Add "Hide on Contact" collision mode to ParticlesMaterial

This can be used to make particles disappear when colliding, rather
than bouncing around or sticking to surfaces.

This is useful for rain particles which should not be able to go
through floors/ceilings, but shouldn't stick to surfaces either.

6 files changed, 25 insertions, 12 deletions

diff --git a/doc/classes/GPUParticlesCollision3D.xml b/doc/classes/GPUParticlesCollision3D.xml
index 435f9781f0..27e3590e75 100644
--- a/doc/classes/GPUParticlesCollision3D.xml
+++ b/doc/classes/GPUParticlesCollision3D.xml
@@ -7,7 +7,7 @@
 		Particle collision shapes can be used to make particles stop or bounce against them.
 		Particle collision shapes in real-time and can be moved, rotated and scaled during gameplay. Unlike attractors, non-uniform scaling of collision shapes is [i]not[/i] supported.
 		Particle collision shapes can be temporarily disabled by hiding them.
-		[b]Note:[/b] [member ParticlesMaterial.collision_enabled] must be [code]true[/code] on the [GPUParticles3D]'s process material for collision to work.
+		[b]Note:[/b] [member ParticlesMaterial.collision_mode] must be [constant ParticlesMaterial.COLLISION_RIGID] or [constant ParticlesMaterial.COLLISION_HIDE_ON_CONTACT] on the [GPUParticles3D]'s process material for collision to work.
 		[b]Note:[/b] Particle collision only affects [GPUParticles3D], not [CPUParticles3D].
 		[b]Note:[/b] Particles pushed by a collider that is being moved will not be interpolated, which can result in visible stuttering. This can be alleviated by setting [member GPUParticles3D.fixed_fps] to [code]0[/code] or a value that matches or exceeds the target framerate.
 	</description>
@@ -15,7 +15,7 @@
 	</tutorials>
 	<members>
 		<member name="cull_mask" type="int" setter="set_cull_mask" getter="get_cull_mask" default="4294967295">
-			The particle rendering layers ([member VisualInstance3D.layers]) that will be affected by the collision shape. By default, all particles that have [member ParticlesMaterial.collision_enabled] set to [code]true[/code] will be affected by a collision shape.
+			The particle rendering layers ([member VisualInstance3D.layers]) that will be affected by the collision shape. By default, all particles that have [member ParticlesMaterial.collision_mode] set to [constant ParticlesMaterial.COLLISION_RIGID] or [constant ParticlesMaterial.COLLISION_HIDE_ON_CONTACT] will be affected by a collision shape.
 			After configuring particle nodes accordingly, specific layers can be unchecked to prevent certain particles from being affected by attractors. For example, this can be used if you're using an attractor as part of a spell effect but don't want the attractor to affect unrelated weather particles at the same position.
 			Particle attraction can also be disabled on a per-process material basis by setting [member ParticlesMaterial.attractor_interaction_enabled] on the [GPUParticles3D] node.
 		</member>
diff --git a/doc/classes/GPUParticlesCollisionBox3D.xml b/doc/classes/GPUParticlesCollisionBox3D.xml
index 60d66ca682..65b69c0098 100644
--- a/doc/classes/GPUParticlesCollisionBox3D.xml
+++ b/doc/classes/GPUParticlesCollisionBox3D.xml
@@ -5,7 +5,7 @@
 	</brief_description>
 	<description>
 		Box-shaped 3D particle collision shape affecting [GPUParticles3D] nodes.
-		[b]Note:[/b] [member ParticlesMaterial.collision_enabled] must be [code]true[/code] on the [GPUParticles3D]'s process material for collision to work.
+		[b]Note:[/b] [member ParticlesMaterial.collision_mode] must be [constant ParticlesMaterial.COLLISION_RIGID] or [constant ParticlesMaterial.COLLISION_HIDE_ON_CONTACT] on the [GPUParticles3D]'s process material for collision to work.
 		[b]Note:[/b] Particle collision only affects [GPUParticles3D], not [CPUParticles3D].
