Cycles: multiple importance sampling for lamps, which helps reduce noise for

big lamps and sharp glossy reflections. This was already supported for mesh
lights and the background, so lamps should do it too.

This is not for free and it's a bit slower than I hoped even though there is
no extra BVH ray intersection. I'll try to optimize it more later.

* Area lights look a bit different now, they had the wrong shape before.
* Also fixes a sampling issue in the non-progressive integrator.
* Only enabled for the CPU, will test on the GPU later.
* An option to disable this will be added for situations where it does not help.

Same time comparison before/after:
http://www.pasteall.org/pic/show.php?id=43313
http://www.pasteall.org/pic/show.php?id=43314

1 files changed, 22 insertions, 5 deletions

diff --git a/intern/cycles/render/light.cpp b/intern/cycles/render/light.cpp
index c8e3e94ec98..1b94d603a26 100644
--- a/intern/cycles/render/light.cpp
+++ b/intern/cycles/render/light.cpp
@@ -323,6 +323,7 @@ void LightManager::device_update_distribution(Device *device, DeviceScene *dscen
 		/* precompute pdfs */
 		kintegrator->pdf_triangles = 0.0f;
 		kintegrator->pdf_lights = 0.0f;
+		kintegrator->inv_pdf_lights = 0.0f;
 
 		/* sample one, with 0.5 probability of light or triangle */
 		kintegrator->num_all_lights = num_lights;
@@ -337,6 +338,8 @@ void LightManager::device_update_distribution(Device *device, DeviceScene *dscen
 			kintegrator->pdf_lights = 1.0f/num_lights;
 			if(trianglearea > 0.0f)
 				kintegrator->pdf_lights *= 0.5f;
+
+			kintegrator->inv_pdf_lights = 1.0f/kintegrator->pdf_lights;
 		}
 
 		/* CDF */
@@ -349,6 +352,7 @@ void LightManager::device_update_distribution(Device *device, DeviceScene *dscen
 		kintegrator->num_all_lights = 0;
 		kintegrator->pdf_triangles = 0.0f;
 		kintegrator->pdf_lights = 0.0f;
+		kintegrator->inv_pdf_lights = 0.0f;
 	}
 }
 
@@ -475,16 +479,25 @@ void LightManager::device_update_points(Device *device, DeviceScene *dscene, Sce
 		if(light->type == LIGHT_POINT) {
 			shader_id &= ~SHADER_AREA_LIGHT;
 
+			float radius = light->size;
+			float invarea = (radius > 0.0f)? 1.0f/(M_PI_F*radius*radius): 1.0f;
+
 			light_data[i*LIGHT_SIZE + 0] = make_float4(__int_as_float(light->type), co.x, co.y, co.z);
-			light_data[i*LIGHT_SIZE + 1] = make_float4(__int_as_float(shader_id), light->size, 0.0f, 0.0f);
+			light_data[i*LIGHT_SIZE + 1] = make_float4(__int_as_float(shader_id), radius, invarea, 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(samples, 0.0f, 0.0f, 0.0f);
 		}
 		else if(light->type == LIGHT_DISTANT) {
 			shader_id &= ~SHADER_AREA_LIGHT;
 
+			float radius = light->size;
+			float angle = atanf(radius);
+			float cosangle = cosf(angle);
+			float area = M_PI_F*radius*radius;
+			float invarea = (area > 0.0f)? 1.0f/area: 1.0f;
+
 			light_data[i*LIGHT_SIZE + 0] = make_float4(__int_as_float(light->type), dir.x, dir.y, dir.z);
-			light_data[i*LIGHT_SIZE + 1] = make_float4(__int_as_float(shader_id), light->size, 0.0f, 0.0f);
+			light_data[i*LIGHT_SIZE + 1] = make_float4(__int_as_float(shader_id), radius, cosangle, invarea);
 			light_data[i*LIGHT_SIZE + 2] = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
 			light_data[i*LIGHT_SIZE + 3] = make_float4(samples, 0.0f, 0.0f, 0.0f);
 		}
@@ -499,21 +512,25 @@ void LightManager::device_update_points(Device *device, DeviceScene *dscene, Sce
 		else if(light->type == LIGHT_AREA) {
 			float3 axisu = light->axisu*(light->sizeu*light->size);
 			float3 axisv = light->axisv*(light->sizev*light->size);
+			float area = len(axisu)*len(axisv);
+			float invarea = (area > 0.0f)? 1.0f/area: 0.0f;
 
 			light_data[i*LIGHT_SIZE + 0] = make_float4(__int_as_float(light->type), co.x, co.y, co.z);
 			light_data[i*LIGHT_SIZE + 1] = make_float4(__int_as_float(shader_id), axisu.x, axisu.y, axisu.z);
-			light_data[i*LIGHT_SIZE + 2] = make_float4(0.0f, axisv.x, axisv.y, axisv.z);
+			light_data[i*LIGHT_SIZE + 2] = make_float4(invarea, axisv.x, axisv.y, axisv.z);
 			light_data[i*LIGHT_SIZE + 3] = make_float4(samples, dir.x, dir.y, dir.z);
 		}
 		else if(light->type == LIGHT_SPOT) {
 			shader_id &= ~SHADER_AREA_LIGHT;
 
+			float radius = light->size;
+			float invarea = (radius > 0.0f)? 1.0f/(M_PI_F*radius*radius): 1.0f;
 			float spot_angle = cosf(light->spot_angle*0.5f);
 			float spot_smooth = (1.0f - spot_angle)*light->spot_smooth;
 
 			light_data[i*LIGHT_SIZE + 0] = make_float4(__int_as_float(light->type), co.x, co.y, co.z);
-			light_data[i*LIGHT_SIZE + 1] = make_float4(__int_as_float(shader_id), light->size, dir.x, dir.y);
-			light_data[i*LIGHT_SIZE + 2] = make_float4(dir.z, spot_angle, spot_smooth, 0.0f);
+			light_data[i*LIGHT_SIZE + 1] = make_float4(__int_as_float(shader_id), radius, invarea, spot_angle);
+			light_data[i*LIGHT_SIZE + 2] = make_float4(spot_smooth, dir.x, dir.y, dir.z);
 			light_data[i*LIGHT_SIZE + 3] = make_float4(samples, 0.0f, 0.0f, 0.0f);
 		}
 	}