Eevee: Add irradiance smoothing

This is a parameter that will make the interpolation between irradiance
cells of a same Irradiance Volume smoother, reducing the weight of the
light leaking correction factors.

It is usefull in some cases to avoid harsh lighting transition that can
happen when a sample point it near a surface.

release/scripts/startup/bl_ui/properties_render.py

@@ -446,6 +446,8 @@ class RENDER_PT_eevee_indirect_lighting(RenderButtonsPanel, Panel):
         col.prop(props, "gi_diffuse_bounces")
         col.prop(props, "gi_cubemap_resolution")
         col.prop(props, "gi_visibility_resolution", text="Diffuse Occlusion")
+        col.prop(props, "gi_irradiance_smoothing")
+
 
 class RENDER_PT_eevee_indirect_lighting_display(RenderButtonsPanel, Panel):
     bl_label = "Display"

source/blender/blenkernel/intern/scene.c

@@ -872,6 +872,7 @@ void BKE_scene_init(Scene *sce)
 	sce->eevee.gi_visibility_resolution = 32;
 	sce->eevee.gi_cubemap_draw_size = 0.3f;
 	sce->eevee.gi_irradiance_draw_size = 0.1f;
+	sce->eevee.gi_irradiance_smoothing = 0.1f;
 
 	sce->eevee.taa_samples = 16;
 	sce->eevee.taa_render_samples = 64;

source/blender/blenloader/intern/versioning_280.c

@@ -2271,6 +2271,12 @@ void blo_do_versions_280(FileData *fd, Library *UNUSED(lib), Main *bmain)
 			}
 		}
 
+		if (!DNA_struct_elem_find(fd->filesdna, "SceneEEVEE", "float", "gi_irradiance_smoothing")) {
+			for (Scene *scene = bmain->scene.first; scene; scene = scene->id.next) {
+				scene->eevee.gi_irradiance_smoothing = 0.1f;
+			}
+		}
+
 		if (!DNA_struct_elem_find(fd->filesdna, "Lamp", "float", "att_dist")) {
 			for (Lamp *la = bmain->lamp.first; la; la = la->id.next) {
 				la->att_dist = la->clipend;

source/blender/draw/engines/eevee/eevee_lightcache.c

@@ -671,6 +671,7 @@ static void eevee_lightbake_cache_create(EEVEE_Data *vedata, EEVEE_LightBake *lb
 	/* Disable all effects BUT high bitdepth shadows. */
 	scene_eval->eevee.flag &= SCE_EEVEE_SHADOW_HIGH_BITDEPTH;
 	scene_eval->eevee.taa_samples = 1;
+	scene_eval->eevee.gi_irradiance_smoothing = 0.0f;
 
 	stl->g_data = MEM_callocN(sizeof(*stl->g_data), __func__);
 	stl->g_data->background_alpha = 1.0f;

source/blender/draw/engines/eevee/eevee_lightprobes.c

@@ -833,6 +833,8 @@ void EEVEE_lightprobes_cache_finish(EEVEE_ViewLayerData *sldata, EEVEE_Data *ved
 	EEVEE_StorageList *stl = vedata->stl;
 	LightCache *light_cache = stl->g_data->light_cache;
 	EEVEE_LightProbesInfo *pinfo = sldata->probes;
+	const DRWContextState *draw_ctx = DRW_context_state_get();
+	const Scene *scene_eval = DEG_get_evaluated_scene(draw_ctx->depsgraph);
 
 	eevee_lightprobes_extract_from_cache(sldata->probes, light_cache);
 
@@ -843,6 +845,7 @@ void EEVEE_lightprobes_cache_finish(EEVEE_ViewLayerData *sldata, EEVEE_Data *ved
 	sldata->common_data.prb_lod_cube_max = (float)light_cache->mips_len - 1.0f;
 	sldata->common_data.prb_lod_planar_max = (float)MAX_PLANAR_LOD_LEVEL;
 	sldata->common_data.prb_irradiance_vis_size = light_cache->vis_res;
+	sldata->common_data.prb_irradiance_smooth = SQUARE(scene_eval->eevee.gi_irradiance_smoothing);
 	sldata->common_data.prb_num_render_cube = max_ii(1, light_cache->cube_len);
 	sldata->common_data.prb_num_render_grid = max_ii(1, light_cache->grid_len);
 	sldata->common_data.prb_num_planar = pinfo->num_planar;
@@ -859,7 +862,6 @@ void EEVEE_lightprobes_cache_finish(EEVEE_ViewLayerData *sldata, EEVEE_Data *ved
 	if (!DRW_state_is_image_render() && !DRW_state_is_opengl_render() &&
 	    (pinfo->do_grid_update || pinfo->do_cube_update))
 	{
-		const DRWContextState *draw_ctx = DRW_context_state_get();
 		BLI_assert(draw_ctx->evil_C);
 
