Eevee: SSR: Refactor multiple rays. Plus other changes...temp-ssr

-Allow a maximum of 4 rays per trace pixel.
-Removes parameter Normalize: use normalization all the time now.
-Add firefly clamp slider.

9 files changed, 194 insertions, 207 deletions

diff --git a/release/scripts/startup/bl_ui/properties_render.py b/release/scripts/startup/bl_ui/properties_render.py
index 136ee3732ff..f35b3a5f47d 100644
--- a/release/scripts/startup/bl_ui/properties_render.py
+++ b/release/scripts/startup/bl_ui/properties_render.py
@@ -710,8 +710,8 @@ class RENDER_PT_eevee_volumetric(RenderButtonsPanel, Panel):
         col.prop(props, "volumetric_colored_transmittance")
 
 
-class RENDER_PT_eevee_shading(RenderButtonsPanel, Panel):
-    bl_label = "Shading"
+class RENDER_PT_eevee_screen_space_reflections(RenderButtonsPanel, Panel):
+    bl_label = "Screen Space Reflections"
     COMPAT_ENGINES = {'BLENDER_EEVEE'}
 
     @classmethod
@@ -719,19 +719,23 @@ class RENDER_PT_eevee_shading(RenderButtonsPanel, Panel):
         scene = context.scene
         return scene and (scene.render.engine in cls.COMPAT_ENGINES)
 
+    def draw_header(self, context):
+        scene = context.scene
+        props = scene.layer_properties['BLENDER_EEVEE']
+        self.layout.prop(props, "ssr_enable", text="")
+
     def draw(self, context):
         layout = self.layout
         scene = context.scene
         props = scene.layer_properties['BLENDER_EEVEE']
 
         col = layout.column()
-        col.prop(props, "ssr_enable")
         col.prop(props, "ssr_halfres")
-        col.prop(props, "ssr_two_rays")
-        col.prop(props, "ssr_normalize_weight")
+        col.prop(props, "ssr_ray_count")
         col.prop(props, "ssr_stride")
         col.prop(props, "ssr_thickness")
         col.prop(props, "ssr_border_fade")
+        col.prop(props, "ssr_firefly_fac")
 
 
 classes = (
@@ -751,10 +755,10 @@ classes = (
     RENDER_PT_bake,
     RENDER_PT_clay_layer_settings,
     RENDER_PT_clay_collection_settings,
+    RENDER_PT_eevee_volumetric,
+    RENDER_PT_eevee_screen_space_reflections,
     RENDER_PT_eevee_poststack_settings,
     RENDER_PT_eevee_postprocess_settings,
-    RENDER_PT_eevee_volumetric,
-    RENDER_PT_eevee_shading,
 )
 
 if __name__ == "__main__":  # only for live edit.
diff --git a/release/scripts/startup/bl_ui/properties_render_layer.py b/release/scripts/startup/bl_ui/properties_render_layer.py
index d5a56fbf84e..5aeb117c071 100644
--- a/release/scripts/startup/bl_ui/properties_render_layer.py
+++ b/release/scripts/startup/bl_ui/properties_render_layer.py
@@ -250,8 +250,8 @@ class RENDERLAYER_PT_eevee_volumetric(RenderLayerButtonsPanel, Panel):
         col.template_override_property(layer_props, scene_props, "volumetric_colored_transmittance")
 
 
-class RENDERLAYER_PT_eevee_shading(RenderLayerButtonsPanel, Panel):
-    bl_label = "Shading"
+class RENDERLAYER_PT_eevee_screen_space_reflections(RenderLayerButtonsPanel, Panel):
+    bl_label = "Screen Space Reflections"
     COMPAT_ENGINES = {'BLENDER_EEVEE'}
 
     @classmethod
@@ -259,6 +259,14 @@ class RENDERLAYER_PT_eevee_shading(RenderLayerButtonsPanel, Panel):
         scene = context.scene
         return scene and (scene.render.engine in cls.COMPAT_ENGINES)
 
+    def draw_header(self, context):
+        scene = context.scene
+        scene_props = scene.layer_properties['BLENDER_EEVEE']
+        layer = bpy.context.render_layer
+        layer_props = layer.engine_overrides['BLENDER_EEVEE']
+
+        self.layout.template_override_property(layer_props, scene_props, "ssr_enable", text="")
+
     def draw(self, context):
         layout = self.layout
         scene = context.scene
@@ -267,13 +275,12 @@ class RENDERLAYER_PT_eevee_shading(RenderLayerButtonsPanel, Panel):
         layer_props = layer.engine_overrides['BLENDER_EEVEE']
 
         col = layout.column()
-        col.template_override_property(layer_props, scene_props, "ssr_enable")
         col.template_override_property(layer_props, scene_props, "ssr_halfres")
-        col.template_override_property(layer_props, scene_props, "ssr_two_rays")
-        col.template_override_property(layer_props, scene_props, "ssr_normalize_weight")
+        col.template_override_property(layer_props, scene_props, "ssr_ray_count")
         col.template_override_property(layer_props, scene_props, "ssr_stride")
         col.template_override_property(layer_props, scene_props, "ssr_thickness")
         col.template_override_property(layer_props, scene_props, "ssr_border_fade")
+        col.template_override_property(layer_props, scene_props, "ssr_firefly_fac")
 
 
 classes = (
@@ -284,7 +291,7 @@ classes = (
     RENDERLAYER_PT_clay_settings,
     RENDERLAYER_PT_eevee_poststack_settings,
     RENDERLAYER_PT_eevee_postprocess_settings,
-    RENDERLAYER_PT_eevee_shading,
+    RENDERLAYER_PT_eevee_screen_space_reflections,
     RENDERLAYER_PT_eevee_volumetric,
 )
 
