/*
 * Copyright 2011-2013 Blender Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

CCL_NAMESPACE_BEGIN

#ifdef __BRANCHED_PATH__

ccl_device_inline void kernel_branched_path_ao(KernelGlobals *kg,
                                               ShaderData *sd,
                                               ShaderData *emission_sd,
                                               PathRadiance *L,
                                               ccl_addr_space PathState *state,
                                               float3 throughput)
{
	int num_samples = kernel_data.integrator.ao_samples;
	float num_samples_inv = 1.0f/num_samples;
	float ao_factor = kernel_data.background.ao_factor;
	float3 ao_N;
	float3 ao_bsdf = shader_bsdf_ao(kg, sd, ao_factor, &ao_N);
	float3 ao_alpha = shader_bsdf_alpha(kg, sd);

	for(int j = 0; j < num_samples; j++) {
		float bsdf_u, bsdf_v;
		path_branched_rng_2D(kg, state->rng_hash, state, j, num_samples, PRNG_BSDF_U, &bsdf_u, &bsdf_v);

		float3 ao_D;
		float ao_pdf;

		sample_cos_hemisphere(ao_N, bsdf_u, bsdf_v, &ao_D, &ao_pdf);

		if(dot(sd->Ng, ao_D) > 0.0f && ao_pdf != 0.0f) {
			Ray light_ray;
			float3 ao_shadow;

			light_ray.P = ray_offset(sd->P, sd->Ng);
			light_ray.D = ao_D;
			light_ray.t = kernel_data.background.ao_distance;
			light_ray.time = sd->time;
			light_ray.dP = sd->dP;
			light_ray.dD = differential3_zero();

			if(!shadow_blocked(kg, sd, emission_sd, state, &light_ray, &ao_shadow)) {
				path_radiance_accum_ao(L, state, throughput*num_samples_inv, ao_alpha, ao_bsdf, ao_shadow);
			}
			else {
				path_radiance_accum_total_ao(L, state, throughput*num_samples_inv, ao_bsdf);
			}
		}
	}
}

#ifndef __SPLIT_KERNEL__

#ifdef __VOLUME__
ccl_device_forceinline void kernel_branched_path_volume(
	KernelGlobals *kg,
	ShaderData *sd,
	PathState *state,
	Ray *ray,
	float3 *throughput,
	ccl_addr_space Intersection *isect,
	bool hit,
	ShaderData *indirect_sd,
	ShaderData *emission_sd,
	PathRadiance *L)
{
	/* Sanitize volume stack. */
	if(!hit) {
		kernel_volume_clean_stack(kg, state->volume_stack);
	}

	if(state->volume_stack[0].shader == SHADER_NONE) {
		return;
	}

	/* volume attenuation, emission, scatter */
	Ray volume_ray = *ray;
	volume_ray.t = (hit)? isect->t: FLT_MAX;

	bool heterogeneous = volume_stack_is_heterogeneous(kg, state->volume_stack);

#  ifdef __VOLUME_DECOUPLED__
	/* decoupled ray marching only supported on CPU */
	if(kernel_data.integrator.volume_decoupled) {
		/* cache steps along volume for repeated sampling */
		VolumeSegment volume_segment;

		shader_setup_from_volume(kg, sd, &volume_ray);
		kernel_volume_decoupled_record(kg, state,
			&volume_ray, sd, &volume_segment, heterogeneous);

		/* direct light sampling */
		if(volume_segment.closure_flag & SD_SCATTER) {
			volume_segment.sampling_method = volume_stack_sampling_method(kg, state->volume_stack);

			int all = kernel_data.integrator.sample_all_lights_direct;

			kernel_branched_path_volume_connect_light(kg, sd,
				emission_sd, *throughput, state, L, all,
				&volume_ray, &volume_segment);

			/* indirect light sampling */
			int num_samples = kernel_data.integrator.volume_samples;
			float num_samples_inv = 1.0f/num_samples;

			for(int j = 0; j < num_samples; j++) {
				PathState ps = *state;
				Ray pray = *ray;
				float3 tp = *throughput;

