Improve volumetric fog and FogVolume documentation

doc/classes/Environment.xml

@@ -86,7 +86,7 @@
 			This is useful to simulate [url=https://en.wikipedia.org/wiki/Aerial_perspective]aerial perspective[/url] in large scenes with low density fog. However, it is not very useful for high-density fog, as the sky will shine through. When set to [code]1.0[/code], the fog color comes completely from the [Sky]. If set to [code]0.0[/code], aerial perspective is disabled.
 		</member>
 		<member name="fog_density" type="float" setter="set_fog_density" getter="get_fog_density" default="0.01">
-			The exponential fog density to use. Higher values result in a more dense fog.
+			The [i]exponential[/i] fog density to use. Higher values result in a more dense fog. Fog rendering is exponential as in real life.
 		</member>
 		<member name="fog_enabled" type="bool" setter="set_fog_enabled" getter="is_fog_enabled" default="false">
 			If [code]true[/code], fog effects are enabled.
@@ -292,13 +292,15 @@
 			The [Color] of the volumetric fog when interacting with lights. Mist and fog have an albedo close to [code]Color(1, 1, 1, 1)[/code] while smoke has a darker albedo.
 		</member>
 		<member name="volumetric_fog_ambient_inject" type="float" setter="set_volumetric_fog_ambient_inject" getter="get_volumetric_fog_ambient_inject" default="0.0">
-			Scales the strength of ambient light used in the volumetric fog. A value of [code]0[/code] means that ambient light will not impact the volumetric fog.
+			Scales the strength of ambient light used in the volumetric fog. A value of [code]0.0[/code] means that ambient light will not impact the volumetric fog. [member volumetric_fog_ambient_inject] has a small performance cost when set above [code]0.0[/code].
+			[b]Note:[/b] This has no visible effect if [member volumetric_fog_density] is [code]0.0[/code] or if [member volumetric_fog_albedo] is a fully black color.
 		</member>
 		<member name="volumetric_fog_anisotropy" type="float" setter="set_volumetric_fog_anisotropy" getter="get_volumetric_fog_anisotropy" default="0.2">
-			The direction of scattered light as it goes through the volumetric fog. A value close [code]1[/code] means almost all light is scattered forward. A value close to [code]0[/code] means light is scattered equally in all directions. A value close to [code]-1[/code] means light is scattered mostly backward. Fog and mist scatter light slightly forward, while smoke scatters light equally in all directions.
+			The direction of scattered light as it goes through the volumetric fog. A value close to [code]1.0[/code] means almost all light is scattered forward. A value close to [code]0.0[/code] means light is scattered equally in all directions. A value close to [code]-1.0[/code] means light is scattered mostly backward. Fog and mist scatter light slightly forward, while smoke scatters light equally in all directions.
 		</member>
 		<member name="volumetric_fog_density" type="float" setter="set_volumetric_fog_density" getter="get_volumetric_fog_density" default="0.05">
-			The base density of the volumetric fog. Set this to the lowest density you want to have globally.
+			The base [i]exponential[/i] density of the volumetric fog. Set this to the lowest density you want to have globally. [FogVolume]s can be used to add to or subtract from this density in specific areas. Fog rendering is exponential as in real life.
+			A value of [code]0.0[/code] disables global volumetric fog while allowing [FogVolume]s to display volumetric fog in specific areas.
 		</member>
 		<member name="volumetric_fog_detail_spread" type="float" setter="set_volumetric_fog_detail_spread" getter="get_volumetric_fog_detail_spread" default="2.0">
 			The distribution of size down the length of the froxel buffer. A higher value compresses the froxels closer to the camera and places more detail closer to the camera.
@@ -313,20 +315,22 @@
 			Enables the volumetric fog effect. Volumetric fog uses a screen-aligned froxel buffer to calculate accurate volumetric scattering in the short to medium range. Volumetric fog interacts with [FogVolume]s and lights to calculate localized and global fog. Volumetric fog uses a PBR single-scattering model based on extinction, scattering, and emission which it exposes to users as density, albedo, and emission.