diff --git a/source/blender/draw/engines/eevee/eevee_effects.c b/source/blender/draw/engines/eevee/eevee_effects.c
index 34b33598a56..6a7983b71a6 100644
--- a/source/blender/draw/engines/eevee/eevee_effects.c
+++ b/source/blender/draw/engines/eevee/eevee_effects.c
@@ -59,10 +59,8 @@ typedef struct EEVEE_LightProbeData {
 /* SSR shader variations */
 enum {
 	SSR_RESOLVE      = (1 << 0),
-	SSR_TWO_HIT      = (1 << 1),
-	SSR_FULL_TRACE   = (1 << 2),
-	SSR_NORMALIZE    = (1 << 3),
-	SSR_MAX_SHADER   = (1 << 4),
+	SSR_FULL_TRACE   = (1 << 1),
+	SSR_MAX_SHADER   = (1 << 2),
 };
 
 static struct {
@@ -194,15 +192,9 @@ static struct GPUShader *eevee_effects_ssr_shader_get(int options)
 		else {
 			BLI_dynstr_appendf(ds_defines, "#define STEP_RAYTRACE\n");
 		}
-		if (options & SSR_TWO_HIT) {
-			BLI_dynstr_appendf(ds_defines, "#define TWO_HIT\n");
-		}
 		if (options & SSR_FULL_TRACE) {
 			BLI_dynstr_appendf(ds_defines, "#define FULLRES\n");
 		}
-		if (options & SSR_NORMALIZE) {
-			BLI_dynstr_appendf(ds_defines, "#define USE_NORMALIZATION\n");
-		}
 		char *ssr_define_str = BLI_dynstr_get_cstring(ds_defines);
 		BLI_dynstr_free(ds_defines);
 
@@ -581,12 +573,16 @@ void EEVEE_effects_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *vedata)
 		/* Enable double buffering to be able to read previous frame color */
 		effects->enabled_effects |= EFFECT_DOUBLE_BUFFER;
 
-		effects->ssr_use_two_hit = BKE_collection_engine_property_value_get_bool(props, "ssr_two_rays");
+		effects->ssr_ray_count = BKE_collection_engine_property_value_get_int(props, "ssr_ray_count");
 		effects->reflection_trace_full = !BKE_collection_engine_property_value_get_bool(props, "ssr_halfres");
 		effects->ssr_use_normalization = BKE_collection_engine_property_value_get_bool(props, "ssr_normalize_weight");
 		effects->ssr_stride = (float)BKE_collection_engine_property_value_get_int(props, "ssr_stride");
 		effects->ssr_thickness = BKE_collection_engine_property_value_get_float(props, "ssr_thickness");
 		effects->ssr_border_fac = BKE_collection_engine_property_value_get_float(props, "ssr_border_fade");
+		effects->ssr_firefly_fac = BKE_collection_engine_property_value_get_float(props, "ssr_firefly_fac");
+
+		/* Important, can lead to breakage otherwise. */
+		CLAMP(effects->ssr_ray_count, 1, 4);
 
 		const int divisor = (effects->reflection_trace_full) ? 1 : 2;
 		int tracing_res[2] = {(int)viewport_size[0] / divisor, (int)viewport_size[1] / divisor};
@@ -613,10 +609,12 @@ void EEVEE_effects_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *vedata)
 
 		/* Raytracing output */
 		/* TODO try integer format for hit coord to increase precision */
-		DRWFboTexture tex_output[2] = {{&stl->g_data->ssr_hit_output, (effects->ssr_use_two_hit) ? DRW_TEX_RGBA_16 : DRW_TEX_RG_16, DRW_TEX_TEMP},
-		                               {&stl->g_data->ssr_pdf_output, (effects->ssr_use_two_hit) ? DRW_TEX_RG_16 : DRW_TEX_R_16, DRW_TEX_TEMP}};
+		DRWFboTexture tex_output[4] = {{&stl->g_data->ssr_hit_output[0], DRW_TEX_RGBA_16, DRW_TEX_TEMP},
+		                               {&stl->g_data->ssr_hit_output[1], DRW_TEX_RGBA_16, DRW_TEX_TEMP},
+		                               {&stl->g_data->ssr_hit_output[2], DRW_TEX_RGBA_16, DRW_TEX_TEMP},
+		                               {&stl->g_data->ssr_hit_output[3], DRW_TEX_RGBA_16, DRW_TEX_TEMP}};
 
-		DRW_framebuffer_init(&fbl->screen_tracing_fb, &draw_engine_eevee_type, tracing_res[0], tracing_res[1], tex_output, 2);
+		DRW_framebuffer_init(&fbl->screen_tracing_fb, &draw_engine_eevee_type, tracing_res[0], tracing_res[1], tex_output, effects->ssr_ray_count);
 
 		/* Compute pixel projection matrix */
 		{
@@ -641,8 +639,9 @@ void EEVEE_effects_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *vedata)
 		DRW_TEXTURE_FREE_SAFE(txl->ssr_normal_input);
 		DRW_TEXTURE_FREE_SAFE(txl->ssr_specrough_input);
 		DRW_FRAMEBUFFER_FREE_SAFE(fbl->screen_tracing_fb);
-		stl->g_data->ssr_hit_output = NULL;
-		stl->g_data->ssr_pdf_output = NULL;
+		for (int i = 0; i < 4; ++i) {
+			stl->g_data->ssr_hit_output[i] = NULL;
+		}
 	}
 
