/*
 * 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.
 */

#include "kernel_split_common.h"

/* Note on kernel_background_buffer_update kernel.
 * This is the fourth kernel in the ray tracing logic, and the third
 * of the path iteration kernels. This kernel takes care of rays that hit
 * the background (sceneintersect kernel), and for the rays of
 * state RAY_UPDATE_BUFFER it updates the ray's accumulated radiance in
 * the output buffer. This kernel also takes care of rays that have been determined
 * to-be-regenerated.
 *
 * We will empty QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS queue in this kernel
 *
 * Typically all rays that are in state RAY_HIT_BACKGROUND, RAY_UPDATE_BUFFER
 * will be eventually set to RAY_TO_REGENERATE state in this kernel. Finally all rays of ray_state
 * RAY_TO_REGENERATE will be regenerated and put in queue QUEUE_ACTIVE_AND_REGENERATED_RAYS.
 *
 * The input and output are as follows,
 *
 * rng_coop ---------------------------------------------|--- kernel_background_buffer_update --|--- PathRadiance_coop
 * throughput_coop --------------------------------------|                                      |--- L_transparent_coop
 * per_sample_output_buffers ----------------------------|                                      |--- per_sample_output_buffers
 * Ray_coop ---------------------------------------------|                                      |--- ray_state
 * PathState_coop ---------------------------------------|                                      |--- Queue_data (QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS)
 * L_transparent_coop -----------------------------------|                                      |--- Queue_data (QUEUE_ACTIVE_AND_REGENERATED_RAYS)
 * ray_state --------------------------------------------|                                      |--- Queue_index (QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS)
 * Queue_data (QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS) ----|                                      |--- Queue_index (QUEUE_ACTIVE_AND_REGENERATED_RAYS)
 * Queue_index (QUEUE_ACTIVE_AND_REGENERATED_RAYS) ------|                                      |--- work_array
 * parallel_samples -------------------------------------|                                      |--- PathState_coop
 * end_sample -------------------------------------------|                                      |--- throughput_coop
 * kg (globals) -----------------------------------------|                                      |--- rng_coop
 * rng_state --------------------------------------------|                                      |--- Ray
 * PathRadiance_coop ------------------------------------|                                      |
 * sw ---------------------------------------------------|                                      |
 * sh ---------------------------------------------------|                                      |
 * sx ---------------------------------------------------|                                      |
 * sy ---------------------------------------------------|                                      |
 * stride -----------------------------------------------|                                      |
 * work_array -------------------------------------------|                                      |--- work_array
 * queuesize --------------------------------------------|                                      |
 * start_sample -----------------------------------------|                                      |--- work_pool_wgs
 * work_pool_wgs ----------------------------------------|                                      |
 * num_samples ------------------------------------------|                                      |
 *
 * note on sd : sd argument is neither an input nor an output for this kernel. It is just filled and consumed here itself.
 * Note on Queues :
 * This kernel fetches rays from QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS queue.
 *
 * State of queues when this kernel is called :
 * At entry,
 * QUEUE_ACTIVE_AND_REGENERATED_RAYS will be filled with RAY_ACTIVE rays
 * QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS will be filled with RAY_UPDATE_BUFFER, RAY_HIT_BACKGROUND, RAY_TO_REGENERATE rays
 * At exit,
 * QUEUE_ACTIVE_AND_REGENERATED_RAYS will be filled with RAY_ACTIVE and RAY_REGENERATED rays
 * QUEUE_HITBG_BUFF_UPDATE_TOREGEN_RAYS will be empty
 */
ccl_device char kernel_background_buffer_update(
        KernelGlobals *kg,
        ccl_global float *per_sample_output_buffers,
        ccl_global uint *rng_state,
        ccl_global uint *rng_coop,             /* Required for buffer Update */
        ccl_global float3 *throughput_coop,    /* Required for background hit processing */
        PathRadiance *PathRadiance_coop,       /* Required for background hit processing and buffer Update */
        ccl_global Ray *Ray_coop,              /* Required for background hit processing */
        ccl_global PathState *PathState_coop,  /* Required for background hit processing */
        ccl_global float *L_transparent_coop,  /* Required for background hit processing and buffer Update */
        ccl_global char *ray_state,            /* Stores information on the current state of a ray */
        int sw, int sh, int sx, int sy, int stride,
        int rng_state_offset_x,
        int rng_state_offset_y,
        int rng_state_stride,
        ccl_global unsigned int *work_array,   /* Denotes work of each ray */
        int end_sample,
        int start_sample,
#ifdef __WORK_STEALING__
        ccl_global unsigned int *work_pool_wgs,
        unsigned int num_samples,
#endif
#ifdef __KERNEL_DEBUG__
        DebugData *debugdata_coop,
#endif
        int parallel_samples,                  /* Number of samples to be processed in parallel */
        int ray_index)
{
	char enqueue_flag = 0;
#ifdef __KERNEL_DEBUG__
	DebugData *debug_data = &debugdata_coop[ray_index];
#endif
	ccl_global PathState *state = &PathState_coop[ray_index];
	PathRadiance *L = L = &PathRadiance_coop[ray_index];
	ccl_global Ray *ray = &Ray_coop[ray_index];
	ccl_global float3 *throughput = &throughput_coop[ray_index];
	ccl_global float *L_transparent = &L_transparent_coop[ray_index];
	ccl_global uint *rng = &rng_coop[ray_index];

