Add: simple shaders, following Book of Shaders page 6

src/simple_hsb_func/HSBField_polar.gdshader

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+shader_type canvas_item;
+
+#define TWO_PI 6.28318530718
+
+uniform vec2 resolution = vec2(40,40);
+uniform vec2 u_resolution;
+uniform float u_time;
+
+//  Function from Iñigo Quiles
+//  https://www.shadertoy.com/view/MsS3Wc
+vec3 hsb2rgb( in vec3 c ){
+    vec3 rgb = clamp(abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),
+                             6.0)-3.0)-1.0,
+                     0.0,
+                     1.0 );
+    rgb = rgb*rgb*(3.0-2.0*rgb);
+    return c.z * mix( vec3(1.0), rgb, c.y);
+}
+
+void fragment() {
+	// Called for every pixel the material is visible on.
+	vec2 st = UV/resolution;
+	vec3 color = vec3(0.0);
+	
+	vec2 toCenter = vec2(0.5) - UV;
+	float angle = pow(atan(toCenter.y, toCenter.x), 1.0);
+	float radius = length(toCenter)*2.0;
+	
+	float normHue = (angle/TWO_PI)+0.5;
+	normHue = pow(normHue, 3.0);
+	
+	color = hsb2rgb(vec3(normHue,radius,1.0));
+	
+	COLOR = vec4(color, 1.0);
+	
+}
+
+//void light() {
+//	// Called for every pixel for every light affecting the CanvasItem.
+//	// Uncomment to replace the default light processing function with this one.
+//}

src/simple_hsb_func/HSBField_polar.gdshader.uid

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+uid://b1avd7otwdbqx

src/simple_hsb_func/HSBField_polar.tscn

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+[gd_scene load_steps=3 format=3 uid="uid://dk1hun66hk76t"]
+
+[ext_resource type="Shader" uid="uid://b1avd7otwdbqx" path="res://src/simple_hsb_func/HSBField_polar.gdshader" id="1_y6vnc"]
+
+[sub_resource type="ShaderMaterial" id="ShaderMaterial_s1hel"]
+shader = ExtResource("1_y6vnc")
+shader_parameter/resolution = Vector2(40, 40)
+shader_parameter/u_resolution = Vector2(0, 0)
+shader_parameter/u_time = 0.0
+
+[node name="HsbField" type="Control"]
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+
+[node name="ColorRect" type="ColorRect" parent="."]
+material = SubResource("ShaderMaterial_s1hel")
+layout_mode = 0
+offset_right = 40.0
+offset_bottom = 40.0

src/simple_hsb_func/HSB_Field_non_polar.gdshader

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+shader_type canvas_item;
+
+uniform vec2 u_resolution = vec2(40.0,40.0);
+uniform float u_time;
+
+vec3 rgb2hsb( in vec3 c ){
+    vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
+    vec4 p = mix(vec4(c.bg, K.wz),
+                 vec4(c.gb, K.xy),
+                 step(c.b, c.g));
+    vec4 q = mix(vec4(p.xyw, c.r),
+                 vec4(c.r, p.yzx),
+                 step(p.x, c.r));
+    float d = q.x - min(q.w, q.y);
+    float e = 1.0e-10;
+    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)),
+                d / (q.x + e),
+                q.x);
+}
+
+//  Function from Iñigo Quiles
+//  https://www.shadertoy.com/view/MsS3Wc
+vec3 hsb2rgb( in vec3 c ){
+    vec3 rgb = clamp(abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),
+                             6.0)-3.0)-1.0,
+                     0.0,
+                     1.0 );
+    rgb = rgb*rgb*(3.0-2.0*rgb);
+    return c.z * mix(vec3(1.0), rgb, c.y);
+}
+
+void fragment() {
+	vec3 color = vec3(0.0);
+	
+	color = hsb2rgb(vec3(UV.x, 1.0, UV.y));
+	COLOR = vec4(color, 1.0);
+}

src/simple_hsb_func/HSB_Field_non_polar.gdshader.uid

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+uid://res5r3cil0uv

src/simple_hsb_func/HSB_Field_non_polar.tscn

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+[gd_scene load_steps=3 format=3 uid="uid://8g28bhlvay61"]
+
+[ext_resource type="Shader" uid="uid://res5r3cil0uv" path="res://src/simple_hsb_func/HSB_Field_non_polar.gdshader" id="1_c8wtv"]
+
+[sub_resource type="ShaderMaterial" id="ShaderMaterial_e0bhl"]
+shader = ExtResource("1_c8wtv")
+shader_parameter/u_resolution = Vector2(0, 0)
+shader_parameter/u_time = 0.0
+
+[node name="HsbFieldNonPolar" type="Control"]
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+
+[node name="ColorRect" type="ColorRect" parent="."]
+material = SubResource("ShaderMaterial_e0bhl")
+layout_mode = 0
+offset_right = 40.0
+offset_bottom = 40.0