				/* branch RNG state */
				path_state_branch(&ps, j, num_samples);

				/* scatter sample. if we use distance sampling and take just one
				 * sample for direct and indirect light, we could share this
				 * computation, but makes code a bit complex */
				float rphase = path_state_rng_1D(kg, &ps, PRNG_PHASE_CHANNEL);
				float rscatter = path_state_rng_1D(kg, &ps, PRNG_SCATTER_DISTANCE);

				VolumeIntegrateResult result = kernel_volume_decoupled_scatter(kg,
					&ps, &pray, sd, &tp, rphase, rscatter, &volume_segment, NULL, false);

				if(result == VOLUME_PATH_SCATTERED &&
				   kernel_path_volume_bounce(kg,
				                             sd,
				                             &tp,
				                             &ps,
				                             &L->state,
				                             &pray))
				{
					kernel_path_indirect(kg,
					                     indirect_sd,
					                     emission_sd,
					                     &pray,
					                     tp*num_samples_inv,
					                     &ps,
					                     L);

					/* for render passes, sum and reset indirect light pass variables
					 * for the next samples */
					path_radiance_sum_indirect(L);
					path_radiance_reset_indirect(L);
				}
			}
		}

		/* emission and transmittance */
		if(volume_segment.closure_flag & SD_EMISSION)
			path_radiance_accum_emission(L, state, *throughput, volume_segment.accum_emission);
		*throughput *= volume_segment.accum_transmittance;

		/* free cached steps */
		kernel_volume_decoupled_free(kg, &volume_segment);
	}
	else
#  endif  /* __VOLUME_DECOUPLED__ */
	{
		/* GPU: no decoupled ray marching, scatter probalistically */
		int num_samples = kernel_data.integrator.volume_samples;
		float num_samples_inv = 1.0f/num_samples;

		/* todo: we should cache the shader evaluations from stepping
		 * through the volume, for now we redo them multiple times */

		for(int j = 0; j < num_samples; j++) {
			PathState ps = *state;
			Ray pray = *ray;
			float3 tp = (*throughput) * num_samples_inv;

			/* branch RNG state */
			path_state_branch(&ps, j, num_samples);

			VolumeIntegrateResult result = kernel_volume_integrate(
				kg, &ps, sd, &volume_ray, L, &tp, heterogeneous);

#  ifdef __VOLUME_SCATTER__
			if(result == VOLUME_PATH_SCATTERED) {
				/* todo: support equiangular, MIS and all light sampling.
				 * alternatively get decoupled ray marching working on the GPU */
				kernel_path_volume_connect_light(kg, sd, emission_sd, tp, state, L);

				if(kernel_path_volume_bounce(kg,
				                             sd,
				                             &tp,
				                             &ps,
				                             &L->state,
				                             &pray))
				{
					kernel_path_indirect(kg,
					                     indirect_sd,
					                     emission_sd,
					                     &pray,
					                     tp,
					                     &ps,
					                     L);

					/* for render passes, sum and reset indirect light pass variables
					 * for the next samples */
					path_radiance_sum_indirect(L);
					path_radiance_reset_indirect(L);
				}
			}
# endif  /* __VOLUME_SCATTER__ */
		}

		/* todo: avoid this calculation using decoupled ray marching */
		kernel_volume_shadow(kg, emission_sd, state, &volume_ray, throughput);
	}
}
#endif  /* __VOLUME__ */

/* bounce off surface and integrate indirect light */
ccl_device_noinline void kernel_branched_path_surface_indirect_light(KernelGlobals *kg,
	ShaderData *sd, ShaderData *indirect_sd, ShaderData *emission_sd,
	float3 throughput, float num_samples_adjust, PathState *state, PathRadiance *L)
{
	float sum_sample_weight = 0.0f;
#ifdef __DENOISING_FEATURES__
	if(state->denoising_feature_weight > 0.0f) {
		for(int i = 0; i < sd->num_closure; i++) {
			const ShaderClosure *sc = &sd->closure[i];

