribute_int(f, type, derivatives, val);
 	}
 	else if(name == u_ndc) {
@@ -1257,11 +1266,7 @@ bool OSLRenderServices::getmessage(OSL::ShaderGlobals *sg, ustring source, ustri
 
 				if(!tracedata->setup) {
 					/* lazy shader data setup */
-					ShaderData *original_sd = (ShaderData *)(sg->renderstate);
-					int bounce = original_sd->ray_depth + 1;
-					int transparent_bounce = original_sd->transparent_depth;
-
-					shader_setup_from_ray(kg, sd, &tracedata->isect, &tracedata->ray, bounce, transparent_bounce);
+					shader_setup_from_ray(kg, sd, &tracedata->isect, &tracedata->ray);
 					tracedata->setup = true;
 				}
 
diff --git a/intern/cycles/kernel/osl/osl_services.h b/intern/cycles/kernel/osl/osl_services.h
index f35ddcaef91..1d2f1556c3b 100644
--- a/intern/cycles/kernel/osl/osl_services.h
+++ b/intern/cycles/kernel/osl/osl_services.h
@@ -170,6 +170,7 @@ public:
 	static ustring u_path_ray_length;
 	static ustring u_path_ray_depth;
 	static ustring u_path_transparent_depth;
+	static ustring u_path_transmission_depth;
 	static ustring u_trace;
 	static ustring u_hit;
 	static ustring u_hitdist;
diff --git a/intern/cycles/kernel/osl/osl_shader.cpp b/intern/cycles/kernel/osl/osl_shader.cpp
index 2f234aa25ea..950786ab213 100644
--- a/intern/cycles/kernel/osl/osl_shader.cpp
+++ b/intern/cycles/kernel/osl/osl_shader.cpp
@@ -92,7 +92,7 @@ void OSLShader::thread_free(KernelGlobals *kg)
 
 /* Globals */
 
-static void shaderdata_to_shaderglobals(KernelGlobals *kg, ShaderData *sd,
+static void shaderdata_to_shaderglobals(KernelGlobals *kg, ShaderData *sd, PathState *state,
                                         int path_flag, OSLThreadData *tdata)
 {
 	OSL::ShaderGlobals *globals = &tdata->globals;
@@ -136,6 +136,7 @@ static void shaderdata_to_shaderglobals(KernelGlobals *kg, ShaderData *sd,
 
 	/* used by renderservices */
 	sd->osl_globals = kg;
+	sd->osl_path_state = state;
 }
 
 /* Surface */
@@ -317,11 +318,11 @@ static void flatten_surface_closure_tree(ShaderData *sd, int path_flag,
 	}
 }
 
-void OSLShader::eval_surface(KernelGlobals *kg, ShaderData *sd, int path_flag, ShaderContext ctx)
+void OSLShader::eval_surface(KernelGlobals *kg, ShaderData *sd, PathState *state, int path_flag, ShaderContext ctx)
 {
 	/* setup shader globals from shader data */
 	OSLThreadData *tdata = kg->osl_tdata;
-	shaderdata_to_shaderglobals(kg, sd, path_flag, tdata);
+	shaderdata_to_shaderglobals(kg, sd, state, path_flag, tdata);
 
 	/* execute shader for this point */
 	OSL::ShadingSystem *ss = (OSL::ShadingSystem*)kg->osl_ss;
@@ -377,11 +378,11 @@ static float3 flatten_background_closure_tree(const OSL::ClosureColor *closure)
 	return make_float3(0.0f, 0.0f, 0.0f);
 }
 
-float3 OSLShader::eval_background(KernelGlobals *kg, ShaderData *sd, int path_flag, ShaderContext ctx)
+float3 OSLShader::eval_background(KernelGlobals *kg, ShaderData *sd, PathState *state, int path_flag, ShaderContext ctx)
 {
 	/* setup shader globals from shader data */
 	OSLThreadData *tdata = kg->osl_tdata;
-	shaderdata_to_shaderglobals(kg, sd, path_flag, tdata);
+	shaderdata_to_shaderglobals(kg, sd, state, path_flag, tdata);
 
 	/* execute shader for this point */
 	OSL::ShadingSystem *ss = (OSL::ShadingSystem*)kg->osl_ss;
@@ -486,11 +487,11 @@ static void flatten_volume_closure_tree(ShaderData *sd,
 	}
 }
 
-void OSLShader::eval_volume(KernelGlobals *kg, ShaderData *sd, int path_flag, ShaderContext ctx)
+void OSLShader::eval_volume(KernelGlobals *kg, ShaderData *sd, PathState *state, int path_flag, ShaderContext ctx)
 {
 	/* setup shader globals from shader data */
 	OSLThreadData *tdata = kg->osl_tdata;
-	shaderdata_to_shaderglobals(kg, sd, path_flag, tdata);
+	shaderdata_to_shaderglobals(kg, sd, state, path_flag, tdata);
 
 	/* execute shader */
 	OSL::ShadingSystem *ss = (OSL::ShadingSystem*)kg->osl_ss;
@@ -512,7 +513,10 @@ void OSLShader::eval_displacement(KernelGlobals *kg, ShaderData *sd, ShaderConte
 {
 	/* setup shader globals from shader data */
 	OSLThreadData *tdata = kg->osl_tdata;
-	shaderdata_to_shaderglobals(kg, sd, 0, tdata);
+
+	PathState state = {0};
+
+	shaderdata_to_shaderglobals(kg, sd, &state, 0, tdata);
 
 	/* execute shader */
 	OSL::ShadingSystem *ss = (OSL::ShadingSystem*)kg->osl_ss;
diff --git a/intern/cycles/kernel/osl/osl_shader.h b/intern/cycles/kernel/osl/osl_shader.h
index 15dd74f9d38..7d26cd40da5 100644
--- a/intern/cycles/kernel/osl/osl_shader.h
+++ b/intern/cycles/kernel/osl/osl_shader.h
@@ -53,9 +53,9 @@ public:
 	static void thread_free(KernelGlobals *kg);
 
 	/* eval */
-	static void eval_surface(KernelGlobals *kg, ShaderData *sd, int path_flag, ShaderContext ctx);
-	static float3 eval_background(KernelGlobals *kg, ShaderData *sd, int path_flag, ShaderContext ctx);
-	static void eval_volume(KernelGlobals *kg, ShaderData *sd, int path_flag, ShaderContext ctx);
+	static void eval_surface(KernelGlobals *kg, ShaderData *sd, PathState *state, int path_flag, ShaderContext ctx);
+	static float3 eval_background(KernelGlobals *kg, ShaderData *sd, PathState *state, int path_flag, ShaderContext ctx);
+	static void eval_volume(KernelGlobals *kg, ShaderData *sd, PathState *state, int path_flag, ShaderContext ctx);
 	static void eval_displacement(KernelGlobals *kg, ShaderData *sd, ShaderContext ctx);
 
 	/* sample & eval */