Make fossilization buttons' positioning account for screen distortion

src/general/utils/ScreenUtils.cs

@@ -26,16 +26,54 @@ public static Vector2 BarrelDistortion(Vector2 screenPos, float distortion, Vect
         // Convert from [0, size] to [0; 1]
         screenPos /= viewportSize;
 
-        Vector2 oversizeVector = Distort(new Vector2(1.0f, 1.0f), distortion);
-        oversizeVector = (oversizeVector + new Vector2(1.0f, 1.0f)) / 2.0f;
-        screenPos = RemapVector(screenPos, new Vector2(1.0f, 1.0f) - oversizeVector, oversizeVector);
+        Vector2 oversizeVector = Distort(Vector2.One, distortion);
+        oversizeVector = (oversizeVector + Vector2.One) / 2.0f;
+        screenPos = RemapVector(screenPos, Vector2.One - oversizeVector, oversizeVector);
 
         // Convert from [0, 1] to [-1; 1]
-        screenPos = (screenPos * 2.0f) - new Vector2(1.0f, 1.0f);
+        screenPos = (screenPos * 2.0f) - Vector2.One;
         screenPos = Distort(screenPos, distortion * 0.75f);
 
         // Return to [0, size]
-        screenPos = (screenPos + new Vector2(1.0f, 1.0f)) / 2.0f;
+        screenPos = (screenPos + Vector2.One) / 2.0f;
+        screenPos *= viewportSize;
+
+        return screenPos;
+    }
+
+    /// <summary>
+    ///   Finds a position at which <see cref="BarrelDistortion"/> returns a value equal to <paramref name="screenPos"/>
+    /// </summary>
+    /// <remarks>
+    ///   <para>
+    ///     This function is a rough approximation of the inverse function. Values of <paramref name="screenPos"/>
+    ///     outside the range of <paramref name="viewportSize"/> may produce very inaccurate results.
+    ///   </para>
+    /// </remarks>
+    public static Vector2 InverseBarrelDistortion(Vector2 screenPos, float distortion, Vector2 viewportSize)
+    {
+        Vector2 resolution = DisplayServer.WindowGetSize();
+
+        // The constant from shader calculations
+        const float distortionMultiplier = 75.0f;
+
+        distortion /= resolution.X;
+        distortion *= distortionMultiplier;
+
+        // Convert from [0, size] to [-1; 1]
+        screenPos /= viewportSize;
+        screenPos = screenPos * 2.0f - Vector2.One;
+
+        screenPos = InverseDistort(screenPos, distortion * 0.75f);
+
+        // Convert from [-1; 1] to [0, 1]
+        screenPos = (screenPos + Vector2.One) * 0.5f;
+
+        Vector2 oversizeVector = Distort(Vector2.One, distortion);
+        oversizeVector = (oversizeVector + Vector2.One) / 2.0f;
+        screenPos = InverseRemapVector(screenPos, Vector2.One - oversizeVector, oversizeVector);
+
+        // Return to [0, size]
         screenPos *= viewportSize;
 
         return screenPos;
@@ -54,11 +92,30 @@ private static Vector2 Distort(Vector2 pos, float distortion)
         return pos;
     }
 
+    private static Vector2 InverseDistort(Vector2 pos, float distortion)
+    {
+        float barrelDistortion1 = 0.1f * distortion;
+        float barrelDistortion2 = -0.025f * distortion;
+
+        // The following is a rough approximation of the inverse distortion formula.
+        // It works well enough on the [-1; 1] range, but shows weird behaviour outside of it.
+        float r2 = pos.X * pos.X + pos.Y * pos.Y;
+        r2 /= 1.0f + barrelDistortion1 * r2 + barrelDistortion2 * r2 * r2;
+        pos /= 1.0f + barrelDistortion1 * r2 + barrelDistortion2 * r2 * r2;
+
+        return pos;
+    }
+
     private static Vector2 RemapVector(Vector2 t, Vector2 a, Vector2 b)
     {
         t = (t - a) / (b - a);
         t.X = float.Clamp(t.X, 0.0f, 1.0f);
         t.Y = float.Clamp(t.Y, 0.0f, 1.0f);
         return t;
     }
+
+    private static Vector2 InverseRemapVector(Vector2 t, Vector2 a, Vector2 b)
+    {
+        return t * (b - a) + a;
+    }
 }

src/microbe_stage/MicrobeHUD.cs

@@ -267,6 +267,7 @@ protected override void ShowFossilisationButtons()
 
             var button = FossilisationButtonScene.Instantiate<FossilisationButton>();
             button.AttachedEntity = entity;
+            button.IsMicrobeStage = true;
             button.Connect(FossilisationButton.SignalName.OnFossilisationDialogOpened, new Callable(this,
                 nameof(ShowFossilisationDialog)));
 

src/thriveopedia/fossilisation/FossilisationButton.cs

@@ -17,6 +17,8 @@ public partial class FossilisationButton : TextureButton
     /// </summary>
     public Entity AttachedEntity;
 
+    public bool IsMicrobeStage;
+
     /// <summary>
     ///   Whether this species has already been fossilised.
     /// </summary>
@@ -70,7 +72,24 @@ public void UpdatePosition()
             return;
         }
 
-        GlobalPosition = camera.UnprojectPosition(AttachedEntity.Get<WorldPosition>().Position);
+        var canvasPosition = camera.UnprojectPosition(AttachedEntity.Get<WorldPosition>().Position);
+
+        if (IsMicrobeStage && Settings.Instance.ChromaticEnabled)
+        {
+            var viewportSize = GetViewportRect().Size;
+
+            // Clamping to the range where InverseBarrelDistortion is accurate
+            var tolerance = viewportSize * 0.1f;
+            canvasPosition = canvasPosition.Clamp(Vector2.Zero - tolerance, viewportSize + tolerance);
+
+            canvasPosition = ScreenUtils.InverseBarrelDistortion(
+                new Vector2(canvasPosition.X, viewportSize.Y - canvasPosition.Y), Settings.Instance.ChromaticAmount,
+                viewportSize);
+
+            canvasPosition = new Vector2(canvasPosition.X, viewportSize.Y - canvasPosition.Y);
+        }
+
+        GlobalPosition = canvasPosition;
     }
 
     private void OnPressed()