Sample as Lamp option for world shaders, to enable multiple importance sampling.

By default lighting from the world is computed solely with indirect light
sampling. However for more complex environment maps this can be too noisy, as
sampling the BSDF may not easily find the highlights in the environment map
image. By enabling this option, the world background will be sampled as a lamp,
with lighter parts automatically given more samples.

Map Resolution specifies the size of the importance map (res x res). Before
rendering starts, an importance map is generated by "baking" a grayscale image
from the world shader. This will then be used to determine which parts of the
background are light and so should receive more samples than darker parts.
Higher resolutions will result in more accurate sampling but take more setup
time and memory.

Patch by Mike Farnsworth, thanks!

1 files changed, 178 insertions, 0 deletions

diff --git a/intern/cycles/render/light.cpp b/intern/cycles/render/light.cpp
index c8206365373..eea5cfb0137 100644
--- a/intern/cycles/render/light.cpp
+++ b/intern/cycles/render/light.cpp
@@ -26,8 +26,74 @@
 #include "util_foreach.h"
 #include "util_progress.h"
 
+#include "kernel_montecarlo.h"
+
 CCL_NAMESPACE_BEGIN
 
+static void dump_background_pixels(Device *device, DeviceScene *dscene, int res, vector<float3>& pixels)
+{
+	/* create input */
+	int width = res;
+	int height = res;
+
+	device_vector<uint4> d_input;
+	device_vector<float4> d_output;
+
+	uint4 *d_input_data = d_input.resize(width*height);
+
+	for(int y = 0; y < height; y++) {
+		for(int x = 0; x < width; x++) {
+			float u = x/(float)width;
+			float v = y/(float)height;
+			float3 D = -equirectangular_to_direction(u, v);
+
+			uint4 in = make_uint4(__float_as_int(D.x), __float_as_int(D.y), __float_as_int(D.z), 0);
+			d_input_data[x + y*width] = in;
+		}
+	}
+
+	/* compute on device */
+	float4 *d_output_data = d_output.resize(width*height);
+	memset((void*)d_output.data_pointer, 0, d_output.memory_size());
+
+	device->const_copy_to("__data", &dscene->data, sizeof(dscene->data));
+
+	device->mem_alloc(d_input, MEM_READ_ONLY);
+	device->mem_copy_to(d_input);
+	device->mem_alloc(d_output, MEM_WRITE_ONLY);
+
+	DeviceTask main_task(DeviceTask::SHADER);
+	main_task.shader_input = d_input.device_pointer;
+	main_task.shader_output = d_output.device_pointer;
+	main_task.shader_eval_type = SHADER_EVAL_BACKGROUND;
+	main_task.shader_x = 0;
+	main_task.shader_w = width*height;
+
+	list<DeviceTask> split_tasks;
+	main_task.split_max_size(split_tasks, 128*128);
+
+	foreach(DeviceTask& task, split_tasks) {
+		device->task_add(task);
+		device->task_wait();
+	}
+
+	device->mem_copy_from(d_output, 0, 1, d_output.size(), sizeof(float4));
+	device->mem_free(d_input);
+	device->mem_free(d_output);
+
+	d_output_data = reinterpret_cast<float4*>(d_output.data_pointer);
+
+	pixels.resize(width*height);
+
+	for(int y = 0; y < height; y++) {
+		for(int x = 0; x < width; x++) {
+			pixels[y*width + x].x = d_output_data[y*width + x].x;
+			pixels[y*width + x].y = d_output_data[y*width + x].y;
+			pixels[y*width + x].z = d_output_data[y*width + x].z;
+		}
+	}
+}
+
 /* Light */
 
 Light::Light()
@@ -44,6 +110,8 @@ Light::Light()
 	axisv = make_float3(0.0f, 0.0f, 0.0f);
 	sizev = 1.0f;
 
+	map_resolution = 512;
+
 	cast_shadow = true;
 	shader = 0;
 }
@@ -66,6 +134,8 @@ LightManager::~LightManager()
 
 void LightManager::device_update_distribution(Device *device, DeviceScene *dscene, Scene *scene, Progress& progress)
 {
+	progress.set_status("Updating Lights", "Computing distribution");
+
 	/* option to always sample all point lights */
 	bool multi_light = false;
 
@@ -232,6 +302,99 @@ void LightManager::device_update_distribution(Device *device, DeviceScene *dscen
 		dscene->light_distribution.clear();
 }
 