 	/* Setup double buffer so we can access last frame as it was before post processes */
@@ -747,10 +746,7 @@ void EEVEE_effects_cache_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *vedata)
 	}
 
 	if ((effects->enabled_effects & EFFECT_SSR) != 0) {
-		int options = 0;
-		options |= (effects->ssr_use_two_hit) ? SSR_TWO_HIT : 0;
-		options |= (effects->reflection_trace_full) ? SSR_FULL_TRACE : 0;
-		options |= (effects->ssr_use_normalization) ? SSR_NORMALIZE : 0;
+		int options = (effects->reflection_trace_full) ? SSR_FULL_TRACE : 0;
 
 		struct GPUShader *trace_shader = eevee_effects_ssr_shader_get(options);
 		struct GPUShader *resolve_shader = eevee_effects_ssr_shader_get(SSR_RESOLVE | options);
@@ -764,6 +760,7 @@ void EEVEE_effects_cache_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *vedata)
 		DRW_shgroup_uniform_vec4(grp, "viewvecs[0]", (float *)stl->g_data->viewvecs, 2);
 		DRW_shgroup_uniform_vec2(grp, "ssrParameters", &effects->ssr_stride, 1);
 		DRW_shgroup_uniform_mat4(grp, "PixelProjMatrix", (float *)&e_data.pixelprojmat);
+		DRW_shgroup_uniform_int(grp, "rayCount", &effects->ssr_ray_count, 1);
 		DRW_shgroup_call_add(grp, quad, NULL);
 
 		psl->ssr_resolve = DRW_pass_create("SSR Resolve", DRW_STATE_WRITE_COLOR | DRW_STATE_ADDITIVE);
@@ -773,18 +770,22 @@ void EEVEE_effects_cache_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *vedata)
 		DRW_shgroup_uniform_buffer(grp, "specroughBuffer", &txl->ssr_specrough_input);
 		DRW_shgroup_uniform_texture(grp, "utilTex", EEVEE_materials_get_util_tex());
 		DRW_shgroup_uniform_buffer(grp, "colorBuffer", &txl->color_double_buffer);
-		DRW_shgroup_uniform_buffer(grp, "hitBuffer", &stl->g_data->ssr_hit_output);
-		DRW_shgroup_uniform_buffer(grp, "pdfBuffer", &stl->g_data->ssr_pdf_output);
 		DRW_shgroup_uniform_mat4(grp, "PastViewProjectionMatrix", (float *)stl->g_data->prev_persmat);
 		DRW_shgroup_uniform_vec4(grp, "viewvecs[0]", (float *)stl->g_data->viewvecs, 2);
 		DRW_shgroup_uniform_int(grp, "probe_count", &sldata->probes->num_render_cube, 1);
 		DRW_shgroup_uniform_float(grp, "borderFadeFactor", &effects->ssr_border_fac, 1);
 		DRW_shgroup_uniform_float(grp, "lodCubeMax", &sldata->probes->lod_cube_max, 1);
 		DRW_shgroup_uniform_float(grp, "lodPlanarMax", &sldata->probes->lod_planar_max, 1);
+		DRW_shgroup_uniform_float(grp, "fireflyFactor", &effects->ssr_firefly_fac, 1);
 		DRW_shgroup_uniform_block(grp, "probe_block", sldata->probe_ubo);
 		DRW_shgroup_uniform_block(grp, "planar_block", sldata->planar_ubo);
 		DRW_shgroup_uniform_buffer(grp, "probeCubes", &sldata->probe_pool);
 		DRW_shgroup_uniform_buffer(grp, "probePlanars", &vedata->txl->planar_pool);
+		DRW_shgroup_uniform_buffer(grp, "hitBuffer0", &stl->g_data->ssr_hit_output[0]);
+		DRW_shgroup_uniform_buffer(grp, "hitBuffer1", (effects->ssr_ray_count < 2) ? &stl->g_data->ssr_hit_output[0] : &stl->g_data->ssr_hit_output[1]);
+		DRW_shgroup_uniform_buffer(grp, "hitBuffer2", (effects->ssr_ray_count < 3) ? &stl->g_data->ssr_hit_output[0] : &stl->g_data->ssr_hit_output[2]);
+		DRW_shgroup_uniform_buffer(grp, "hitBuffer3", (effects->ssr_ray_count < 4) ? &stl->g_data->ssr_hit_output[0] : &stl->g_data->ssr_hit_output[3]);
+		DRW_shgroup_uniform_int(grp, "rayCount", &effects->ssr_ray_count, 1);
 		DRW_shgroup_call_add(grp, quad, NULL);
 	}
 
@@ -1063,8 +1064,9 @@ void EEVEE_effects_do_ssr(EEVEE_SceneLayerData *UNUSED(sldata), EEVEE_Data *veda
 		DefaultTextureList *dtxl = DRW_viewport_texture_list_get();
 		e_data.depth_src = dtxl->depth;
 
-		DRW_framebuffer_texture_attach(fbl->screen_tracing_fb, stl->g_data->ssr_hit_output, 0, 0);
-		DRW_framebuffer_texture_attach(fbl->screen_tracing_fb, stl->g_data->ssr_pdf_output, 1, 0);
+		for (int i = 0; i < effects->ssr_ray_count; ++i) {
+			DRW_framebuffer_texture_attach(fbl->screen_tracing_fb, stl->g_data->ssr_hit_output[i], i, 0);
+		}
 		DRW_framebuffer_bind(fbl->screen_tracing_fb);
 
 		if (stl->g_data->valid_double_buffer) {
@@ -1072,12 +1074,13 @@ void EEVEE_effects_do_ssr(EEVEE_SceneLayerData *UNUSED(sldata), EEVEE_Data *veda
 			DRW_draw_pass(psl->ssr_raytrace);
 		}
 		else {
-			float clear_col[4] = {-1.0f, -1.0f, -1.0f, -1.0f};
+			float clear_col[4] = {0.0f, 0.0f, -1.0f, 0.001f};
 			DRW_framebuffer_clear(true, false, false, clear_col, 0.0f);
 		}
 
-		DRW_framebuffer_texture_detach(stl->g_data->ssr_hit_output);
-		DRW_framebuffer_texture_detach(stl->g_data->ssr_pdf_output);
+		for (int i = 0; i < effects->ssr_ray_count; ++i) {
+			DRW_framebuffer_texture_detach(stl->g_data->ssr_hit_output[i]);
+		}
 
