Grass shell Texturing

Demo shell texturing for grass using shader and MultiMeshInstance.

camera.gd

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+extends Node3D
+class_name RotateCamera
+
+@export var camera_rotate_sensitivity: float = 0.005
+@export var camera_zoom_sensititivy: float = 0.01
+@export var zoom_max: float = 10.
+@export var zoom_min: float = 0.1
+
+@onready var camera: Camera3D = $Camera3D
+
+var camera_rotate_diff: Vector3 = Vector3()
+var camera_zoom_weight: float = .15
+
+var enable_rotate: bool = false
+
+func _process(delta):
+	self._update_rotation()
+	self._update_zoom()
+
+func _unhandled_input(event):
+	if self.enable_rotate and event is InputEventMouseMotion:
+		self.camera_rotate_diff.y -= event.relative.x
+		self.camera_rotate_diff.x -= event.relative.y
+	elif event is InputEventMouseButton:
+		if event.is_action_pressed("camera_rotate_button"):
+			self.enable_rotate = true
+		elif event.is_action_released("camera_rotate_button"):
+			self.enable_rotate = false
+		elif event.is_action_pressed("camera_zoom_in"):
+			self.camera_zoom_weight = clampf(self.camera_zoom_weight - camera_zoom_sensititivy, 0., 1.)
+		elif event.is_action_pressed("camera_zoom_out"):
+			self.camera_zoom_weight = clampf(self.camera_zoom_weight + camera_zoom_sensititivy, 0., 1.)
+			
+
+func _update_rotation():
+	if self.enable_rotate:
+		self.rotation += self.camera_rotate_diff * camera_rotate_sensitivity
+	self.camera_rotate_diff = Vector3.ZERO
+
+func _update_zoom():
+	var from = self.global_position
+	var to = self.global_position + self.camera.get_global_transform().basis.z * zoom_max
+	
+	var new_cam_pos = lerp(from, to, camera_zoom_weight)
+	self.camera.global_position = new_cam_pos
+	

camera.tscn

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+[gd_scene load_steps=2 format=3 uid="uid://bkavbjcx1vhaf"]
+
+[ext_resource type="Script" path="res://camera.gd" id="1_bmlh2"]
+
+[node name="camera_root" type="Node3D"]
+transform = Transform3D(1, 0, 0, 0, 0.869029, 0.494761, 0, -0.494761, 0.869029, 0, 0, 0)
+script = ExtResource("1_bmlh2")
+
+[node name="Camera3D" type="Camera3D" parent="."]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0.306079, 2.53232)

grass.gdshader

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+shader_type spatial;
+render_mode cull_disabled;
+
+//uniform int _ShellIndex;  // index of shell being worked on (0 -> _ShellCount)
+uniform float _NoiseMin;  // minimum strand length
+uniform float _NoiseMax;  // maxmimum strand length
+uniform float _ShellLength;  // amount of distance that the shells cover, 1 means shells will span across 1 world space unit
+uniform int _ShellCount;  // total number of shells (for normalizing the shell index)
+uniform float _ShellDistanceAttenuation;  // exponent how far to push the shell outwards
+uniform float _Thickness;  // how thick a strand shall be
+uniform float _Attenuation;  // AO strength factor
+uniform float _OcclusionBias;  // additive bias for AO
+uniform vec3 _ShellColor;
+
+uniform float _Density; // amout of strands to generate
+
+varying flat int _ShellIndex;
+
+float hash(uint n) {
+	n = (n << 13U) ^ n;
+	n = n * (n * n * 15731U + 1239221U) + 123376312589U;
+	return float(n & uint(0x7fffffffU)) / float(0x7fffffff);
+}
+
+void vertex() {
+	_ShellIndex = int(INSTANCE_CUSTOM.x);
+	float shell_height = float(_ShellIndex) / float(_ShellCount);
+	shell_height = pow(shell_height, _ShellDistanceAttenuation);
+	
+	VERTEX.xyz += NORMAL.xyz * _ShellLength * shell_height;
+	
+	//NORMAL = normalize(NORMAL);
+	UV = UV;
+}
+
+void fragment() {
+	vec2 newUV = UV * _Density;
+	vec2 localUV = fract(newUV) * 2. - 1.;
+	
+	float localDistanceFromCenter = length(localUV);
+	float h = float(_ShellIndex) / float(_ShellCount);  // normalized height
+	
+	uint seed = uint(int(newUV.x) + 100 * int(newUV.y) + 100 * 10);
+	
+	float rand = mix(_NoiseMin, _NoiseMax, hash(seed));  // getting random value for strand
+	
+	if (localDistanceFromCenter > _Thickness * (rand - h) && _ShellIndex > 0) discard;  // discarding pixels outside of thickness
+	
+	//float ndotl = dot(NORMAL, WORLD)  // TODO do light later?
+	float ambientOcclusion = pow(h, _Attenuation);  // fake Ambient Occlusion
+	ambientOcclusion += _OcclusionBias;
+	// Called for every pixel the material is visible on.
+	ALBEDO.rgb = _ShellColor * ambientOcclusion;
+	//ALPHA = 1.0;
+}
+
+void light() {
+	float ndotl = clamp(dot(NORMAL, LIGHT), 0., 1.) * .5 + .5;
+	
+	DIFFUSE_LIGHT += ndotl * ndotl;
+}

