/*
 * Copyright 2011, Blender Foundation.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

CCL_NAMESPACE_BEGIN

typedef struct LightSample {
	float3 P;
	float3 D;
	float3 Ng;
	float t;
	int object;
	int prim;
	int shader;
	LightType type;
} LightSample;

/* Regular Light */

__device float3 disk_light_sample(float3 v, float randu, float randv)
{
	float3 ru, rv;

	make_orthonormals(v, &ru, &rv);
	to_unit_disk(&randu, &randv);

	return ru*randu + rv*randv;
}

__device float3 distant_light_sample(float3 D, float size, float randu, float randv)
{
	return normalize(D + disk_light_sample(D, randu, randv)*size);
}

__device float3 sphere_light_sample(float3 P, float3 center, float size, float randu, float randv)
{
	return disk_light_sample(normalize(P - center), randu, randv)*size;
}

__device float3 area_light_sample(float3 axisu, float3 axisv, float randu, float randv)
{
	randu = randu - 0.5f;
	randv = randv - 0.5f;

	return axisu*randu + axisv*randv;
}

__device float3 background_light_sample(KernelGlobals *kg, float randu, float randv, float *pdf)
{
	/* for the following, the CDF values are actually a pair of floats, with the
	   function value as X and the actual CDF as Y.  The last entry's function
	   value is the CDF total. */
	int res = kernel_data.integrator.pdf_background_res;
	int cdf_count = res + 1;

	/* this is basically std::lower_bound as used by pbrt */
	int first = 0;
	int count = res;

	while(count > 0) {
		int step = count >> 1;
		int middle = first + step;

		if(kernel_tex_fetch(__light_background_marginal_cdf, middle).y < randv) {
			first = middle + 1;
			count -= step + 1;
		}
		else
			count = step;
	}

	int index_v = max(0, first - 1);
	kernel_assert(index_v >= 0 && index_v < res);

	float2 cdf_v = kernel_tex_fetch(__light_background_marginal_cdf, index_v);
	float2 cdf_next_v = kernel_tex_fetch(__light_background_marginal_cdf, index_v + 1);
	float2 cdf_last_v = kernel_tex_fetch(__light_background_marginal_cdf, res);

	/* importance-sampled V direction */
	float dv = (randv - cdf_v.y) / (cdf_next_v.y - cdf_v.y);
	float v = (index_v + dv) / res;

	/* this is basically std::lower_bound as used by pbrt */
	first = 0;
	count = res;
	while(count > 0) {
		int step = count >> 1;
		int middle = first + step;

		if(kernel_tex_fetch(__light_background_conditional_cdf, index_v * cdf_count + middle).y < randu) {
			first = middle + 1;
			count -= step + 1;
		}
		else
			count = step;
	}

	int index_u = max(0, first - 1);
	kernel_assert(index_u >= 0 && index_u < res);

	float2 cdf_u = kernel_tex_fetch(__light_background_conditional_cdf, index_v * cdf_count + index_u);
	float2 cdf_next_u = kernel_tex_fetch(__light_background_conditional_cdf, index_v * cdf_count + index_u + 1);
	float2 cdf_last_u = kernel_tex_fetch(__light_background_conditional_cdf, index_v * cdf_count + res);

	/* importance-sampled U direction */
	float du = (randu - cdf_u.y) / (cdf_next_u.y - cdf_u.y);
	float u = (index_u + du) / res;

	/* spherical coordinates */
	float theta = v * M_PI_F;
	float phi = u * M_PI_F * 2.0f;

	/* compute pdf */
	float denom = cdf_last_u.x * cdf_last_v.x;
	float sin_theta = sinf(theta);

	if(sin_theta == 0.0f || denom == 0.0f)
		*pdf = 0.0f;
	else
		*pdf = (cdf_u.x * cdf_v.x)/(2.0f * M_PI_F * M_PI_F * sin_theta * denom);

	*pdf *= kernel_data.integrator.pdf_lights;

	/* compute direction */
	return spherical_to_direction(theta, phi);
}

__device float background_light_pdf(KernelGlobals *kg, float3 direction)
{
	float2 uv = direction_to_equirectangular(direction);
	int res = kernel_data.integrator.pdf_background_res;

	float sin_theta = sinf(uv.y * M_PI_F);

	if(sin_theta == 0.0f)
		return 0.0f;

	int index_u = clamp((int)(uv.x * res), 0, res - 1);
	int index_v = clamp((int)(uv.y * res), 0, res - 1);

	/* pdfs in V direction */
	float2 cdf_last_u = kernel_tex_fetch(__light_background_conditional_cdf, index_v * (res + 1) + res);
	float2 cdf_last_v = kernel_tex_fetch(__light_background_marginal_cdf, res);

	float denom = cdf_last_u.x * cdf_last_v.x;

	if(denom == 0.0f)
		return 0.0f;

	/* pdfs in U direction */
	float2 cdf_u = kernel_tex_fetch(__light_background_conditional_cdf, index_v * (res + 1) + index_u);
	float2 cdf_v = kernel_tex_fetch(__light_background_marginal_cdf, index_v);

	float pdf = (cdf_u.x * cdf_v.x)/(2.0f * M_PI_F * M_PI_F * sin_theta * denom);

	return pdf * kernel_data.integrator.pdf_lights;
}

__device void regular_light_sample(KernelGlobals *kg, int point,
	float randu, float randv, float3 P, LightSample *ls, float *pdf)
{
	float4 data0 = kernel_tex_fetch(__light_data, point*LIGHT_SIZE + 0);
	float4 data1 = kernel_tex_fetch(__light_data, point*LIGHT_SIZE + 1);