			/* transparency is not handled here, but in outer loop */
			if(!CLOSURE_IS_BSDF(sc->type) || CLOSURE_IS_BSDF_TRANSPARENT(sc->type)) {
				continue;
			}

			sum_sample_weight += sc->sample_weight;
		}
	}
	else {
		sum_sample_weight = 1.0f;
	}
#endif  /* __DENOISING_FEATURES__ */

	for(int i = 0; i < sd->num_closure; i++) {
		const ShaderClosure *sc = &sd->closure[i];

		/* transparency is not handled here, but in outer loop */
		if(!CLOSURE_IS_BSDF(sc->type) || CLOSURE_IS_BSDF_TRANSPARENT(sc->type)) {
			continue;
		}

		int num_samples;

		if(CLOSURE_IS_BSDF_DIFFUSE(sc->type))
			num_samples = kernel_data.integrator.diffuse_samples;
		else if(CLOSURE_IS_BSDF_BSSRDF(sc->type))
			num_samples = 1;
		else if(CLOSURE_IS_BSDF_GLOSSY(sc->type))
			num_samples = kernel_data.integrator.glossy_samples;
		else
			num_samples = kernel_data.integrator.transmission_samples;

		num_samples = ceil_to_int(num_samples_adjust*num_samples);

		float num_samples_inv = num_samples_adjust/num_samples;

		for(int j = 0; j < num_samples; j++) {
			PathState ps = *state;
			float3 tp = throughput;
			Ray bsdf_ray;
#ifdef __SHADOW_TRICKS__
			float shadow_transparency = L->shadow_transparency;
#endif

			ps.rng_hash = cmj_hash(state->rng_hash, i);

			if(!kernel_branched_path_surface_bounce(kg,
			                                        sd,
			                                        sc,
			                                        j,
			                                        num_samples,
			                                        &tp,
			                                        &ps,
			                                        &L->state,
			                                        &bsdf_ray,
			                                        sum_sample_weight))
			{
				continue;
			}

			ps.rng_hash = state->rng_hash;

			kernel_path_indirect(kg,
			                     indirect_sd,
			                     emission_sd,
			                     &bsdf_ray,
			                     tp*num_samples_inv,
			                     &ps,
			                     L);

			/* for render passes, sum and reset indirect light pass variables
			 * for the next samples */
			path_radiance_sum_indirect(L);
			path_radiance_reset_indirect(L);

#ifdef __SHADOW_TRICKS__
			L->shadow_transparency = shadow_transparency;
#endif
		}
	}
}

#ifdef __SUBSURFACE__
ccl_device void kernel_branched_path_subsurface_scatter(KernelGlobals *kg,
                                                        ShaderData *sd,
                                                        ShaderData *indirect_sd,
                                                        ShaderData *emission_sd,
                                                        PathRadiance *L,
                                                        PathState *state,
                                                        Ray *ray,
                                                        float3 throughput)
{
	for(int i = 0; i < sd->num_closure; i++) {
		ShaderClosure *sc = &sd->closure[i];

		if(!CLOSURE_IS_BSSRDF(sc->type))
			continue;

		/* set up random number generator */
		uint lcg_state = lcg_state_init(state, 0x68bc21eb);
		int num_samples = kernel_data.integrator.subsurface_samples;
		float num_samples_inv = 1.0f/num_samples;
		uint bssrdf_rng_hash = cmj_hash(state->rng_hash, i);

		/* do subsurface scatter step with copy of shader data, this will
		 * replace the BSSRDF with a diffuse BSDF closure */
		for(int j = 0; j < num_samples; j++) {
			SubsurfaceIntersection ss_isect;
			float bssrdf_u, bssrdf_v;
			path_branched_rng_2D(kg, bssrdf_rng_hash, state, j, num_samples, PRNG_BSDF_U, &bssrdf_u, &bssrdf_v);
			int num_hits = subsurface_scatter_multi_intersect(kg,
			                                                  &ss_isect,
			                                                  sd,
			                                                  sc,
			                                                  &lcg_state,
			                                                  bssrdf_u, bssrdf_v,
			                                                  true);
#ifdef __VOLUME__
			Ray volume_ray = *ray;
			bool need_update_volume_stack =
			        kernel_data.integrator.use_volumes &&
			        sd->object_flag & SD_OBJECT_INTERSECTS_VOLUME;
#endif  /* __VOLUME__ */