grass_plane_mesh.tres

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+[gd_resource type="QuadMesh" load_steps=3 format=3 uid="uid://obd7wi7g27sb"]
+
+[ext_resource type="Shader" path="res://grass.gdshader" id="1_5707v"]
+
+[sub_resource type="ShaderMaterial" id="ShaderMaterial_hgeuk"]
+render_priority = 0
+shader = ExtResource("1_5707v")
+shader_parameter/_NoiseMin = 0.4
+shader_parameter/_NoiseMax = 1.0
+shader_parameter/_ShellLength = 0.03
+shader_parameter/_ShellCount = 16
+shader_parameter/_ShellDistanceAttenuation = 1.0
+shader_parameter/_Thickness = 3.4
+shader_parameter/_Attenuation = null
+shader_parameter/_OcclusionBias = null
+shader_parameter/_ShellColor = Vector3(0.2, 0.7, 0.2)
+shader_parameter/_Density = 10.0
+
+[resource]
+material = SubResource("ShaderMaterial_hgeuk")
+subdivide_width = 32
+subdivide_depth = 32

icon.png.import

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+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://yafv1eyajxv0"
+path="res://.godot/imported/icon.png-487276ed1e3a0c39cad0279d744ee560.ctex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://icon.png"
+dest_files=["res://.godot/imported/icon.png-487276ed1e3a0c39cad0279d744ee560.ctex"]
+
+[params]
+
+compress/mode=0
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=false
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=1

main.tscn

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+[gd_scene load_steps=5 format=3 uid="uid://b45p5o8obc4rb"]
+
+[ext_resource type="PackedScene" uid="uid://bkavbjcx1vhaf" path="res://camera.tscn" id="1_fql2y"]
+[ext_resource type="PackedScene" uid="uid://gbmju3x1gp7y" path="res://multi_grass.tscn" id="3_lkk6e"]
+
+[sub_resource type="StandardMaterial3D" id="StandardMaterial3D_sivjy"]
+albedo_color = Color(0.2, 0.137255, 0.0431373, 1)
+
+[sub_resource type="PlaneMesh" id="PlaneMesh_vpqsi"]
+material = SubResource("StandardMaterial3D_sivjy")
+
+[node name="main" type="Node3D"]
+
+[node name="camera" parent="." instance=ExtResource("1_fql2y")]
+
+[node name="light" type="DirectionalLight3D" parent="."]
+transform = Transform3D(0.758372, 0.524229, 0.38737, -0.457532, 0.00484201, 0.88918, 0.464258, -0.851564, 0.243524, 1.21403, 2.38572, 0.933982)
+
+[node name="multi_grass" parent="." instance=ExtResource("3_lkk6e")]
+
+[node name="ground" type="MeshInstance3D" parent="."]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, -0.149795, 0)
+mesh = SubResource("PlaneMesh_vpqsi")