	LightType type = (LightType)__float_as_int(data0.x);
	ls->type = type;

	if(type == LIGHT_DISTANT) {
		/* distant light */
		float3 D = make_float3(data0.y, data0.z, data0.w);
		float size = data1.y;

		if(size > 0.0f)
			D = distant_light_sample(D, size, randu, randv);

		ls->P = D;
		ls->Ng = D;
		ls->D = -D;
		ls->t = FLT_MAX;
	}
#ifdef __BACKGROUND_MIS__
	else if(type == LIGHT_BACKGROUND) {
		/* infinite area light (e.g. light dome or env light) */
		float3 D = background_light_sample(kg, randu, randv, pdf);

		ls->P = D;
		ls->Ng = D;
		ls->D = -D;
		ls->t = FLT_MAX;
	}
#endif
	else {
		ls->P = make_float3(data0.y, data0.z, data0.w);

		if(type == LIGHT_POINT) {
			float size = data1.y;

			/* sphere light */
			if(size > 0.0f)
				ls->P += sphere_light_sample(P, ls->P, size, randu, randv);

			ls->Ng = normalize(P - ls->P);
		}
		else {
			/* area light */
			float4 data2 = kernel_tex_fetch(__light_data, point*LIGHT_SIZE + 2);
			float4 data3 = kernel_tex_fetch(__light_data, point*LIGHT_SIZE + 3);

			float3 axisu = make_float3(data1.y, data1.z, data2.w);
			float3 axisv = make_float3(data2.y, data2.z, data2.w);
			float3 D = make_float3(data3.y, data3.z, data3.w);

			ls->P += area_light_sample(axisu, axisv, randu, randv);
			ls->Ng = D;
		}

		ls->t = 0.0f;
	}

	ls->shader = __float_as_int(data1.x);
	ls->object = ~0;
	ls->prim = ~0;
}

__device float regular_light_pdf(KernelGlobals *kg,
	const float3 Ng, const float3 I, float t)
{
	float pdf = kernel_data.integrator.pdf_lights;

	if(t == FLT_MAX)
		return pdf;

	float cos_pi = dot(Ng, I);

	if(cos_pi <= 0.0f)
		return 0.0f;

	return t*t*pdf/cos_pi;
}

/* Triangle Light */

__device void triangle_light_sample(KernelGlobals *kg, int prim, int object,
	float randu, float randv, LightSample *ls)
{
	/* triangle, so get position, normal, shader */
	ls->P = triangle_sample_MT(kg, prim, randu, randv);
	ls->Ng = triangle_normal_MT(kg, prim, &ls->shader);
	ls->object = object;
	ls->prim = prim;
	ls->t = 0.0f;
	ls->type = LIGHT_AREA;

#ifdef __INSTANCING__
	/* instance transform */
	if(ls->object >= 0) {
		object_position_transform(kg, ls->object, &ls->P);
		object_normal_transform(kg, ls->object, &ls->Ng);
	}
#endif
}

__device float triangle_light_pdf(KernelGlobals *kg,
	const float3 Ng, const float3 I, float t)
{
	float cos_pi = fabsf(dot(Ng, I));

	if(cos_pi == 0.0f)
		return 0.0f;
	
	return (t*t*kernel_data.integrator.pdf_triangles)/cos_pi;
}

/* Light Distribution */

__device int light_distribution_sample(KernelGlobals *kg, float randt)
{
	/* this is basically std::upper_bound as used by pbrt, to find a point light or
	   triangle to emit from, proportional to area. a good improvement would be to
	   also sample proportional to power, though it's not so well defined with
	   OSL shaders. */
	int first = 0;
	int len = kernel_data.integrator.num_distribution + 1;

	while(len > 0) {
		int half_len = len >> 1;
		int middle = first + half_len;

		if(randt < kernel_tex_fetch(__light_distribution, middle).x) {
			len = half_len;
		}
		else {
			first = middle + 1;
			len = len - half_len - 1;
		}
	}

	first = max(0, first-1);
	kernel_assert(first >= 0 && first < kernel_data.integrator.num_distribution);

	return first;
}

/* Generic Light */

__device void light_sample(KernelGlobals *kg, float randt, float randu, float randv, float3 P, LightSample *ls, float *pdf)
{
	/* sample index */
	int index = light_distribution_sample(kg, randt);

	/* fetch light data */
	float4 l = kernel_tex_fetch(__light_distribution, index);
	int prim = __float_as_int(l.y);

	if(prim >= 0) {
		int object = __float_as_int(l.w);
		triangle_light_sample(kg, prim, object, randu, randv, ls);
	}
	else {
		int point = -prim-1;
		regular_light_sample(kg, point, randu, randv, P, ls, pdf);
	}

	/* compute incoming direction and distance */
	if(ls->t != FLT_MAX)
		ls->D = normalize_len(ls->P - P, &ls->t);
}

__device float light_sample_pdf(KernelGlobals *kg, LightSample *ls, float3 I, float t)
{
	float pdf;

	if(ls->prim != ~0)
		pdf = triangle_light_pdf(kg, ls->Ng, I, t);
	else
		pdf = regular_light_pdf(kg, ls->Ng, I, t);
	
	return pdf;
}

__device void light_select(KernelGlobals *kg, int index, float randu, float randv, float3 P, LightSample *ls, float *pdf)
{
	regular_light_sample(kg, index, randu, randv, P, ls, pdf);
}

__device float light_select_pdf(KernelGlobals *kg, LightSample *ls, float3 I, float t)
{
	return regular_light_pdf(kg, ls->Ng, I, t);
}

CCL_NAMESPACE_END