 		EEVEE_downsample_buffer(vedata, fbl->downsample_fb, txl->color_double_buffer, 9);
 
@@ -1239,24 +1242,21 @@ void EEVEE_draw_effects(EEVEE_Data *vedata)
 	DRW_transform_to_display(effects->source_buffer);
 
 	/* Debug : Ouput buffer to view. */
-	if ((G.debug_value > 0) && (G.debug_value <= 6)) {
+	if ((G.debug_value > 0) && (G.debug_value <= 5)) {
 		switch (G.debug_value) {
 			case 1:
 				if (stl->g_data->minzbuffer) DRW_transform_to_display(stl->g_data->minzbuffer);
 				break;
 			case 2:
-				if (stl->g_data->ssr_hit_output) DRW_transform_to_display(stl->g_data->ssr_hit_output);
+				if (stl->g_data->ssr_hit_output[0]) DRW_transform_to_display(stl->g_data->ssr_hit_output[0]);
 				break;
 			case 3:
-				if (stl->g_data->ssr_pdf_output) DRW_transform_to_display(stl->g_data->ssr_pdf_output);
-				break;
-			case 4:
 				if (txl->ssr_normal_input) DRW_transform_to_display(txl->ssr_normal_input);
 				break;
-			case 5:
+			case 4:
 				if (txl->ssr_specrough_input) DRW_transform_to_display(txl->ssr_specrough_input);
 				break;
-			case 6:
+			case 5:
 				if (txl->color_double_buffer) DRW_transform_to_display(txl->color_double_buffer);
 				break;
 			default:
diff --git a/source/blender/draw/engines/eevee/eevee_engine.c b/source/blender/draw/engines/eevee/eevee_engine.c
index 74b1280ff56..3e2408034d7 100644
--- a/source/blender/draw/engines/eevee/eevee_engine.c
+++ b/source/blender/draw/engines/eevee/eevee_engine.c
@@ -208,12 +208,12 @@ static void EEVEE_scene_layer_settings_create(RenderEngine *UNUSED(engine), IDPr
 	           props->subtype == IDP_GROUP_SUB_ENGINE_RENDER);
 
 	BKE_collection_engine_property_add_bool(props, "ssr_enable", false);
-	BKE_collection_engine_property_add_bool(props, "ssr_two_rays", false);
-	BKE_collection_engine_property_add_bool(props, "ssr_normalize_weight", false);
 	BKE_collection_engine_property_add_bool(props, "ssr_halfres", true);
+	BKE_collection_engine_property_add_int(props, "ssr_ray_count", 1);
 	BKE_collection_engine_property_add_int(props, "ssr_stride", 16);
 	BKE_collection_engine_property_add_float(props, "ssr_thickness", 0.2f);
 	BKE_collection_engine_property_add_float(props, "ssr_border_fade", 0.075f);
+	BKE_collection_engine_property_add_float(props, "ssr_firefly_fac", 0.5f);
 
 	BKE_collection_engine_property_add_bool(props, "volumetric_enable", false);
 	BKE_collection_engine_property_add_float(props, "volumetric_start", 0.1f);
diff --git a/source/blender/draw/engines/eevee/eevee_lightprobes.c b/source/blender/draw/engines/eevee/eevee_lightprobes.c
index d5986cb7e03..c5b1966f9da 100644
--- a/source/blender/draw/engines/eevee/eevee_lightprobes.c
+++ b/source/blender/draw/engines/eevee/eevee_lightprobes.c
@@ -1052,7 +1052,6 @@ static void render_scene_to_planar(
 	EEVEE_FramebufferList *fbl = vedata->fbl;
 	EEVEE_TextureList *txl = vedata->txl;
 	EEVEE_PassList *psl = vedata->psl;
-	EEVEE_StorageList *stl = vedata->stl;
 
 	float viewinv[4][4];
 	float persinv[4][4];
diff --git a/source/blender/draw/engines/eevee/eevee_private.h b/source/blender/draw/engines/eevee/eevee_private.h
index ae928cf0dbb..55fb550d940 100644
--- a/source/blender/draw/engines/eevee/eevee_private.h
+++ b/source/blender/draw/engines/eevee/eevee_private.h
@@ -322,8 +322,9 @@ typedef struct EEVEE_EffectsInfo {
 	/* SSR */
 	bool use_ssr;
 	bool reflection_trace_full;
-	bool ssr_use_two_hit;
 	bool ssr_use_normalization;
+	int ssr_ray_count;
+	float ssr_firefly_fac;
 	float ssr_border_fac;
 	float ssr_stride;
 	float ssr_thickness;
@@ -459,8 +460,7 @@ typedef struct EEVEE_PrivateData {
 	struct GHash *material_hash;
 	struct GHash *hair_material_hash;
 	struct GPUTexture *minzbuffer;
-	struct GPUTexture *ssr_hit_output;
-	struct GPUTexture *ssr_pdf_output;
+	struct GPUTexture *ssr_hit_output[4];
 	struct GPUTexture *volumetric;
 	struct GPUTexture *volumetric_transmit;
 	float background_alpha; /* TODO find a better place for this. */
diff --git a/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl b/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl
index 268afa1e373..7b516f27ec9 100644
--- a/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/effect_ssr_frag.glsl
@@ -1,9 +1,14 @@
 
+/* Based on Stochastic Screen Space Reflections
+ * https://www.ea.com/frostbite/news/stochastic-screen-space-reflections */
+
 #ifndef UTIL_TEX
 #define UTIL_TEX
 uniform sampler2DArray utilTex;
 #endif /* UTIL_TEX */
 
+uniform int rayCount;
+
 #define BRDF_BIAS 0.7
 
 vec3 generate_ray(vec3 V, vec3 N, float a2, vec3 rand, out float pdf)
@@ -15,6 +20,7 @@ vec3 generate_ray(vec3 V, vec3 N, float a2, vec3 rand, out float pdf)
 	/* Importance sampling bias */
 	rand.x = mix(rand.x, 0.0, BRDF_BIAS);
 
