/*
 * Copyright 2011-2015 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

/* This kernel takes care of the logic to process "material of type holdout",
 * indirect primitive emission, bsdf blurring, probabilistic path termination
 * and AO.
 *
 * This kernels determines the rays for which a shadow_blocked() function
 * associated with AO should be executed. Those rays for which a
 * shadow_blocked() function for AO must be executed are marked with flag
 * RAY_SHADOW_RAY_CAST_ao and enqueued into the queue
 * QUEUE_SHADOW_RAY_CAST_AO_RAYS
 *
 * Ray state of rays that are terminated in this kernel are changed to RAY_UPDATE_BUFFER
 *
 * Note on Queues:
 * This kernel fetches rays from the queue QUEUE_ACTIVE_AND_REGENERATED_RAYS
 * and processes only the rays of state RAY_ACTIVE.
 * There are different points in this kernel where a ray may terminate and
 * reach RAY_UPDATE_BUFFER state. These rays are enqueued into
 * QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS queue. These rays will still be present
 * in QUEUE_ACTIVE_AND_REGENERATED_RAYS queue, but since their ray-state has
 * been changed to RAY_UPDATE_BUFFER, there is no problem.
 *
 * State of queues when this kernel is called:
 * At entry,
 *   - QUEUE_ACTIVE_AND_REGENERATED_RAYS will be filled with RAY_ACTIVE and
 *     RAY_REGENERATED rays
 *   - QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS will be filled with
 *     RAY_TO_REGENERATE rays.
 *   - QUEUE_SHADOW_RAY_CAST_AO_RAYS will be empty.
 * At exit,
 *   - QUEUE_ACTIVE_AND_REGENERATED_RAYS will be filled with RAY_ACTIVE,
 *     RAY_REGENERATED and RAY_UPDATE_BUFFER rays.
 *   - QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS will be filled with
 *     RAY_TO_REGENERATE and RAY_UPDATE_BUFFER rays.
 *   - QUEUE_SHADOW_RAY_CAST_AO_RAYS will be filled with rays marked with
 *     flag RAY_SHADOW_RAY_CAST_AO
 */

ccl_device void kernel_holdout_emission_blurring_pathtermination_ao(
        KernelGlobals *kg,
        ccl_local_param BackgroundAOLocals *locals)
{
	if(ccl_local_id(0) == 0 && ccl_local_id(1) == 0) {
		locals->queue_atomics_bg = 0;
		locals->queue_atomics_ao = 0;
	}
	ccl_barrier(CCL_LOCAL_MEM_FENCE);

#ifdef __AO__
	char enqueue_flag = 0;
#endif
	int ray_index = ccl_global_id(1) * ccl_global_size(0) + ccl_global_id(0);
	ray_index = get_ray_index(kg, ray_index,
	                          QUEUE_ACTIVE_AND_REGENERATED_RAYS,
	                          kernel_split_state.queue_data,
	                          kernel_split_params.queue_size,
	                          0);

#ifdef __COMPUTE_DEVICE_GPU__
	/* If we are executing on a GPU device, we exit all threads that are not
	 * required.
	 *
	 * If we are executing on a CPU device, then we need to keep all threads
	 * active since we have barrier() calls later in the kernel. CPU devices,
	 * expect all threads to execute barrier statement.
	 */
	if(ray_index == QUEUE_EMPTY_SLOT) {
		return;
	}
#endif  /* __COMPUTE_DEVICE_GPU__ */

#ifndef __COMPUTE_DEVICE_GPU__
	if(ray_index != QUEUE_EMPTY_SLOT) {
#endif

	ccl_global PathState *state = 0x0;
	float3 throughput;

	ccl_global char *ray_state = kernel_split_state.ray_state;
	ShaderData *sd = &kernel_split_state.sd[ray_index];

	if(IS_STATE(ray_state, ray_index, RAY_ACTIVE)) {
		uint buffer_offset = kernel_split_state.buffer_offset[ray_index];
		ccl_global float *buffer = kernel_split_params.tile.buffer + buffer_offset;

		ccl_global Ray *ray = &kernel_split_state.ray[ray_index];
		ShaderData *emission_sd = &kernel_split_state.sd_DL_shadow[ray_index];
		PathRadiance *L = &kernel_split_state.path_radiance[ray_index];

		throughput = kernel_split_state.throughput[ray_index];
		state = &kernel_split_state.path_state[ray_index];

		if(!kernel_path_shader_apply(kg,
		                             sd,
		                             state,
		                             ray,
		                             throughput,
		                             emission_sd,
		                             L,
		                             buffer))
		{
			kernel_split_path_end(kg, ray_index);
		}
	}

	if(IS_STATE(ray_state, ray_index, RAY_ACTIVE)) {
		/* 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) {
			kernel_split_path_end(kg, ray_index);
		}
		else if(probability < 1.0f) {
			float terminate = path_state_rng_1D(kg, state, PRNG_TERMINATE);
			if(terminate >= probability) {
				kernel_split_path_end(kg, ray_index);
			}
			else {
				kernel_split_state.throughput[ray_index] = throughput/probability;
			}
		}

		if(IS_STATE(ray_state, ray_index, RAY_ACTIVE)) {
			PathRadiance *L = &kernel_split_state.path_radiance[ray_index];
			kernel_update_denoising_features(kg, sd, state, L);
		}
	}

#ifdef __AO__
	if(IS_STATE(ray_state, ray_index, RAY_ACTIVE)) {
		/* ambient occlusion */
		if(kernel_data.integrator.use_ambient_occlusion || (sd->flag & SD_AO)) {
			enqueue_flag = 1;
		}
	}
#endif  /* __AO__ */

#ifndef __COMPUTE_DEVICE_GPU__
	}
#endif

#ifdef __AO__
	/* Enqueue to-shadow-ray-cast rays. */
	enqueue_ray_index_local(ray_index,
	                        QUEUE_SHADOW_RAY_CAST_AO_RAYS,
	                        enqueue_flag,
	                        kernel_split_params.queue_size,
	                        &locals->queue_atomics_ao,
	                        kernel_split_state.queue_data,
	                        kernel_split_params.queue_index);
#endif
}

CCL_NAMESPACE_END
