|VFX] Blackboard not visible when docked in small area

Jira: UUM-65513

Reproduction steps:
1. Open the attached “VFX.zip” project
2. Open the “graph” asset from the Project Window
3. Dock the “graph” Window to the bottom of the UI

Expected result: Floating panel is visible
Actual result: Floating panel disappears

Reproducible with: 2021.3.35f1, 2022.3.21f1, 2023.2.0a23, 2023.2.13f1
Not reproducible with: 2023.3.0b10
Fixed in: 2023.3.0a2

Reproducible on: Windows 11
Not reproducible on: no other environment tested

Note:
The 2023.3.0a1 version does not exist therefore cannot be tested
Reproducible on any new project
Issue appears if the floating panel is placed in the bottom left corner
Downgrading from versions where it worked correctly, would usually fix the issue

![video](https://jira.unity3d.com/secure/attachment/1397173/IN-69565%20repro.mkv)

Author: julienamsellem

Packages/com.unity.visualeffectgraph/Editor/GraphView/VFXComponentBoard.cs

@@ -4,9 +4,7 @@
 using System.Globalization;
 using UnityEditor.Experimental;
 using UnityEditor.Experimental.GraphView;
-using UnityEditor.SceneManagement;
 
-using UnityEditor.VFX.UIElements;
 using UnityEngine;
 using UnityEngine.VFX;
 using UnityEngine.UIElements;
@@ -71,51 +69,25 @@ public static void SavePosition(Board board, Rect r)
 
         public static void ValidatePosition(GraphElement element, VFXView view, Rect defaultPosition)
         {
-            Rect viewrect = view.contentRect;
-            Rect rect = element.GetPosition();
-            bool changed = false;
+            var viewrect = view.contentRect;
+            var rect = element.GetPosition();
+            var changed = false;
 
-            Vector2 maxSizeInView = viewrect.max;
-            float newWidth = Mathf.Max(defaultPosition.width, Mathf.Min(rect.width, maxSizeInView.x));
-            float newHeight = Mathf.Max(defaultPosition.height, Mathf.Min(rect.height, maxSizeInView.y));
-
-            if (Mathf.Abs(newWidth - rect.width) > 1)
-            {
-                rect.width = newWidth;
-                changed = true;
-            }
-
-            if (Mathf.Abs(newHeight - rect.height) > 1)
+            if (rect.xMin > viewrect.xMax || rect.xMax > viewrect.xMax)
             {
-                rect.height = newHeight;
+                var width = Math.Max(Math.Min(rect.width, viewrect.width), element.resolvedStyle.minWidth.value);
+                rect.xMax = viewrect.xMax;
+                rect.xMin = Math.Max(0, rect.xMax - width);
+                rect.width = width;
                 changed = true;
             }
 
-            var xDiff = viewrect.xMax - rect.xMax;
-            if (xDiff < 0)
+            if (rect.yMin > viewrect.yMax || rect.yMax > viewrect.yMax)
             {
-                if (rect.x + xDiff >= 0)
-                {
-                    rect.x += xDiff;
-                }
-                else
-                {
-                    rect.width = Math.Max(defaultPosition.width, rect.width + xDiff);
-                }
-                changed = true;
-            }
-
-            var yDiff = viewrect.yMax - rect.yMax;
-            if (yDiff < 0)
-            {
-                if (rect.y + yDiff >= 0)
-                {
-                    rect.y += yDiff;
-                }
-                else
-                {
-                    rect.height = Math.Max(defaultPosition.height, rect.height + yDiff);
-                }
+                var height = Math.Max(Math.Min(rect.height, viewrect.height), element.resolvedStyle.minHeight.value);
+                rect.yMax = viewrect.yMax;
+                rect.yMin = Math.Max(0, rect.yMax - height);
+                rect.height = height;
                 changed = true;
             }
 

Packages/com.unity.visualeffectgraph/Editor/UIResources/uss/VFXBlackboard.uss

@@ -1,11 +1,13 @@
 VFXBlackboard.blackboard
 {
     background-color: #292929;
+    min-height: 200px;
+    min-width: 250px;
 }
 
 /* This margin is to leave some space around the blackboard for the resizer element to grab the mouse */
 VFXBlackboard.blackboard .mainContainer {
-    margin: 1px 3px;
+    margin: 4px;
 }
 
 VFXBlackboard.blackboard > .mainContainer > #content > #header {

Packages/com.unity.visualeffectgraph/Editor/UIResources/uss/VFXComponentBoard.uss

@@ -9,6 +9,7 @@ VFXComponentBoard.graphElement
 
 VFXComponentBoard.graphElement > .mainContainer
 {
+    margin: 4px;
     flex: 1 1 auto;
     background-color: #2b2b2b;
     border-color: #191919;