Scale Shift+wheel brush resize geometrically

Replace the fixed additive brush-size step with a fraction of the current
size, so small brushes resize a texel at a time (fine control) while large
ones jump in bigger increments. Always moves at least one texel per notch.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/Scripts/MeshPainter.cs

@@ -204,8 +204,11 @@ public partial class MeshPainter : MonoBehaviour
     [Range(1, 256)]
     public int brushSize = 16;
 
-    [Tooltip("Texels added/removed per mouse-wheel notch while Shift is held (paint mode brush resize).")]
-    public int brushSizeScrollStep = 4;
+    [Tooltip("Fraction of the current brush size added/removed per mouse-wheel notch while Shift is held. " +
+             "The step scales with the size, so small brushes resize slowly (fine control) and large ones " +
+             "resize faster. Always moves at least one texel per notch.")]
+    [Range(0.01f, 1f)]
+    public float brushSizeScrollFactor = 0.15f;
 
     /// <summary>
     /// Raised after Shift+wheel changes <see cref="brushSize"/> so the in-game HUD can re-sync its
@@ -1108,7 +1111,9 @@ public partial class MeshPainter : MonoBehaviour
         float scroll = ReadScroll();
         if (Mathf.Approximately(scroll, 0f)) return;
 
-        int step = Mathf.Max(1, brushSizeScrollStep);
+        // Geometric resize: the step scales with the current size, so small brushes change a texel
+        // at a time (fine control) while large brushes jump in bigger increments. Min one texel.
+        int step = Mathf.Max(1, Mathf.RoundToInt(brushSize * brushSizeScrollFactor));
         int next = Mathf.Clamp(brushSize + (int)Mathf.Sign(scroll) * step, 1, 256);
         if (next == brushSize) return;