+void LightManager::device_update_background(Device *device, DeviceScene *dscene, Scene *scene, Progress& progress)
+{
+	KernelIntegrator *kintegrator = &dscene->data.integrator;
+	Light *background_light = NULL;
+
+	/* find background light */
+	foreach(Light *light, scene->lights) {
+		if(light->type == LIGHT_BACKGROUND) {
+			background_light = light;
+			break;
+		}
+	}
+
+	/* no background light found, signal renderer to skip sampling */
+	if(!background_light) {
+		kintegrator->pdf_background_res = 0;
+		return;
+	}
+
+	progress.set_status("Updating Lights", "Importance map");
+
+	assert(kintegrator->use_direct_light);
+
+	/* get the resolution from the light's size (we stuff it in there) */
+	int res = background_light->map_resolution;
+	kintegrator->pdf_background_res = res;
+
+	assert(res > 0);
+
+	vector<float3> pixels;
+	dump_background_pixels(device, dscene, res, pixels);
+
+	if(progress.get_cancel())
+		return;
+
+	/* build row distributions and column distribution for the infinite area environment light */
+	int cdf_count = res + 1;
+	float2 *marg_cdf = dscene->light_background_marginal_cdf.resize(cdf_count);
+	float2 *cond_cdf = dscene->light_background_conditional_cdf.resize(cdf_count * cdf_count);
+
+	/* conditional CDFs (rows, U direction) */
+	for(int i = 0; i < res; i++) {
+		float sin_theta = sinf(M_PI_F * (i + 0.5f) / res);
+		float3 env_color = pixels[i * res];
+		float ave_luminamce = average(env_color);
+
+		cond_cdf[i * cdf_count].x = ave_luminamce * sin_theta;
+		cond_cdf[i * cdf_count].y = 0.0f;
+
+		for(int j = 1; j < res; j++) {
+			env_color = pixels[i * res + j];
+			ave_luminamce = average(env_color);
+
+			cond_cdf[i * cdf_count + j].x = ave_luminamce * sin_theta;
+			cond_cdf[i * cdf_count + j].y = cond_cdf[i * cdf_count + j - 1].y + cond_cdf[i * cdf_count + j - 1].x / res;
+		}
+
+		float cdf_total = cond_cdf[i * cdf_count + res - 1].y + cond_cdf[i * cdf_count + res - 1].x / res;
+
+		/* stuff the total into the brightness value for the last entry, because
+		   we are going to normalize the CDFs to 0.0 to 1.0 afterwards */
+		cond_cdf[i * cdf_count + res].x = cdf_total;
+
+		if(cdf_total > 0.0f)
+			for(int j = 1; j < res; j++)
+				cond_cdf[i * cdf_count + j].y /= cdf_total;
+
+		cond_cdf[i * cdf_count + res].y = 1.0f;
+	}
+
+	/* marginal CDFs (column, V direction, sum of rows) */
+	marg_cdf[0].x = cond_cdf[res].x;
+	marg_cdf[0].y = 0.0f;
+
+	for(int i = 1; i < res; i++) {
+		marg_cdf[i].x = cond_cdf[i * cdf_count + res].x;
+		marg_cdf[i].y = marg_cdf[i - 1].y + marg_cdf[i - 1].x / res;
+	}
+
+	float cdf_total = marg_cdf[res - 1].y + marg_cdf[res - 1].x / res;
+	marg_cdf[res].x = cdf_total;
+
+	if(cdf_total > 0.0f)
+		for(int i = 1; i < res; i++)
+			marg_cdf[i].y /= cdf_total;
+
+	marg_cdf[res].y = 1.0f;
+
+	/* update device */
+	device->tex_alloc("__light_background_marginal_cdf", dscene->light_background_marginal_cdf);
+	device->tex_alloc("__light_background_conditional_cdf", dscene->light_background_conditional_cdf);
+}
+
 void LightManager::device_update_points(Device *device, DeviceScene *dscene, Scene *scene)
 {
 	if(scene->lights.size() == 0)
@@ -264,6 +427,14 @@ void LightManager::device_update_points(Device *device, DeviceScene *dscene, Sce
 			light_data[i*LIGHT_SIZE + 2] = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
 			light_data[i*LIGHT_SIZE + 3] = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
 		}
+		else if(light->type == LIGHT_BACKGROUND) {
+			shader_id &= ~SHADER_AREA_LIGHT;
+
+			light_data[i*LIGHT_SIZE + 0] = make_float4(__int_as_float(light->type), 0.0f, 0.0f, 0.0f);
+			light_data[i*LIGHT_SIZE + 1] = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+			light_data[i*LIGHT_SIZE + 2] = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+			light_data[i*LIGHT_SIZE + 3] = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+		}
 		else if(light->type == LIGHT_AREA) {
 			float3 axisu = light->axisu*(light->sizeu*light->size);
 			float3 axisv = light->axisv*(light->sizev*light->size);
@@ -291,6 +462,9 @@ void LightManager::device_update(Device *device, DeviceScene *dscene, Scene *sce
 	device_update_distribution(device, dscene, scene, progress);
 	if(progress.get_cancel()) return;
 
+	device_update_background(device, dscene, scene, progress);
+	if(progress.get_cancel()) return;
+
 	need_update = false;
 }
 
@@ -298,9 +472,13 @@ void LightManager::device_free(Device *device, DeviceScene *dscene)
 {
 	device->tex_free(dscene->light_distribution);
 	device->tex_free(dscene->light_data);
+	device->tex_free(dscene->light_background_marginal_cdf);
+	device->tex_free(dscene->light_background_conditional_cdf);
 
 	dscene->light_distribution.clear();
 	dscene->light_data.clear();
+	dscene->light_background_marginal_cdf.clear();
+	dscene->light_background_conditional_cdf.clear();
 }
 
 void LightManager::tag_update(Scene *scene)