#ifdef __WORK_STEALING__
	unsigned int my_work;
	ccl_global float *initial_per_sample_output_buffers;
	ccl_global uint *initial_rng;
#endif
	unsigned int sample;
	unsigned int tile_x;
	unsigned int tile_y;
	unsigned int pixel_x;
	unsigned int pixel_y;
	unsigned int my_sample_tile;

#ifdef __WORK_STEALING__
	my_work = work_array[ray_index];
	sample = get_my_sample(my_work, sw, sh, parallel_samples, ray_index) + start_sample;
	get_pixel_tile_position(&pixel_x, &pixel_y,
	                        &tile_x, &tile_y,
	                        my_work,
	                        sw, sh, sx, sy,
	                        parallel_samples,
	                        ray_index);
	my_sample_tile = 0;
	initial_per_sample_output_buffers = per_sample_output_buffers;
	initial_rng = rng_state;
#else  /* __WORK_STEALING__ */
	sample = work_array[ray_index];
	int tile_index = ray_index / parallel_samples;
	/* buffer and rng_state's stride is "stride". Find x and y using ray_index */
	tile_x = tile_index % sw;
	tile_y = tile_index / sw;
	my_sample_tile = ray_index - (tile_index * parallel_samples);
#endif  /* __WORK_STEALING__ */

	rng_state += (rng_state_offset_x + tile_x) + (rng_state_offset_y + tile_y) * rng_state_stride;
	per_sample_output_buffers += (((tile_x + (tile_y * stride)) * parallel_samples) + my_sample_tile) * kernel_data.film.pass_stride;

	if(IS_STATE(ray_state, ray_index, RAY_HIT_BACKGROUND)) {
		/* eval background shader if nothing hit */
		if(kernel_data.background.transparent && (state->flag & PATH_RAY_CAMERA)) {
			*L_transparent = (*L_transparent) + average((*throughput));
#ifdef __PASSES__
			if(!(kernel_data.film.pass_flag & PASS_BACKGROUND))
#endif
				ASSIGN_RAY_STATE(ray_state, ray_index, RAY_UPDATE_BUFFER);
		}

		if(IS_STATE(ray_state, ray_index, RAY_HIT_BACKGROUND)) {
#ifdef __BACKGROUND__
			/* sample background shader */
			float3 L_background = indirect_background(kg, state, ray);
			path_radiance_accum_background(L, (*throughput), L_background, state->bounce);
#endif
			ASSIGN_RAY_STATE(ray_state, ray_index, RAY_UPDATE_BUFFER);
		}
	}

	if(IS_STATE(ray_state, ray_index, RAY_UPDATE_BUFFER)) {
		float3 L_sum = path_radiance_clamp_and_sum(kg, L);
		kernel_write_light_passes(kg, per_sample_output_buffers, L, sample);
#ifdef __KERNEL_DEBUG__
		kernel_write_debug_passes(kg, per_sample_output_buffers, state, debug_data, sample);
#endif
		float4 L_rad = make_float4(L_sum.x, L_sum.y, L_sum.z, 1.0f - (*L_transparent));