			/* compute lighting with the BSDF closure */
			for(int hit = 0; hit < num_hits; hit++) {
				ShaderData bssrdf_sd = *sd;
				subsurface_scatter_multi_setup(kg,
				                               &ss_isect,
				                               hit,
				                               &bssrdf_sd,
				                               state,
				                               state->flag,
				                               sc,
				                               true);

				PathState hit_state = *state;

				path_state_branch(&hit_state, j, num_samples);

#ifdef __VOLUME__
				if(need_update_volume_stack) {
					/* Setup ray from previous surface point to the new one. */
					float3 P = ray_offset(bssrdf_sd.P, -bssrdf_sd.Ng);
					volume_ray.D = normalize_len(P - volume_ray.P,
					                             &volume_ray.t);

					kernel_volume_stack_update_for_subsurface(
					    kg,
					    emission_sd,
					    &volume_ray,
					    hit_state.volume_stack);
				}
#endif  /* __VOLUME__ */

#ifdef __EMISSION__
				/* direct light */
				if(kernel_data.integrator.use_direct_light) {
					int all = (kernel_data.integrator.sample_all_lights_direct) ||
					          (state->flag & PATH_RAY_SHADOW_CATCHER);
					kernel_branched_path_surface_connect_light(
					        kg,
					        &bssrdf_sd,
					        emission_sd,
					        &hit_state,
					        throughput,
					        num_samples_inv,
					        L,
					        all);
				}
#endif  /* __EMISSION__ */

				/* indirect light */
				kernel_branched_path_surface_indirect_light(
				        kg,
				        &bssrdf_sd,
				        indirect_sd,
				        emission_sd,
				        throughput,
				        num_samples_inv,
				        &hit_state,
				        L);
			}
		}
	}
}
#endif  /* __SUBSURFACE__ */

ccl_device void kernel_branched_path_integrate(KernelGlobals *kg,
                                               uint rng_hash,
                                               int sample,
                                               Ray ray,
                                               ccl_global float *buffer,
                                               PathRadiance *L)
{
	/* initialize */
	float3 throughput = make_float3(1.0f, 1.0f, 1.0f);

	path_radiance_init(L, kernel_data.film.use_light_pass);

	/* shader data memory used for both volumes and surfaces, saves stack space */
	ShaderData sd;
	/* shader data used by emission, shadows, volume stacks, indirect path */
	ShaderData emission_sd, indirect_sd;

	PathState state;
	path_state_init(kg, &emission_sd, &state, rng_hash, sample, &ray);

	/* Main Loop
	 * Here we only handle transparency intersections from the camera ray.
	 * Indirect bounces are handled in kernel_branched_path_surface_indirect_light().
	 */
	for(;;) {
		/* Find intersection with objects in scene. */
		Intersection isect;
		bool hit = kernel_path_scene_intersect(kg, &state, &ray, &isect, L);

#ifdef __VOLUME__
		/* Volume integration. */
		kernel_branched_path_volume(kg,
		                            &sd,
		                            &state,
		                            &ray,
		                            &throughput,
		                            &isect,
		                            hit,
		                            &indirect_sd,
		                            &emission_sd,
		                            L);
#endif  /* __VOLUME__ */

		/* Shade background. */
		if(!hit) {
			kernel_path_background(kg, &state, &ray, throughput, &emission_sd, L);
			break;
		}

		/* Setup and evaluate shader. */
		shader_setup_from_ray(kg, &sd, &isect, &ray);
		shader_eval_surface(kg, &sd, &state, state.flag);
		shader_merge_closures(&sd);