+	/* TODO distribution of visible normals */
 	vec3 H = sample_ggx(rand, a2, N, T, B, NH); /* Microfacet normal */
 	pdf = min(1024e32, pdf_ggx_reflect(NH, a2)); /* Theoretical limit of 16bit float */
 	return reflect(-V, H);
@@ -28,8 +34,34 @@ uniform sampler2D depthBuffer;
 uniform sampler2D normalBuffer;
 uniform sampler2D specroughBuffer;
 
-layout(location = 0) out vec4 hitData;
-layout(location = 1) out vec4 pdfData;
+uniform mat4 ViewProjectionMatrix;
+
+layout(location = 0) out vec4 hitData0;
+layout(location = 1) out vec4 hitData1;
+layout(location = 2) out vec4 hitData2;
+layout(location = 3) out vec4 hitData3;
+
+bool has_hit_backface(vec3 hit_pos, vec3 R, vec3 V)
+{
+	vec2 hit_co = project_point(ProjectionMatrix, hit_pos).xy * 0.5 + 0.5;
+	vec3 hit_N = normal_decode(textureLod(normalBuffer, hit_co, 0.0).rg, V);
+	return (dot(-R, hit_N) < 0.0);
+}
+
+vec4 do_ssr(sampler2D depthBuffer, vec3 V, vec3 N, vec3 viewPosition, float a2, vec3 rand)
+{
+	float pdf;
+	vec3 R = generate_ray(V, N, a2, rand, pdf);
+
+	float hit_dist = raycast(depthBuffer, viewPosition, R, rand.x);
+	vec3 hit_pos = viewPosition + R * abs(hit_dist);
+
+	if (has_hit_backface(hit_pos, R, V) || (hit_dist <= 0.0)) {
+		hit_pos.z *= -1.0;
+	}
+
+	return vec4(hit_pos, pdf);
+}
 
 void main()
 {
@@ -68,81 +100,13 @@ void main()
 	float roughnessSquared = max(1e-3, roughness * roughness);
 	float a2 = roughnessSquared * roughnessSquared;
 
-	/* Generate Ray */
-	float pdf;
 	vec3 rand = texelFetch(utilTex, ivec3(halfres_texel % LUT_SIZE, 2), 0).rba;
-	vec3 R = generate_ray(V, N, a2, rand, pdf);
-#ifdef TWO_HIT
-	float pdf2;
-	vec3 R2 = generate_ray(V, N, a2, rand * vec3(1.0, -1.0, -1.0), pdf2);
-#endif
-
-	/* Search for the planar reflection affecting this pixel */
-	/* If no planar is found, fallback to screen space */
-
-	/* Raycast over planar reflection */
-	/* Potentially lots of time waisted here for pixels
-	 * that does not have planar reflections. TODO Profile it. */
-	/* TODO: Idea, rasterize boxes around planar
-	 * reflection volumes (frontface culling to avoid overdraw)
-	 * and do the raycasting, discard pixel that are not in influence.
-	 * Add stencil test to discard the main SSR.
-	 * Cons: - Potentially raytrace multiple times
-	 *         if Planar Influence overlaps. */
-	//float hit_dist = raycast(depthBuffer, W, R);
-
-	/* Raycast over screen */
-	float hit_dist = -1.0;
-#ifdef TWO_HIT
-	float hit_dist2 = -1.0;
-#endif
-	/* Only raytrace if ray is above the surface normal */
-	/* Note : this still fails in some cases like with normal map.
-	 * We should check against the geometric normal but we don't have it at this stage. */
-	if (dot(R, N) > 0.0001) {
-		hit_dist = raycast(depthBuffer, viewPosition, R, rand.x);
-	}
-#ifdef TWO_HIT
-	/* TODO do double raytrace at the same time */
-	if (dot(R2, N) > 0.0001) {
-		hit_dist2 = raycast(depthBuffer, viewPosition, R2, rand.x);
-	}
-#endif
-
-	/* TODO Do reprojection here */
-	vec2 hit_co = project_point(ProjectionMatrix, viewPosition + R * hit_dist).xy * 0.5 + 0.5;
-#ifdef TWO_HIT
-	vec2 hit_co2 = project_point(ProjectionMatrix, viewPosition + R2 * hit_dist2).xy * 0.5 + 0.5;
-#endif
-
-	/* Check if has hit a backface */
-	vec3 hit_N = normal_decode(textureLod(normalBuffer, hit_co, 0.0).rg, V);
-	hit_dist *= step(0.0, dot(-R, hit_N));
-#ifdef TWO_HIT
-	hit_N = normal_decode(textureLod(normalBuffer, hit_co2, 0.0).rg, V);
-	hit_dist2 *= step(0.0, dot(-R2, hit_N));
-#endif
-
-	if (hit_dist > 0.0) {
-		hitData = hit_co.xyxy;
-	}
-	else {
-		hitData = vec4(-1.0);
-	}
-#ifdef TWO_HIT
-	if (hit_dist2 > 0.0) {
-		hitData.zw = hit_co2;
-	}
-	else {
-		hitData.zw = vec2(-1.0);
-	}
-#endif
 
-#ifdef TWO_HIT
-	pdfData = vec4(pdf, pdf2, 0.0, 0.0);
-#else
-	pdfData = vec4(pdf);
-#endif
+	/* TODO : Raytrace together if textureGather is supported. */
+	hitData0 = do_ssr(depthBuffer, V, N, viewPosition, a2, rand);
+	if (rayCount > 1) hitData1 = do_ssr(depthBuffer, V, N, viewPosition, a2, rand.xyz * vec3(1.0, -1.0, -1.0));
+	if (rayCount > 2) hitData2 = do_ssr(depthBuffer, V, N, viewPosition, a2, rand.xzy * vec3(1.0,  1.0, -1.0));
+	if (rayCount > 3) hitData3 = do_ssr(depthBuffer, V, N, viewPosition, a2, rand.xzy * vec3(1.0, -1.0,  1.0));
 }
 