 	</description>
 	<tutorials>
diff --git a/doc/classes/GPUParticlesCollisionHeightField3D.xml b/doc/classes/GPUParticlesCollisionHeightField3D.xml
index 3fcad43efb..72d273112e 100644
--- a/doc/classes/GPUParticlesCollisionHeightField3D.xml
+++ b/doc/classes/GPUParticlesCollisionHeightField3D.xml
@@ -7,7 +7,7 @@
 		Real-time heightmap-shaped 3D particle attractor affecting [GPUParticles3D] nodes.
 		Heightmap shapes allow for efficiently representing collisions for convex and concave objects with a single "floor" (such as terrain). This is less flexible than [GPUParticlesCollisionSDF3D], but it doesn't require a baking step.
 		[GPUParticlesCollisionHeightField3D] can also be regenerated in real-time when it is moved, when the camera moves, or even continuously. This makes [GPUParticlesCollisionHeightField3D] a good choice for weather effects such as rain and snow and games with highly dynamic geometry. However, since heightmaps cannot represent overhangs, [GPUParticlesCollisionHeightField3D] is not suited for indoor particle collision.
-		[b]Note:[/b] [member ParticlesMaterial.collision_enabled] must be [code]true[/code] on the [GPUParticles3D]'s process material for collision to work.
+		[b]Note:[/b] [member ParticlesMaterial.collision_mode] must be [constant ParticlesMaterial.COLLISION_RIGID] or [constant ParticlesMaterial.COLLISION_HIDE_ON_CONTACT] on the [GPUParticles3D]'s process material for collision to work.
 		[b]Note:[/b] Particle collision only affects [GPUParticles3D], not [CPUParticles3D].
 	</description>
 	<tutorials>
diff --git a/doc/classes/GPUParticlesCollisionSDF3D.xml b/doc/classes/GPUParticlesCollisionSDF3D.xml
index 29adf4fbc1..0e7640ba89 100644
--- a/doc/classes/GPUParticlesCollisionSDF3D.xml
+++ b/doc/classes/GPUParticlesCollisionSDF3D.xml
@@ -8,7 +8,7 @@
 		Signed distance fields (SDF) allow for efficiently representing approximate collision shapes for convex and concave objects of any shape. This is more flexible than [GPUParticlesCollisionHeightField3D], but it requires a baking step.
 		[b]Baking:[/b] The signed distance field texture can be baked by selecting the [GPUParticlesCollisionSDF3D] node in the editor, then clicking [b]Bake SDF[/b] at the top of the 3D viewport. Any [i]visible[/i] [MeshInstance3D]s touching the [member extents] will be taken into account for baking, regardless of their [member GeometryInstance3D.gi_mode].
 		[b]Note:[/b] Baking a [GPUParticlesCollisionSDF3D]'s [member texture] is only possible within the editor, as there is no bake method exposed for use in exported projects. However, it's still possible to load pre-baked [Texture3D]s into its [member texture] property in an exported project.
-		[b]Note:[/b] [member ParticlesMaterial.collision_enabled] must be [code]true[/code] on the [GPUParticles3D]'s process material for collision to work.
+		[b]Note:[/b] [member ParticlesMaterial.collision_mode] must be [constant ParticlesMaterial.COLLISION_RIGID] or [constant ParticlesMaterial.COLLISION_HIDE_ON_CONTACT] on the [GPUParticles3D]'s process material for collision to work.
 		[b]Note:[/b] Particle collision only affects [GPUParticles3D], not [CPUParticles3D].
 	</description>
 	<tutorials>
diff --git a/doc/classes/GPUParticlesCollisionSphere3D.xml b/doc/classes/GPUParticlesCollisionSphere3D.xml
index 6651a732da..bfebe05005 100644
--- a/doc/classes/GPUParticlesCollisionSphere3D.xml
+++ b/doc/classes/GPUParticlesCollisionSphere3D.xml
@@ -5,7 +5,7 @@
 	</brief_description>
 	<description>
 		Sphere-shaped 3D particle collision shape affecting [GPUParticles3D] nodes.
