[ShaderGraph][2021.2] Update rectangle node to better handle detail at a distance (#3405)

* Fix for 1156801 - erroneous edge pixels generated by rectangle node
    - Existing method doesn't handle large screen space derivatives well
    - Add a new control to the rectangle node to switch between methods
    - Existing method is "fastest" and the new method is "nicest"
    - Test project uses default of "fastest", but users can pick "nicest"
      for best results.
* Add documentation and changelog entry for the new Rectangle Node control
* Add updated thumbnail image for Rectangle node

Author: jessebarker

com.unity.shadergraph/CHANGELOG.md

@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Node included HLSL files are now tracked more robustly, so they work after file moves and renames [1301915] (https://issuetracker.unity3d.com/product/unity/issues/guid/1301915/)
 - Clean up console error reporting from node shader compilation so errors are reported in the graph rather than the Editor console [1296291] (https://issuetracker.unity3d.com/product/unity/issues/guid/1296291/)
 - Fixed treatment of node precision in subgraphs, now allows subgraphs to switch precisions based on the subgraph node [1304050] (https://issuetracker.unity3d.com/issues/precision-errors-when-theres-a-precision-discrepancy-between-subgraphs-and-parent-graphs)
+- Fixed an issue where the Rectangle Node could lose detail at a distance.  New control offers additional method that preserves detail better [1156801]
 
 ## [11.0.0] - 2020-10-21
 

com.unity.shadergraph/Documentation~/Rectangle-Node.md

@@ -15,6 +15,12 @@ NOTE: This [Node](Node.md) can only be used in the **Fragment** [Shader Stage](S
 | Height      | Input | Float    | None | Rectangle height |
 | Out | Output      |    Float    | None | Output value |
 
+## Controls
+
+| Name        | Type           | Options  | Description |
+|:------------ |:-------------|:-----|:---|
+|      | Dropdown | Fastest, Nicest | Robustness of computation |
+
 ## Generated Code Example
 
 The following example code represents one possible outcome of this node.

com.unity.shadergraph/Documentation~/images/RectangleNodeThumb.png

@@ -1,8 +1,16 @@
 using System.Reflection;
 using UnityEngine;
+using UnityEditor.Graphing;
+using UnityEditor.ShaderGraph.Drawing.Controls;
 
 namespace UnityEditor.ShaderGraph
 {
+    enum ClampType
+    {
+        Fastest,
+        Nicest
+    };
+
     [Title("Procedural", "Shape", "Rectangle")]
     class RectangleNode : CodeFunctionNode
     {
@@ -11,12 +19,36 @@ public RectangleNode()
             name = "Rectangle";
         }
 
+        [SerializeField]
+        private ClampType m_ClampType = ClampType.Fastest;
+
+        [EnumControl("")]
+        public ClampType clampType
+        {
+            get { return m_ClampType; }
+            set
+            {
+                if (m_ClampType == value)
+                    return;
+
+                m_ClampType = value;
+                Dirty(ModificationScope.Graph);
+            }
+        }
+
         protected override MethodInfo GetFunctionToConvert()
         {
-            return GetType().GetMethod("Unity_Rectangle", BindingFlags.Static | BindingFlags.NonPublic);
+            switch (clampType)
+            {
+                case ClampType.Nicest:
+                    return GetType().GetMethod("Unity_Rectangle_Nicest", BindingFlags.Static | BindingFlags.NonPublic);
+                case ClampType.Fastest:
+                default:
+                    return GetType().GetMethod("Unity_Rectangle_Fastest", BindingFlags.Static | BindingFlags.NonPublic);
+            }
         }
 
-        static string Unity_Rectangle(
+        static string Unity_Rectangle_Fastest(
             [Slot(0, Binding.MeshUV0)] Vector2 UV,
             [Slot(1, Binding.None, 0.5f, 0, 0, 0)] Vector1 Width,
             [Slot(2, Binding.None, 0.5f, 0, 0, 0)] Vector1 Height,
@@ -28,6 +60,25 @@ static string Unity_Rectangle(
     $precision2 d = abs(UV * 2 - 1) - $precision2(Width, Height);
     d = 1 - d / fwidth(d);
     Out = saturate(min(d.x, d.y));
+}";
+        }
+
+        static string Unity_Rectangle_Nicest(
+            [Slot(0, Binding.MeshUV0)] Vector2 UV,
+            [Slot(1, Binding.None, 0.5f, 0, 0, 0)] Vector1 Width,
+            [Slot(2, Binding.None, 0.5f, 0, 0, 0)] Vector1 Height,
+            [Slot(3, Binding.None, ShaderStageCapability.Fragment)] out Vector1 Out)
+        {
+            return
+@"
+{
+    UV = UV * 2.0 - 1.0;
+    $precision2 w = $precision2(Width, Height);     // rectangle width/height
+    $precision2 f = min(fwidth(UV), 0.5f);
+    $precision2 k = 1.0f / f;
+    $precision2 o = saturate(0.5f + k * (w - abs(UV)));
+    o = min(o, k * w * 2.0f);
+    Out = o.x * o.y;
 }";
         }
     }