Add a shadow opacity property to Light3D

This can be used to make shadows translucent for a specific light.

The light distance fade system also uses this to smoothly fade the shadow
when the light fade transition distance is greater than 0.

2 files changed, 20 insertions, 10 deletions

diff --git a/doc/classes/Light3D.xml b/doc/classes/Light3D.xml
index 0ebd83c882..46c3e57547 100644
--- a/doc/classes/Light3D.xml
+++ b/doc/classes/Light3D.xml
@@ -37,13 +37,12 @@
 			[b]Note:[/b] Only effective for [OmniLight3D] and [SpotLight3D].
 		</member>
 		<member name="distance_fade_length" type="float" setter="set_distance_fade_length" getter="get_distance_fade_length" default="10.0">
-			Distance over which the light fades. The light's energy is progressively reduced over this distance and is completely invisible at the end.
+			Distance over which the light and its shadow fades. The light's energy and shadow's opacity is progressively reduced over this distance and is completely invisible at the end.
 			[b]Note:[/b] Only effective for [OmniLight3D] and [SpotLight3D].
 		</member>
 		<member name="distance_fade_shadow" type="float" setter="set_distance_fade_shadow" getter="get_distance_fade_shadow" default="50.0">
 			The distance from the camera at which the light's shadow cuts off (in 3D units). Set this to a value lower than [member distance_fade_begin] + [member distance_fade_length] to further improve performance, as shadow rendering is often more expensive than light rendering itself.
 			[b]Note:[/b] Only effective for [OmniLight3D] and [SpotLight3D], and only when [member shadow_enabled] is [code]true[/code].
-			[b]Note:[/b] Due to a rendering engine limitation, shadows will be disabled instantly instead of fading smoothly according to [member distance_fade_length]. This may result in visible pop-in depending on the scene topography.
 		</member>
 		<member name="editor_only" type="bool" setter="set_editor_only" getter="is_editor_only" default="false">
 			If [code]true[/code], the light only appears in the editor and will not be visible at runtime.
@@ -95,6 +94,9 @@
 		<member name="shadow_normal_bias" type="float" setter="set_param" getter="get_param" default="1.0">
 			Offsets the lookup into the shadow map by the object's normal. This can be used to reduce self-shadowing artifacts without using [member shadow_bias]. In practice, this value should be tweaked along with [member shadow_bias] to reduce artifacts as much as possible.
 		</member>
+		<member name="shadow_opacity" type="float" setter="set_param" getter="get_param" default="1.0">
+			The opacity to use when rendering the light's shadow map. Values lower than [code]1.0[/code] make the light appear through shadows. This can be used to fake global illumination at a low performance cost.
+		</member>
 		<member name="shadow_reverse_cull_face" type="bool" setter="set_shadow_reverse_cull_face" getter="get_shadow_reverse_cull_face" default="false">
 			If [code]true[/code], reverses the backface culling of the mesh. This can be useful when you have a flat mesh that has a light behind it. If you need to cast a shadow on both sides of the mesh, set the mesh to use double-sided shadows with [constant GeometryInstance3D.SHADOW_CASTING_SETTING_DOUBLE_SIDED].
 		</member>
@@ -150,15 +152,19 @@
 		<constant name="PARAM_SHADOW_PANCAKE_SIZE" value="15" enum="Param">
 			Constant for accessing [member DirectionalLight3D.directional_shadow_pancake_size].
 		</constant>
-		<constant name="PARAM_SHADOW_BLUR" value="16" enum="Param">
+		<constant name="PARAM_SHADOW_OPACITY" value="16" enum="Param">
+			Constant for accessing [member shadow_opacity].
+		</constant>
+		<constant name="PARAM_SHADOW_BLUR" value="17" enum="Param">
 			Constant for accessing [member shadow_blur].
 		</constant>
-		<constant name="PARAM_SHADOW_VOLUMETRIC_FOG_FADE" value="17" enum="Param">
+		<constant name="PARAM_SHADOW_VOLUMETRIC_FOG_FADE" value="18" enum="Param">
+			Constant for accessing [member shadow_fog_fade].
 		</constant>
-		<constant name="PARAM_TRANSMITTANCE_BIAS" value="18" enum="Param">
+		<constant name="PARAM_TRANSMITTANCE_BIAS" value="19" enum="Param">
 			Constant for accessing [member shadow_transmittance_bias].
 		</constant>
-		<constant name="PARAM_MAX" value="19" enum="Param">
+		<constant name="PARAM_MAX" value="20" enum="Param">
 			Represents the size of the [enum Param] enum.
 		</constant>
 		<constant name="BAKE_DISABLED" value="0" enum="BakeMode">
diff --git a/doc/classes/RenderingServer.xml b/doc/classes/RenderingServer.xml
index 1b58b50bc7..c06b2e1d98 100644
--- a/doc/classes/RenderingServer.xml
+++ b/doc/classes/RenderingServer.xml
@@ -3777,6 +3777,7 @@
 			The light's energy.
 		</constant>
 		<constant name="LIGHT_PARAM_INDIRECT_ENERGY" value="1" enum="LightParam">
+			The light's indirect energy multiplier (final indirect energy is [constant LIGHT_PARAM_ENERGY] * [constant LIGHT_PARAM_INDIRECT_ENERGY]).
 		</constant>
 		<constant name="LIGHT_PARAM_SPECULAR" value="2" enum="LightParam">
 			The light's influence on specularity.
@@ -3820,14 +3821,17 @@
 		<constant name="LIGHT_PARAM_SHADOW_PANCAKE_SIZE" value="15" enum="LightParam">
 			Sets the size of the directional shadow pancake. The pancake offsets the start of the shadow's camera frustum to provide a higher effective depth resolution for the shadow. However, a high pancake size can cause artifacts in the shadows of large objects that are close to the edge of the frustum. Reducing the pancake size can help. Setting the size to [code]0[/code] turns off the pancaking effect.
 		</constant>
-		<constant name="LIGHT_PARAM_SHADOW_BLUR" value="16" enum="LightParam">
+		<constant name="LIGHT_PARAM_SHADOW_OPACITY" value="16" enum="LightParam">
+			The light's shadow opacity. Values lower than [code]1.0[/code] make the light appear through shadows. This can be used to fake global illumination at a low performance cost.
+		</constant>
+		<constant name="LIGHT_PARAM_SHADOW_BLUR" value="17" enum="LightParam">
 			Blurs the edges of the shadow. Can be used to hide pixel artifacts in low resolution shadow maps. A high value can make shadows appear grainy and can cause other unwanted artifacts. Try to keep as near default as possible.
 		</constant>
-		<constant name="LIGHT_PARAM_SHADOW_VOLUMETRIC_FOG_FADE" value="17" enum="LightParam">
+		<constant name="LIGHT_PARAM_SHADOW_VOLUMETRIC_FOG_FADE" value="18" enum="LightParam">
 		</constant>
-		<constant name="LIGHT_PARAM_TRANSMITTANCE_BIAS" value="18" enum="LightParam">
+		<constant name="LIGHT_PARAM_TRANSMITTANCE_BIAS" value="19" enum="LightParam">
 		</constant>
-		<constant name="LIGHT_PARAM_MAX" value="19" enum="LightParam">
+		<constant name="LIGHT_PARAM_MAX" value="20" enum="LightParam">
 			Represents the size of the [enum LightParam] enum.
 		</constant>
 		<constant name="LIGHT_BAKE_DISABLED" value="0" enum="LightBakeMode">