 #else /* STEP_RESOLVE */
@@ -152,12 +116,15 @@ uniform sampler2D depthBuffer;
 uniform sampler2D normalBuffer;
 uniform sampler2D specroughBuffer;
 
-uniform sampler2D hitBuffer;
-uniform sampler2D pdfBuffer;
+uniform sampler2D hitBuffer0;
+uniform sampler2D hitBuffer1;
+uniform sampler2D hitBuffer2;
+uniform sampler2D hitBuffer3;
 
 uniform int probe_count;
 
 uniform float borderFadeFactor;
+uniform float fireflyFactor;
 
 uniform mat4 ViewProjectionMatrix;
 uniform mat4 PastViewProjectionMatrix;
@@ -218,19 +185,6 @@ float brightness(vec3 c)
 	return max(max(c.r, c.g), c.b);
 }
 
-vec2 get_reprojected_reflection(vec3 hit, vec3 pos, vec3 N)
-{
-	/* TODO real motion vectors */
-	/* Transform to viewspace */
-	// vec4(get_view_space_from_depth(uvcoords, depth), 1.0);
-	// vec4(get_view_space_from_depth(uvcoords, depth), 1.0);
-
-	/* Reproject */
-	// vec3 hit_reprojected = find_reflection_incident_point(cameraPos, hit, pos, N);
-
-	return project_point(PastViewProjectionMatrix, hit).xy * 0.5 + 0.5;
-}
-
 float screen_border_mask(vec2 past_hit_co, vec3 hit)
 {
 	/* Fade on current and past screen edges */
@@ -254,44 +208,51 @@ float view_facing_mask(vec3 V, vec3 R)
 	return smoothstep(0.95, 0.80, dot(V, R));
 }
 
+vec2 get_reprojected_reflection(vec3 hit, vec3 pos, vec3 N)
+{
+	/* TODO real reprojection with motion vectors, etc... */
+	return project_point(PastViewProjectionMatrix, hit).xy * 0.5 + 0.5;
+}
+
 vec4 get_ssr_sample(
-        vec2 hit_co, vec3 worldPosition, vec3 N, vec3 V, float roughnessSquared,
+        sampler2D hitBuffer, vec3 worldPosition, vec3 N, vec3 V, float roughnessSquared,
         float cone_tan, vec2 source_uvs, vec2 texture_size, ivec2 target_texel,
-        out float weight)
+        inout float weight_acc)
 {
-	/* Reconstruct ray */
-	float hit_depth = textureLod(depthBuffer, hit_co, 0.0).r;
-	vec3 hit_pos = get_world_space_from_depth(hit_co, hit_depth);
+	vec4 hit_co_pdf = texelFetch(hitBuffer, target_texel, 0).rgba;
+	bool has_hit = (hit_co_pdf.z < 0.0);
+	hit_co_pdf.z = -abs(hit_co_pdf.z);
 
-	/* Find hit position in previous frame */
+	/* Hit position in world space. */
+	vec3 hit_pos = (ViewMatrixInverse * vec4(hit_co_pdf.xyz, 1.0)).xyz;
+
+	/* Find hit position in previous frame. */
 	vec2 ref_uvs = get_reprojected_reflection(hit_pos, worldPosition, N);
 
-	/* Estimate a cone footprint to sample a corresponding mipmap level */
-	/* compute cone footprint Using UV distance because we are using screen space filtering */
+	/* Estimate a cone footprint to sample a corresponding mipmap level. */
+	/* Compute cone footprint Using UV distance because we are using screen space filtering. */
 	float cone_footprint = 1.5 * cone_tan * distance(ref_uvs, source_uvs);
 	float mip = BRDF_BIAS * clamp(log2(cone_footprint * max(texture_size.x, texture_size.y)), 0.0, MAX_MIP);
 
+	/* Slide 54 */
 	vec3 L = normalize(hit_pos - worldPosition);
-#ifdef USE_NORMALIZATION
-	/* Evaluate BSDF */
 	float bsdf = bsdf_ggx(N, L, V, roughnessSquared);
-	float pdf = texelFetch(pdfBuffer, target_texel, 0).r;
+	float weight = step(0.001, hit_co_pdf.w) * bsdf / hit_co_pdf.w;
+	weight_acc += weight;
 
-	weight = step(0.001, pdf) * bsdf / pdf;
-#else
-	weight = 1.0;
-#endif
+	vec3 sample = textureLod(colorBuffer, ref_uvs, mip).rgb;
 
-	vec3 sample = textureLod(colorBuffer, ref_uvs, mip).rgb ;
+	/* Do not add light if ray has failed. */
+	sample *= float(has_hit);
 
 	/* Firefly removal */
-	sample /= 1.0 + brightness(sample);
+	sample /= 1.0 + fireflyFactor * brightness(sample);
 
 	float mask = screen_border_mask(ref_uvs, hit_pos);
 	mask *= view_facing_mask(V, N);
+	mask *= float(has_hit);
 
-	/* Check if there was a hit */
-	return vec4(sample, mask) * weight * step(0.0, hit_co.x);
+	return vec4(sample, mask) * weight;
 }
 