 		</member>
 		<member name="volumetric_fog_gi_inject" type="float" setter="set_volumetric_fog_gi_inject" getter="get_volumetric_fog_gi_inject" default="1.0">
-			Scales the strength of Global Illumination used in the volumetric fog. A value of [code]0.0[/code] means that Global Illumination will not impact the volumetric fog.
+			Scales the strength of Global Illumination used in the volumetric fog's albedo color. A value of [code]0.0[/code] means that Global Illumination will not impact the volumetric fog. [member volumetric_fog_gi_inject] has a small performance cost when set above [code]0.0[/code].
+			[b]Note:[/b] This has no visible effect if [member volumetric_fog_density] is [code]0.0[/code] or if [member volumetric_fog_albedo] is a fully black color.
 			[b]Note:[/b] Only [VoxelGI] and SDFGI ([member Environment.sdfgi_enabled]) are taken into account when using [member volumetric_fog_gi_inject]. Global illumination from [LightmapGI], [ReflectionProbe] and SSIL (see [member ssil_enabled]) will be ignored by volumetric fog.
 		</member>
 		<member name="volumetric_fog_length" type="float" setter="set_volumetric_fog_length" getter="get_volumetric_fog_length" default="64.0">
-			The distance over which the volumetric fog is computed. Increase to compute fog over a greater range, decrease to add more detail when a long range is not needed. For best quality fog, keep this as low as possible.
+			The distance over which the volumetric fog is computed. Increase to compute fog over a greater range, decrease to add more detail when a long range is not needed. For best quality fog, keep this as low as possible. See also [member ProjectSettings.rendering/environment/volumetric_fog/volume_depth].
 		</member>
 		<member name="volumetric_fog_sky_affect" type="float" setter="set_volumetric_fog_sky_affect" getter="get_volumetric_fog_sky_affect" default="1.0">
 			The factor to use when affecting the sky with volumetric fog. [code]1.0[/code] means that volumetric fog can fully obscure the sky. Lower values reduce the impact of volumetric fog on sky rendering, with [code]0.0[/code] not affecting sky rendering at all.
+			[b]Note:[/b] [member volumetric_fog_sky_affect] also affects [FogVolume]s, even if [member volumetric_fog_density] is [code]0.0[/code]. If you notice [FogVolume]s are disappearing when looking towards the sky, set [member volumetric_fog_sky_affect] to [code]1.0[/code].
 		</member>
 		<member name="volumetric_fog_temporal_reprojection_amount" type="float" setter="set_volumetric_fog_temporal_reprojection_amount" getter="get_volumetric_fog_temporal_reprojection_amount" default="0.9">
 			The amount by which to blend the last frame with the current frame. A higher number results in smoother volumetric fog, but makes "ghosting" much worse. A lower value reduces ghosting but can result in the per-frame temporal jitter becoming visible.
 		</member>
 		<member name="volumetric_fog_temporal_reprojection_enabled" type="bool" setter="set_volumetric_fog_temporal_reprojection_enabled" getter="is_volumetric_fog_temporal_reprojection_enabled" default="true">
-			Enables temporal reprojection in the volumetric fog. Temporal reprojection blends the current frame's volumetric fog with the last frame's volumetric fog to smooth out jagged edges. The performance cost is minimal, however it does lead to moving [FogVolume]s and [Light3D]s "ghosting" and leaving a trail behind them. When temporal reprojection is enabled, try to avoid moving [FogVolume]s or [Light3D]s too fast.
+			Enables temporal reprojection in the volumetric fog. Temporal reprojection blends the current frame's volumetric fog with the last frame's volumetric fog to smooth out jagged edges. The performance cost is minimal; however, it leads to moving [FogVolume]s and [Light3D]s "ghosting" and leaving a trail behind them. When temporal reprojection is enabled, try to avoid moving [FogVolume]s or [Light3D]s too fast. Short-lived dynamic lighting effects should have [member Light3D.light_volumetric_fog_energy] set to [code]0.0[/code] to avoid ghosting.
 		</member>
 	</members>
 	<constants>