multi_grass.gd

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+extends MultiMeshInstance3D
+
+@export_range(1, 126) var shell_count = 64
+@export var noise_min: float = 0.4
+@export var noise_max: float = 1.0
+@export var shell_length: float = .1
+@export var shell_distance_attenuation: float = 1.
+@export var thickness: float = 3.4
+@export var attenuation: float = 1.98
+@export var occlusion_bias: float = .04
+@export var shell_color: Vector3 = Vector3(0.2, 0.7, 0.2)
+@export var density: int = 150
+
+func _generate_mmi(layers: int, mmi: MultiMeshInstance3D, mesh: Mesh, material: Material, cast_shadow: bool):
+	var mdt = MeshDataTool.new()
+	
+	if mmi.multimesh == null:
+		mmi.multimesh = MultiMesh.new()
+		mmi.multimesh.transform_format = MultiMesh.TRANSFORM_3D
+	
+	var new_mesh: Mesh = mesh.duplicate(true) as Mesh
+	#new_mesh = _normals_to_vertex_color(new_mesh, material)  # saves normal data as vertex color to be used by the shader (in the orig code)
+	mmi.multimesh.mesh = new_mesh
+	mmi.multimesh.instance_count = layers
+	mmi.multimesh.visible_instance_count = layers
+	for surface in new_mesh.get_surface_count():
+		material = ShaderMaterial.new()
+		material.set_shader(preload("res://grass.gdshader"))
+		mmi.multimesh.mesh.surface_set_material(surface, material.duplicate(true))
+	
+	for i in range(layers):
+		#mmi.multimesh.set_instance_transform(i, Transform3D(Basis(), Vector3(0., .1 * i, 0.)))
+		mmi.multimesh.set_instance_transform(i, Transform3D(Basis(), Vector3()))
+		var grey = float(i) / float(layers)
+		#mmi.multimesh.set_instance_color(i, Color(1., 1., 1., 1.))
+		
+		var mat = mmi.multimesh.mesh.surface_get_material(0)
+		if mat is ShaderMaterial:
+			#print("Setting shader params (", i, ")")
+			#mat.set_shader_parameter("_ShellIndex", i)
+			mmi.multimesh.set_instance_custom_data(i, Color(i, 0., 0., 0.))  # passes shell index for each instance
+			mat.set_shader_parameter("_NoiseMin", noise_min)
+			mat.set_shader_parameter("_NoiseMax", noise_max)
+			mat.set_shader_parameter("_ShellLength", shell_length)
+			mat.set_shader_parameter("_ShellCount", layers)
+			mat.set_shader_parameter("_ShellDistanceAttenuation", shell_distance_attenuation)
+			mat.set_shader_parameter("_Thickness", thickness)
+			mat.set_shader_parameter("_Attenuation", attenuation)
+			mat.set_shader_parameter("_OcclusionBias", occlusion_bias)
+			mat.set_shader_parameter("_ShellColor", shell_color)
+			mat.set_shader_parameter("_Density", density)
+	
+	mmi.cast_shadow = 1 if cast_shadow else 0
+
+func _ready():
+	var mat = ShaderMaterial.new()
+	#var mat2 = StandardMaterial3D.new()
+	mat.set_shader(preload("res://grass.gdshader"))
+	self._generate_mmi(self.shell_count, self, self.get_multimesh().mesh, mat, false)
+	
+	print("===== Shell Texturing =====")
+	print("Layers: ", self.shell_count)
+	print("Noise (min): ", self.noise_min)
+	print("Noise (max): ", self.noise_max)
+	print("Shell length: ", self.shell_length)
+	print("Shell count: ", self.shell_count)
+	print("Shell distance attenuation: ", self.shell_distance_attenuation)
+	print("Thickness: ", self.thickness)
+	print("Attenuation: ", self.attenuation)
+	print("Occlusion bias: ", self.occlusion_bias)
+	print("Shell color: ", self.shell_color)
+	print("Density: ", self.density)

multi_grass.tscn

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+[gd_scene load_steps=4 format=3 uid="uid://gbmju3x1gp7y"]
+
+[ext_resource type="Script" path="res://multi_grass.gd" id="1_f7cbg"]
+
+[sub_resource type="QuadMesh" id="QuadMesh_h8afx"]
+orientation = 1
+
+[sub_resource type="MultiMesh" id="MultiMesh_j6hjp"]
+transform_format = 1
+use_custom_data = true
+mesh = SubResource("QuadMesh_h8afx")
+
+[node name="multi_grass" type="MultiMeshInstance3D"]
+multimesh = SubResource("MultiMesh_j6hjp")
+script = ExtResource("1_f7cbg")

project.godot

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+; Engine configuration file.
+; It's best edited using the editor UI and not directly,
+; since the parameters that go here are not all obvious.
+;
+; Format:
+;   [section] ; section goes between []
+;   param=value ; assign values to parameters
+
+config_version=5
+
+[application]
+
+config/name="Shell Texturing"
+run/main_scene="res://main.tscn"
+config/features=PackedStringArray("4.2", "Forward Plus")
+config/icon="res://icon.png"
+
+[input]
+
+camera_rotate_button={
+"deadzone": 0.5,
+"events": [Object(InputEventMouseButton,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"button_mask":0,"position":Vector2(0, 0),"global_position":Vector2(0, 0),"factor":1.0,"button_index":3,"canceled":false,"pressed":false,"double_click":false,"script":null)
+]
+}
+camera_zoom_in={
+"deadzone": 0.5,
+"events": [Object(InputEventMouseButton,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"button_mask":0,"position":Vector2(0, 0),"global_position":Vector2(0, 0),"factor":1.0,"button_index":4,"canceled":false,"pressed":false,"double_click":false,"script":null)
+]
+}
+camera_zoom_out={
+"deadzone": 0.5,
+"events": [Object(InputEventMouseButton,"resource_local_to_scene":false,"resource_name":"","device":-1,"window_id":0,"alt_pressed":false,"shift_pressed":false,"ctrl_pressed":false,"meta_pressed":false,"button_mask":0,"position":Vector2(0, 0),"global_position":Vector2(0, 0),"factor":1.0,"button_index":5,"canceled":false,"pressed":false,"double_click":false,"script":null)
+]
+}