This commits adds a new emitter type for particles material

and 3D CPU particles. The new emitter is called "ring"
and it can emit either in a ring or cylinder fashion.
This adds the following properties for the emitter:
1. emission_ring_axis: the axis along which the ring/cylinder
    will be constructed
2. emission_ring_radius: outer radius of the ring/cylinder
3. emission_ring_inner_radius: inner radius of the cylinder.
    when set to zero, particles will emit in the full volume.
4. emission_ring_height: height of the ring/cylinder emitter.

2 files changed, 33 insertions, 3 deletions

diff --git a/doc/classes/CPUParticles3D.xml b/doc/classes/CPUParticles3D.xml
index 7509775d20..3c479f9652 100644
--- a/doc/classes/CPUParticles3D.xml
+++ b/doc/classes/CPUParticles3D.xml
@@ -177,9 +177,21 @@
 		<member name="emission_normals" type="PackedVector3Array" setter="set_emission_normals" getter="get_emission_normals">
 			Sets the direction the particles will be emitted in when using [constant EMISSION_SHAPE_DIRECTED_POINTS].
 		</member>
-		<member name="emission_points" type="PackedVector3Array" setter="set_emission_points" getter="get_emission_points" default="PackedVector3Array()">
+		<member name="emission_points" type="PackedVector3Array" setter="set_emission_points" getter="get_emission_points">
 			Sets the initial positions to spawn particles when using [constant EMISSION_SHAPE_POINTS] or [constant EMISSION_SHAPE_DIRECTED_POINTS].
 		</member>
+		<member name="emission_ring_axis" type="Vector3" setter="set_emission_ring_axis" getter="get_emission_ring_axis">
+			The axis of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
+		<member name="emission_ring_height" type="float" setter="set_emission_ring_height" getter="get_emission_ring_height">
+			The height of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
+		<member name="emission_ring_inner_radius" type="float" setter="set_emission_ring_inner_radius" getter="get_emission_ring_inner_radius">
+			The inner radius of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
+		<member name="emission_ring_radius" type="float" setter="set_emission_ring_radius" getter="get_emission_ring_radius">
+			The radius of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
 		<member name="emission_shape" type="int" setter="set_emission_shape" getter="get_emission_shape" enum="CPUParticles3D.EmissionShape" default="0">
 			Particles will be emitted inside this region. See [enum EmissionShape] for possible values.
 		</member>
@@ -378,7 +390,10 @@
 		<constant name="EMISSION_SHAPE_DIRECTED_POINTS" value="4" enum="EmissionShape">
 			Particles will be emitted at a position chosen randomly among [member emission_points]. Particle velocity and rotation will be set based on [member emission_normals]. Particle color will be modulated by [member emission_colors].
 		</constant>
-		<constant name="EMISSION_SHAPE_MAX" value="5" enum="EmissionShape">
+		<constant name="EMISSION_SHAPE_RING" value="5" enum="EmissionShape">
+			Particles will be emitted in a ring or cylinder.
+		</constant>
+		<constant name="EMISSION_SHAPE_MAX" value="6" enum="EmissionShape">
 			Represents the size of the [enum EmissionShape] enum.
 		</constant>
 	</constants>
diff --git a/doc/classes/ParticlesMaterial.xml b/doc/classes/ParticlesMaterial.xml
index e8fde21032..c613369bbc 100644
--- a/doc/classes/ParticlesMaterial.xml
+++ b/doc/classes/ParticlesMaterial.xml
@@ -174,6 +174,18 @@
 		<member name="emission_point_texture" type="Texture2D" setter="set_emission_point_texture" getter="get_emission_point_texture">
 			Particles will be emitted at positions determined by sampling this texture at a random position. Used with [constant EMISSION_SHAPE_POINTS] and [constant EMISSION_SHAPE_DIRECTED_POINTS]. Can be created automatically from mesh or node by selecting "Create Emission Points from Mesh/Node" under the "Particles" tool in the toolbar.
 		</member>
+		<member name="emission_ring_axis" type="Vector3" setter="set_emission_ring_axis" getter="get_emission_ring_axis">
+			The axis of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
+		<member name="emission_ring_height" type="float" setter="set_emission_ring_height" getter="get_emission_ring_height">
+			The height of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
+		<member name="emission_ring_inner_radius" type="float" setter="set_emission_ring_inner_radius" getter="get_emission_ring_inner_radius">
+			The inner radius of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
+		<member name="emission_ring_radius" type="float" setter="set_emission_ring_radius" getter="get_emission_ring_radius">
+			The radius of the ring when using the emitter [constant EMISSION_SHAPE_RING].
+		</member>
 		<member name="emission_shape" type="int" setter="set_emission_shape" getter="get_emission_shape" enum="ParticlesMaterial.EmissionShape" default="0">
 			Particles will be emitted inside this region. Use [enum EmissionShape] constants for values.
 		</member>
@@ -338,7 +350,10 @@
 		<constant name="EMISSION_SHAPE_DIRECTED_POINTS" value="4" enum="EmissionShape">
 			Particles will be emitted at a position determined by sampling a random point on the [member emission_point_texture]. Particle velocity and rotation will be set based on [member emission_normal_texture]. Particle color will be modulated by [member emission_color_texture].
 		</constant>
-		<constant name="EMISSION_SHAPE_MAX" value="5" enum="EmissionShape">
+		<constant name="EMISSION_SHAPE_RING" value="5" enum="EmissionShape">
+			Particles will be emitted in a ring or cylinder.
+		</constant>
+		<constant name="EMISSION_SHAPE_MAX" value="6" enum="EmissionShape">
 			Represents the size of the [enum EmissionShape] enum.
 		</constant>
 		<constant name="SUB_EMITTER_DISABLED" value="0" enum="SubEmitterMode">