doc/classes/FogMaterial.xml

@@ -5,27 +5,28 @@
 	</brief_description>
 	<description>
 		A [Material] resource that can be used by [FogVolume]s to draw volumetric effects.
+		If you need more advanced effects, use a custom [url=$DOCS_URL/tutorials/shaders/shader_reference/fog_shader.html]fog shader[/url].
 	</description>
 	<tutorials>
 	</tutorials>
 	<members>
 		<member name="albedo" type="Color" setter="set_albedo" getter="get_albedo" default="Color(1, 1, 1, 1)">
-			Sets the single-scattering [Color] of the [FogVolume]. Internally [member albedo] is converted into single-scattering which is additively blended with other [FogVolume]s and the [member Environment.volumetric_fog_albedo].
+			The single-scattering [Color] of the [FogVolume]. Internally, [member albedo] is converted into single-scattering, which is additively blended with other [FogVolume]s and the [member Environment.volumetric_fog_albedo].
 		</member>
 		<member name="density" type="float" setter="set_density" getter="get_density" default="1.0">
-			Sets the density of the [FogVolume]. Denser objects are more opaque, but may suffer from under-sampling artifacts that look like stripes.
+			The density of the [FogVolume]. Denser objects are more opaque, but may suffer from under-sampling artifacts that look like stripes. Negative values can be used to subtract fog from other [FogVolume]s or global volumetric fog.
 		</member>
 		<member name="density_texture" type="Texture3D" setter="set_density_texture" getter="get_density_texture">
-			Sets a 3D texture that is used to scale the [member density] of the [FogVolume].
+			The 3D texture that is used to scale the [member density] of the [FogVolume]. This can be used to vary fog density within the [FogVolume] with any kind of static pattern. For animated effects, consider using a custom [url=$DOCS_URL/tutorials/shaders/shader_reference/fog_shader.html]fog shader[/url].
 		</member>
 		<member name="edge_fade" type="float" setter="set_edge_fade" getter="get_edge_fade" default="0.1">
-			Sets the hardness of the edges of the [FogVolume]. A higher number will result in softer edges while a lower number will result in harder edges.
+			The hardness of the edges of the [FogVolume]. A higher value will result in softer edges, while a lower value will result in harder edges.
 		</member>
 		<member name="emission" type="Color" setter="set_emission" getter="get_emission" default="Color(0, 0, 0, 1)">
-			Sets the [Color] of the light emitted by the [FogVolume]. Emitted light will not cast light or shadows on other objects, but can be useful for modulating the [Color] of the [FogVolume] independently from light sources.
+			The [Color] of the light emitted by the [FogVolume]. Emitted light will not cast light or shadows on other objects, but can be useful for modulating the [Color] of the [FogVolume] independently from light sources.
 		</member>
 		<member name="height_falloff" type="float" setter="set_height_falloff" getter="get_height_falloff" default="0.0">
-			Sets the rate by which the height-based fog decreases in density as height increases in world space. A high falloff will result in a sharp transition, while a low falloff will result in a smoother transition. A value of [code]0[/code] results in uniform-density fog. The height threshold is determined by the height of the associated [FogVolume].
+			The rate by which the height-based fog decreases in density as height increases in world space. A high falloff will result in a sharp transition, while a low falloff will result in a smoother transition. A value of [code]0.0[/code] results in uniform-density fog. The height threshold is determined by the height of the associated [FogVolume].
 		</member>
 	</members>
 </class>