 		if (draw_ctx->scene->eevee.flag & SCE_EEVEE_GI_AUTOBAKE) {

source/blender/draw/engines/eevee/eevee_private.h

@@ -653,6 +653,7 @@ typedef struct EEVEE_CommonUniformBuffer {
 	int prb_num_render_cube; /* int */
 	int prb_num_render_grid; /* int */
 	int prb_irradiance_vis_size; /* int */
+	float prb_irradiance_smooth; /* float */
 	float prb_lod_cube_max; /* float */
 	float prb_lod_planar_max; /* float */
 	/* Misc */

source/blender/draw/engines/eevee/shaders/common_uniforms_lib.glsl

@@ -34,6 +34,7 @@ layout(std140) uniform common_block {
 	int prbNumRenderCube;
 	int prbNumRenderGrid;
 	int prbIrradianceVisSize;
+	float prbIrradianceSmooth;
 	float prbLodCubeMax;
 	float prbLodPlanarMax;
 	/* Misc*/

source/blender/draw/engines/eevee/shaders/lightprobe_lib.glsl

@@ -273,14 +273,18 @@ vec3 probe_evaluate_grid(GridData gd, vec3 W, vec3 N, vec3 localpos)
 		float ws_dist_point_to_cell = length(ws_point_to_cell);
 		vec3 ws_light = ws_point_to_cell / ws_dist_point_to_cell;
 
-		vec3 trilinear = mix(1 - trilinear_weight, trilinear_weight, offset);
-		float weight = trilinear.x * trilinear.y * trilinear.z;
+		/* Smooth backface test */
+		float weight = saturate(dot(ws_light, N));
 
 		/* Precomputed visibility */
 		weight *= load_visibility_cell(cell, ws_light, ws_dist_point_to_cell, gd.g_vis_bias, gd.g_vis_bleed, gd.g_vis_range);
 
-		/* Smooth backface test */
-		weight *= dot(ws_light, N);
+		/* Smoother transition */
+		weight += prbIrradianceSmooth;
+
+		/* Trilinear weights */
+		vec3 trilinear = mix(1.0 - trilinear_weight, trilinear_weight, offset);
+		weight *= trilinear.x * trilinear.y * trilinear.z;
 
 		/* Avoid zero weight */
 		weight = max(0.00001, weight);

source/blender/makesdna/DNA_scene_types.h

@@ -1460,6 +1460,8 @@ typedef struct SceneEEVEE {
 	int gi_diffuse_bounces;
 	int gi_cubemap_resolution;
 	int gi_visibility_resolution;
+	float gi_irradiance_smoothing;
+	float pad;
 
 	float gi_cubemap_draw_size;
 	float gi_irradiance_draw_size;

source/blender/makesrna/intern/rna_scene.c

@@ -5682,6 +5682,12 @@ static void rna_def_scene_eevee(BlenderRNA *brna)
 	                               "Size of the shadow map applied to each irradiance sample");
 	RNA_def_property_override_flag(prop, PROPOVERRIDE_OVERRIDABLE_STATIC);
 
+	prop = RNA_def_property(srna, "gi_irradiance_smoothing", PROP_FLOAT, PROP_FACTOR);
+	RNA_def_property_range(prop, 0.0f, FLT_MAX);
+	RNA_def_property_ui_range(prop, 0.0f, 1.0f, 5, 2);
+	RNA_def_property_float_default(prop, 0.1f);
+	RNA_def_property_ui_text(prop, "Irradiance Smoothing", "Smoother irradiance interpolation but introduce light bleeding");
+
 	prop = RNA_def_property(srna, "gi_show_irradiance", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", SCE_EEVEE_SHOW_IRRADIANCE);
 	RNA_def_property_boolean_default(prop, 0);