-		[b]Note:[/b] [member ParticlesMaterial.collision_enabled] must be [code]true[/code] on the [GPUParticles3D]'s process material for collision to work.
+		[b]Note:[/b] [member ParticlesMaterial.collision_mode] must be [constant ParticlesMaterial.COLLISION_RIGID] or [constant ParticlesMaterial.COLLISION_HIDE_ON_CONTACT] on the [GPUParticles3D]'s process material for collision to work.
 		[b]Note:[/b] Particle collision only affects [GPUParticles3D], not [CPUParticles3D].
 	</description>
 	<tutorials>
diff --git a/doc/classes/ParticlesMaterial.xml b/doc/classes/ParticlesMaterial.xml
index fe4caaa10c..55f4c4dcdd 100644
--- a/doc/classes/ParticlesMaterial.xml
+++ b/doc/classes/ParticlesMaterial.xml
@@ -115,14 +115,15 @@
 		<member name="attractor_interaction_enabled" type="bool" setter="set_attractor_interaction_enabled" getter="is_attractor_interaction_enabled" default="true">
 			True if the interaction with particle attractors is enabled.
 		</member>
-		<member name="collision_bounce" type="float" setter="set_collision_bounce" getter="get_collision_bounce" default="0.0">
-			Collision bounciness.
+		<member name="collision_bounce" type="float" setter="set_collision_bounce" getter="get_collision_bounce">
+			The particles' bounciness. Values range from [code]0[/code] (no bounce) to [code]1[/code] (full bounciness). Only effective if [member collision_mode] is [constant COLLISION_RIGID].
 		</member>
-		<member name="collision_enabled" type="bool" setter="set_collision_enabled" getter="is_collision_enabled" default="false">
-			True if collisions are enabled for this particle system.
+		<member name="collision_friction" type="float" setter="set_collision_friction" getter="get_collision_friction">
+			The particles' friction. Values range from [code]0[/code] (frictionless) to [code]1[/code] (maximum friction). Only effective if [member collision_mode] is [constant COLLISION_RIGID].
 		</member>
-		<member name="collision_friction" type="float" setter="set_collision_friction" getter="get_collision_friction" default="0.0">
-			Collision friction.
+		<member name="collision_mode" type="int" setter="set_collision_mode" getter="get_collision_mode" enum="ParticlesMaterial.CollisionMode" default="0">
+			The particles' collision mode.
+			[b]Note:[/b] Particles can only collide with [GPUParticlesCollision3D] nodes, not [PhysicsBody3D] nodes. To make particles collide with various objects, you can add [GPUParticlesCollision3D] nodes as children of [PhysicsBody3D] nodes.
 		</member>
 		<member name="collision_use_scale" type="bool" setter="set_collision_use_scale" getter="is_collision_using_scale" default="false">
 			Should collision take scale into account.
@@ -404,5 +405,17 @@
 		<constant name="SUB_EMITTER_MAX" value="4" enum="SubEmitterMode">
 			Represents the size of the [enum SubEmitterMode] enum.
 		</constant>
+		<constant name="COLLISION_DISABLED" value="0" enum="CollisionMode">
+			No collision for particles. Particles will go through [GPUParticlesCollision3D] nodes.
+		</constant>
+		<constant name="COLLISION_RIGID" value="1" enum="CollisionMode">
+			[RigidDynamicBody3D]-style collision for particles using [GPUParticlesCollision3D] nodes.
+		</constant>
+		<constant name="COLLISION_HIDE_ON_CONTACT" value="2" enum="CollisionMode">
+			Hide particles instantly when colliding with a [GPUParticlesCollision3D] node. This can be combined with a subemitter that uses the [constant COLLISION_RIGID] collision mode to "replace" the parent particle with the subemitter on impact.
+		</constant>
+		<constant name="COLLISION_MAX" value="3" enum="CollisionMode">
+			Represents the size of the [enum CollisionMode] enum.
+		</constant>
 	</constants>
 </class>