doc/classes/FogVolume.xml

@@ -4,22 +4,23 @@
 		A node used to add local fog with the volumetric fog effect.
 	</brief_description>
 	<description>
-		[FogVolume]s are used to add localized fog into the global volumetric fog effect.
+		[FogVolume]s are used to add localized fog into the global volumetric fog effect. [FogVolume]s can also remove volumetric fog from specific areas if using a [FogMaterial] with a negative [member FogMaterial.density].
 		Performance of [FogVolume]s is directly related to their relative size on the screen and the complexity of their attached [FogMaterial]. It is best to keep [FogVolume]s relatively small and simple where possible.
+		[b]Note:[/b] [FogVolume]s only have a visible effect if [member Environment.volumetric_fog_enabled] is [code]true[/code]. If you don't want fog to be globally visible (but only within [FogVolume] nodes), set [member Environment.volumetric_fog_density] to [code]0.0[/code].
 	</description>
 	<tutorials>
 	</tutorials>
 	<members>
 		<member name="extents" type="Vector3" setter="set_extents" getter="get_extents" default="Vector3(1, 1, 1)">
-			Sets the size of the [FogVolume] when [member shape] is [constant RenderingServer.FOG_VOLUME_SHAPE_ELLIPSOID], [constant RenderingServer.FOG_VOLUME_SHAPE_CONE], [constant RenderingServer.FOG_VOLUME_SHAPE_CYLINDER] or [constant RenderingServer.FOG_VOLUME_SHAPE_BOX].
+			The size of the [FogVolume] when [member shape] is [constant RenderingServer.FOG_VOLUME_SHAPE_ELLIPSOID], [constant RenderingServer.FOG_VOLUME_SHAPE_CONE], [constant RenderingServer.FOG_VOLUME_SHAPE_CYLINDER] or [constant RenderingServer.FOG_VOLUME_SHAPE_BOX].
 			[b]Note:[/b] Thin fog volumes may appear to flicker when the camera moves or rotates. This can be alleviated by increasing [member ProjectSettings.rendering/environment/volumetric_fog/volume_depth] (at a performance cost) or by decreasing [member Environment.volumetric_fog_length] (at no performance cost, but at the cost of lower fog range). Alternatively, the [FogVolume] can be made thicker and use a lower density in the [member material].
 			[b]Note:[/b] If [member shape] is [constant RenderingServer.FOG_VOLUME_SHAPE_CONE] or [constant RenderingServer.FOG_VOLUME_SHAPE_CYLINDER], the cone/cylinder will be adjusted to fit within the extents. Non-uniform scaling of cone/cylinder shapes via the [member extents] property is not supported, but you can scale the [FogVolume] node instead.
 		</member>
 		<member name="material" type="Material" setter="set_material" getter="get_material">
-			Sets the [Material] to be used by the [FogVolume]. Can be either a [FogMaterial] or a custom [ShaderMaterial].
+			The [Material] used by the [FogVolume]. Can be either a built-in [FogMaterial] or a custom [ShaderMaterial].
 		</member>
 		<member name="shape" type="int" setter="set_shape" getter="get_shape" enum="RenderingServer.FogVolumeShape" default="3">
-			Sets the shape of the [FogVolume] to either [constant RenderingServer.FOG_VOLUME_SHAPE_ELLIPSOID], [constant RenderingServer.FOG_VOLUME_SHAPE_CONE], [constant RenderingServer.FOG_VOLUME_SHAPE_CYLINDER], [constant RenderingServer.FOG_VOLUME_SHAPE_BOX] or [constant RenderingServer.FOG_VOLUME_SHAPE_WORLD].
+			The shape of the [FogVolume]. This can be set to either [constant RenderingServer.FOG_VOLUME_SHAPE_ELLIPSOID], [constant RenderingServer.FOG_VOLUME_SHAPE_CONE], [constant RenderingServer.FOG_VOLUME_SHAPE_CYLINDER], [constant RenderingServer.FOG_VOLUME_SHAPE_BOX] or [constant RenderingServer.FOG_VOLUME_SHAPE_WORLD].
 		</member>
 	</members>
 </class>

doc/classes/ProjectSettings.xml

@@ -1776,7 +1776,7 @@
 			Enables filtering of the volumetric fog effect prior to integration. This substantially blurs the fog which reduces fine details but also smooths out harsh edges and aliasing artifacts. Disable when more detail is required.
 		</member>
 		<member name="rendering/environment/volumetric_fog/volume_depth" type="int" setter="" getter="" default="64">
-			Number of slices to use along the depth of the froxel buffer for volumetric fog. A lower number will be more efficient but may result in artifacts appearing during camera movement.
+			Number of slices to use along the depth of the froxel buffer for volumetric fog. A lower number will be more efficient but may result in artifacts appearing during camera movement. See also [member Environment.volumetric_fog_length].
 		</member>
 		<member name="rendering/environment/volumetric_fog/volume_size" type="int" setter="" getter="" default="64">
 			Base size used to determine size of froxel buffer in the camera X-axis and Y-axis. The final size is scaled by the aspect ratio of the screen, so actual values may differ from what is set. Set a larger size for more detailed fog, set a smaller size for better performance.