		/* accumulate result in output buffer */
		kernel_write_pass_float4(per_sample_output_buffers, sample, L_rad);
		path_rng_end(kg, rng_state, *rng);

		ASSIGN_RAY_STATE(ray_state, ray_index, RAY_TO_REGENERATE);
	}

	if(IS_STATE(ray_state, ray_index, RAY_TO_REGENERATE)) {
#ifdef __WORK_STEALING__
		/* We have completed current work; So get next work */
		int valid_work = get_next_work(work_pool_wgs, &my_work, sw, sh, num_samples, parallel_samples, ray_index);
		if(!valid_work) {
			/* If work is invalid, this means no more work is available and the thread may exit */
			ASSIGN_RAY_STATE(ray_state, ray_index, RAY_INACTIVE);
		}
#else  /* __WORK_STEALING__ */
		if((sample + parallel_samples) >= end_sample) {
			ASSIGN_RAY_STATE(ray_state, ray_index, RAY_INACTIVE);
		}
#endif  /* __WORK_STEALING__ */

		if(IS_STATE(ray_state, ray_index, RAY_TO_REGENERATE)) {
#ifdef __WORK_STEALING__
			work_array[ray_index] = my_work;
			/* Get the sample associated with the current work */
			sample = get_my_sample(my_work, sw, sh, parallel_samples, ray_index) + start_sample;
			/* Get pixel and tile position associated with current work */
			get_pixel_tile_position(&pixel_x, &pixel_y, &tile_x, &tile_y, my_work, sw, sh, sx, sy, parallel_samples, ray_index);
			my_sample_tile = 0;

			/* Remap rng_state according to the current work */
			rng_state = initial_rng + ((rng_state_offset_x + tile_x) + (rng_state_offset_y + tile_y) * rng_state_stride);
			/* Remap per_sample_output_buffers according to the current work */
			per_sample_output_buffers = initial_per_sample_output_buffers
				+ (((tile_x + (tile_y * stride)) * parallel_samples) + my_sample_tile) * kernel_data.film.pass_stride;
#else  /* __WORK_STEALING__ */
			work_array[ray_index] = sample + parallel_samples;
			sample = work_array[ray_index];

			/* Get ray position from ray index */
			pixel_x = sx + ((ray_index / parallel_samples) % sw);
			pixel_y = sy + ((ray_index / parallel_samples) / sw);
#endif  /* __WORK_STEALING__ */

			/* Initialize random numbers and ray. */
			kernel_path_trace_setup(kg, rng_state, sample, pixel_x, pixel_y, rng, ray);

			if(ray->t != 0.0f) {
				/* Initialize throughput, L_transparent, Ray, PathState;
				 * These rays proceed with path-iteration.
				 */
				*throughput = make_float3(1.0f, 1.0f, 1.0f);
				*L_transparent = 0.0f;
				path_radiance_init(L, kernel_data.film.use_light_pass);
				path_state_init(kg, state, rng, sample, ray);
#ifdef __KERNEL_DEBUG__
				debug_data_init(debug_data);
#endif
				ASSIGN_RAY_STATE(ray_state, ray_index, RAY_REGENERATED);
				enqueue_flag = 1;
			} else {
				/* These rays do not participate in path-iteration. */
				float4 L_rad = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
				/* Accumulate result in output buffer. */
				kernel_write_pass_float4(per_sample_output_buffers, sample, L_rad);
				path_rng_end(kg, rng_state, *rng);

				ASSIGN_RAY_STATE(ray_state, ray_index, RAY_TO_REGENERATE);
			}
		}
	}
	return enqueue_flag;
}