 #define NUM_NEIGHBORS 9
@@ -341,34 +302,40 @@ void main()
 	float weight_acc = 0.0;
 	const ivec2 neighbors[9] = ivec2[9](
 		ivec2(0, 0),
-		ivec2(-1,  1), ivec2(0,  1), ivec2(1,  1),
-		ivec2(-1,  0),               ivec2(1,  0),
-		ivec2(-1, -1), ivec2(0, -1), ivec2(1, -1)
+
+		               ivec2(0,  1),
+		ivec2(-1, -1),               ivec2(1, -1),
+
+		ivec2(-1,  1),               ivec2(1,  1),
+		               ivec2(0, -1),
+
+		ivec2(-1,  0),               ivec2(1,  0)
 	);
 	ivec2 invert_neighbor;
 	invert_neighbor.x = ((fullres_texel.x & 0x1) == 0) ? 1 : -1;
 	invert_neighbor.y = ((fullres_texel.y & 0x1) == 0) ? 1 : -1;
+
 	for (int i = 0; i < NUM_NEIGHBORS; i++) {
 		ivec2 target_texel = halfres_texel + neighbors[i] * invert_neighbor;
 
-#ifdef TWO_HIT
-		vec4 hit_co = texelFetch(hitBuffer, target_texel, 0).rgba;
-#else
-		vec2 hit_co = texelFetch(hitBuffer, target_texel, 0).rg;
-#endif
-
-		float weight;
-		ssr_accum += get_ssr_sample(hit_co.xy, worldPosition, N, V,
-		                            roughnessSquared, cone_tan, source_uvs,
-		                            texture_size, target_texel, weight);
-		weight_acc += weight;
-
-#ifdef TWO_HIT
-		ssr_accum += get_ssr_sample(hit_co.zw, worldPosition, N, V,
+		ssr_accum += get_ssr_sample(hitBuffer0, worldPosition, N, V,
 		                            roughnessSquared, cone_tan, source_uvs,
-		                            texture_size, target_texel, weight);
-		weight_acc += weight;
-#endif
+		                            texture_size, target_texel, weight_acc);
+		if (rayCount > 1) {
+			ssr_accum += get_ssr_sample(hitBuffer1, worldPosition, N, V,
+			                            roughnessSquared, cone_tan, source_uvs,
+			                            texture_size, target_texel, weight_acc);
+		}
+		if (rayCount > 2) {
+			ssr_accum += get_ssr_sample(hitBuffer2, worldPosition, N, V,
+			                            roughnessSquared, cone_tan, source_uvs,
+			                            texture_size, target_texel, weight_acc);
+		}
+		if (rayCount > 3) {
+			ssr_accum += get_ssr_sample(hitBuffer3, worldPosition, N, V,
+			                            roughnessSquared, cone_tan, source_uvs,
+			                            texture_size, target_texel, weight_acc);
+		}
 	}
 
 	/* Compute SSR contribution */
@@ -385,8 +352,6 @@ void main()
 	}
 
 	fragColor = vec4(spec_accum.rgb * speccol_roughness.rgb, 1.0);
-	// vec2 _uvs = project_point(PastViewProjectionMatrix, worldPosition).xy * 0.5 + 0.5;
-	// fragColor = vec4(textureLod(colorBuffer, _uvs, roughness * MAX_MIP).rgb, 1.0);
 }
 
 #endif
diff --git a/source/blender/draw/engines/eevee/shaders/raytrace_lib.glsl b/source/blender/draw/engines/eevee/shaders/raytrace_lib.glsl
index f017453bad0..421079c0bfa 100644
--- a/source/blender/draw/engines/eevee/shaders/raytrace_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/raytrace_lib.glsl
@@ -21,15 +21,20 @@ void swapIfBigger(inout float a, inout float b)
 	}
 }
 
-/* Return the length of the ray if there is a hit, and -1.0 if not hit occured */
+/* Return the length of the ray if there is a hit, and negate it if not hit occured */
 float raycast(sampler2D depth_texture, vec3 ray_origin, vec3 ray_dir, float ray_jitter)
 {
 	float near = get_view_z_from_depth(0.0); /* TODO optimize */
+	float far = get_view_z_from_depth(1.0); /* TODO optimize */
 
-	/* Clip ray to a near plane in 3D */
+	/* Clip ray to a near/far plane in 3D */
 	float ray_length = 1e16;
-	if ((ray_origin.z + ray_dir.z * ray_length) > near)
+	if ((ray_origin.z + ray_dir.z * ray_length) > near) {
 		ray_length = (near - ray_origin.z) / ray_dir.z;
+	}
+	else {
+		ray_length = (ray_origin.z - far) / -ray_dir.z;
+	}
 
 	vec3 ray_end = ray_dir * ray_length + ray_origin;
 
@@ -136,7 +141,7 @@ float raycast(sampler2D depth_texture, vec3 ray_origin, vec3 ray_dir, float ray_
 
 		prev_zmax = (dPQK.z * -0.5 + pqk.z) / (dPQK.w * -0.5 + pqk.w);
 
-		for (float refinestep = 0.0; refinestep < ssrStride * 2.0 && refinestep < MAX_REFINE_STEP * 2.0; refinestep++) {
+		for (float refinestep = 0.0; refinestep < (ssrStride * 2.0) && refinestep < (MAX_REFINE_STEP * 2.0); refinestep++) {
 			/* step through current cell */
 			pqk += dPQK;
 
@@ -159,9 +164,14 @@ float raycast(sampler2D depth_texture, vec3 ray_origin, vec3 ray_dir, float ray_
 		}
 	}
 
-	/* Background case. */
-	hit = hit && (raw_depth != 1.0);
+	/* If we did hit the background, get exact ray. */
+	if (raw_depth == 1.0) {
+		zmax = get_view_z_from_depth(1.0); /* TODO optimize */
+	}
+
+	hit = hit && (raw_depth != 0.0);
 
