Eevee: SSR Clamp color when blurring buffers.

This effectivly reduce firefly bleeding all over the place.
We still need the clamp in the resolve pass because the level 0 has not been clamped.
NOTE: I did not clamped each sample individually for performance BUT I did not profile it to know how much it cost.

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

@@ -815,6 +815,7 @@ void EEVEE_effects_cache_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *vedata)
 		psl->color_downsample_ps = DRW_pass_create("Downsample", DRW_STATE_WRITE_COLOR);
 		DRWShadingGroup *grp = DRW_shgroup_create(e_data.downsample_sh, psl->color_downsample_ps);
 		DRW_shgroup_uniform_buffer(grp, "source", &e_data.color_src);
+		DRW_shgroup_uniform_float(grp, "fireflyFactor", &effects->ssr_firefly_fac, 1);
 		DRW_shgroup_call_add(grp, quad, NULL);
 	}
 

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

@@ -434,6 +434,7 @@ void EEVEE_lightprobes_cache_init(EEVEE_SceneLayerData *sldata, EEVEE_Data *veda
 		struct Gwn_Batch *geom = DRW_cache_fullscreen_quad_get();
 		DRWShadingGroup *grp = stl->g_data->planar_downsample = DRW_shgroup_instance_create(e_data.probe_planar_downsample_sh, psl->probe_planar_downsample_ps, geom);
 		DRW_shgroup_uniform_buffer(grp, "source", &txl->planar_pool);
+		DRW_shgroup_uniform_float(grp, "fireflyFactor", &stl->effects->ssr_firefly_fac, 1);
 		DRW_shgroup_uniform_vec2(grp, "texelSize", stl->g_data->texel_size, 1);
 	}
 }

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

@@ -3,9 +3,15 @@
  **/
 
 uniform sampler2D source;
+uniform float fireflyFactor;
 
 out vec4 FragColor;
 
+float brightness(vec3 c)
+{
+	return max(max(c.r, c.g), c.b);
+}
+
 void main()
 {
 #if 0
@@ -23,5 +29,9 @@ void main()
 	FragColor += textureLod(source, uvs + ofs.zy, 0.0);
 	FragColor += textureLod(source, uvs + ofs.zw, 0.0);
 	FragColor *= 0.25;
+
+	/* Clamped brightness. */
+	float luma = max(1e-8, brightness(FragColor.rgb));
+	FragColor *= 1.0 - max(0.0, luma - fireflyFactor) / luma;
 #endif
 }

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

@@ -3,13 +3,18 @@
  **/
 
 uniform sampler2DArray source;
-uniform vec2 texelSize;
+uniform float fireflyFactor;
 
 in vec2 uvs;
 flat in float layer;
 
 out vec4 FragColor;
 
+float brightness(vec3 c)
+{
+	return max(max(c.r, c.g), c.b);
+}
+
 void main()
 {
 #if 0
@@ -27,5 +32,9 @@ void main()
 	FragColor += textureLod(source, vec3(uvs + ofs.zy, layer), 0.0);
 	FragColor += textureLod(source, vec3(uvs + ofs.zw, layer), 0.0);
 	FragColor *= 0.25;
+
+	/* Clamped brightness. */
+	float luma = max(1e-8, brightness(FragColor.rgb));
+	FragColor *= 1.0 - max(0.0, luma - fireflyFactor) / luma;
 #endif
 }