		/* Apply shadow catcher, holdout, emission. */
		if(!kernel_path_shader_apply(kg,
		                             &sd,
		                             &state,
		                             &ray,
		                             throughput,
		                             &emission_sd,
		                             L,
		                             buffer))
		{
			break;
		}

		/* transparency termination */
		if(state.flag & PATH_RAY_TRANSPARENT) {
			/* path termination. this is a strange place to put the termination, it's
			 * mainly due to the mixed in MIS that we use. gives too many unneeded
			 * shader evaluations, only need emission if we are going to terminate */
			float probability = path_state_continuation_probability(kg, &state, throughput);

			if(probability == 0.0f) {
				break;
			}
			else if(probability != 1.0f) {
				float terminate = path_state_rng_1D(kg, &state, PRNG_TERMINATE);

				if(terminate >= probability)
					break;

				throughput /= probability;
			}
		}

		kernel_update_denoising_features(kg, &sd, &state, L);

#ifdef __AO__
		/* ambient occlusion */
		if(kernel_data.integrator.use_ambient_occlusion || (sd.flag & SD_AO)) {
			kernel_branched_path_ao(kg, &sd, &emission_sd, L, &state, throughput);
		}
#endif  /* __AO__ */

#ifdef __SUBSURFACE__
		/* bssrdf scatter to a different location on the same object */
		if(sd.flag & SD_BSSRDF) {
			kernel_branched_path_subsurface_scatter(kg, &sd, &indirect_sd, &emission_sd,
			                                        L, &state, &ray, throughput);
		}
#endif  /* __SUBSURFACE__ */

		if(!(sd.flag & SD_HAS_ONLY_VOLUME)) {
			PathState hit_state = state;

#ifdef __EMISSION__
			/* direct light */
			if(kernel_data.integrator.use_direct_light) {
				int all = (kernel_data.integrator.sample_all_lights_direct) ||
				          (state.flag & PATH_RAY_SHADOW_CATCHER);
				kernel_branched_path_surface_connect_light(kg,
					&sd, &emission_sd, &hit_state, throughput, 1.0f, L, all);
			}
#endif  /* __EMISSION__ */

			/* indirect light */
			kernel_branched_path_surface_indirect_light(kg,
				&sd, &indirect_sd, &emission_sd, throughput, 1.0f, &hit_state, L);

			/* continue in case of transparency */
			throughput *= shader_bsdf_transparency(kg, &sd);

			if(is_zero(throughput))
				break;
		}

		/* Update Path State */
		state.flag |= PATH_RAY_TRANSPARENT;
		state.transparent_bounce++;

		ray.P = ray_offset(sd.P, -sd.Ng);
		ray.t -= sd.ray_length; /* clipping works through transparent */


#ifdef __RAY_DIFFERENTIALS__
		ray.dP = sd.dP;
		ray.dD.dx = -sd.dI.dx;
		ray.dD.dy = -sd.dI.dy;
#endif  /* __RAY_DIFFERENTIALS__ */

#ifdef __VOLUME__
		/* enter/exit volume */
		kernel_volume_stack_enter_exit(kg, &sd, state.volume_stack);
#endif  /* __VOLUME__ */
	}
}

ccl_device void kernel_branched_path_trace(KernelGlobals *kg,
	ccl_global float *buffer,
	int sample, int x, int y, int offset, int stride)
{
	/* buffer offset */
	int index = offset + x + y*stride;
	int pass_stride = kernel_data.film.pass_stride;

	buffer += index*pass_stride;

	/* initialize random numbers and ray */
	uint rng_hash;
	Ray ray;

	kernel_path_trace_setup(kg, sample, x, y, &rng_hash, &ray);

	/* integrate */
	PathRadiance L;

	if(ray.t != 0.0f) {
		kernel_branched_path_integrate(kg, rng_hash, sample, ray, buffer, &L);
		kernel_write_result(kg, buffer, sample, &L);
	}
}

#endif  /* __SPLIT_KERNEL__ */

#endif  /* __BRANCHED_PATH__ */

CCL_NAMESPACE_END