 	/* Return length */
-	return (hit) ? (zmax - ray_origin.z) / ray_dir.z : -1.0;
+	float result = (zmax - ray_origin.z) / ray_dir.z;
+	return (hit) ? result : -result;
 }
diff --git a/source/blender/makesrna/intern/rna_scene.c b/source/blender/makesrna/intern/rna_scene.c
index a3983290236..b2c1ea73f8a 100644
--- a/source/blender/makesrna/intern/rna_scene.c
+++ b/source/blender/makesrna/intern/rna_scene.c
@@ -2623,12 +2623,12 @@ RNA_LAYER_ENGINE_EEVEE_GET_SET_BOOL(volumetric_shadows)
 RNA_LAYER_ENGINE_EEVEE_GET_SET_INT(volumetric_shadow_samples)
 RNA_LAYER_ENGINE_EEVEE_GET_SET_BOOL(volumetric_colored_transmittance)
 RNA_LAYER_ENGINE_EEVEE_GET_SET_BOOL(ssr_enable)
-RNA_LAYER_ENGINE_EEVEE_GET_SET_BOOL(ssr_two_rays)
 RNA_LAYER_ENGINE_EEVEE_GET_SET_BOOL(ssr_halfres)
-RNA_LAYER_ENGINE_EEVEE_GET_SET_BOOL(ssr_normalize_weight)
+RNA_LAYER_ENGINE_EEVEE_GET_SET_INT(ssr_ray_count)
 RNA_LAYER_ENGINE_EEVEE_GET_SET_INT(ssr_stride)
 RNA_LAYER_ENGINE_EEVEE_GET_SET_FLOAT(ssr_thickness)
 RNA_LAYER_ENGINE_EEVEE_GET_SET_FLOAT(ssr_border_fade)
+RNA_LAYER_ENGINE_EEVEE_GET_SET_FLOAT(ssr_firefly_fac)
 
 /* object engine */
 RNA_LAYER_MODE_OBJECT_GET_SET_BOOL(show_wire)
@@ -6198,20 +6198,6 @@ static void rna_def_scene_layer_engine_settings_eevee(BlenderRNA *brna)
 	RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
 	RNA_def_property_update(prop, NC_SCENE | ND_LAYER_CONTENT, "rna_SceneLayerEngineSettings_update");
 
-	prop = RNA_def_property(srna, "ssr_two_rays", PROP_BOOLEAN, PROP_NONE);
-	RNA_def_property_boolean_funcs(prop, "rna_LayerEngineSettings_Eevee_ssr_two_rays_get",
-	                               "rna_LayerEngineSettings_Eevee_ssr_two_rays_set");
-	RNA_def_property_ui_text(prop, "Double Trace", "Raytrace two rays instead of just one");
-	RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
-	RNA_def_property_update(prop, NC_SCENE | ND_LAYER_CONTENT, "rna_SceneLayerEngineSettings_update");
-
-	prop = RNA_def_property(srna, "ssr_normalize_weight", PROP_BOOLEAN, PROP_NONE);
-	RNA_def_property_boolean_funcs(prop, "rna_LayerEngineSettings_Eevee_ssr_normalize_weight_get",
-	                               "rna_LayerEngineSettings_Eevee_ssr_normalize_weight_set");
-	RNA_def_property_ui_text(prop, "Weight Normalize", "Fills low resolution in reflection but exhibit harsh transition");
-	RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
-	RNA_def_property_update(prop, NC_SCENE | ND_LAYER_CONTENT, "rna_SceneLayerEngineSettings_update");
-
 	prop = RNA_def_property(srna, "ssr_stride", PROP_INT, PROP_PIXEL);
 	RNA_def_property_int_funcs(prop, "rna_LayerEngineSettings_Eevee_ssr_stride_get",
 	                               "rna_LayerEngineSettings_Eevee_ssr_stride_set", NULL);
@@ -6220,6 +6206,14 @@ static void rna_def_scene_layer_engine_settings_eevee(BlenderRNA *brna)
 	RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
 	RNA_def_property_update(prop, NC_SCENE | ND_LAYER_CONTENT, "rna_SceneLayerEngineSettings_update");
 
+	prop = RNA_def_property(srna, "ssr_ray_count", PROP_INT, PROP_NONE);
+	RNA_def_property_int_funcs(prop, "rna_LayerEngineSettings_Eevee_ssr_ray_count_get",
+	                               "rna_LayerEngineSettings_Eevee_ssr_ray_count_set", NULL);
+	RNA_def_property_ui_text(prop, "Samples", "Number of rays to trace per pixels");
+	RNA_def_property_range(prop, 1, 4);
+	RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
+	RNA_def_property_update(prop, NC_SCENE | ND_LAYER_CONTENT, "rna_SceneLayerEngineSettings_update");
+
 	prop = RNA_def_property(srna, "ssr_thickness", PROP_FLOAT, PROP_DISTANCE);
 	RNA_def_property_float_funcs(prop, "rna_LayerEngineSettings_Eevee_ssr_thickness_get",
 	                               "rna_LayerEngineSettings_Eevee_ssr_thickness_set", NULL);
@@ -6237,6 +6231,14 @@ static void rna_def_scene_layer_engine_settings_eevee(BlenderRNA *brna)
 	RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
 	RNA_def_property_update(prop, NC_SCENE | ND_LAYER_CONTENT, "rna_SceneLayerEngineSettings_update");
 
+	prop = RNA_def_property(srna, "ssr_firefly_fac", PROP_FLOAT, PROP_FACTOR);
+	RNA_def_property_float_funcs(prop, "rna_LayerEngineSettings_Eevee_ssr_firefly_fac_get",
+	                               "rna_LayerEngineSettings_Eevee_ssr_firefly_fac_set", NULL);
+	RNA_def_property_ui_text(prop, "Clamp", "Smoothly clamp pixel intensity to remove noise");
+	RNA_def_property_range(prop, 0.0f, 1.0f);
+	RNA_def_property_flag(prop, PROP_CONTEXT_UPDATE);
+	RNA_def_property_update(prop, NC_SCENE | ND_LAYER_CONTENT, "rna_SceneLayerEngineSettings_update");
+
 	/* Volumetrics */
 	prop = RNA_def_property(srna, "volumetric_enable", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_funcs(prop, "rna_LayerEngineSettings_Eevee_volumetric_enable_get",