Scrollable controls expose a new property IScrollInfo.NumberOfVisibleLines that will be used for limiting MouseWheelScrolling

Author: morpheusxx

MediaPortal/Source/UI/SkinEngine/Controls/Panels/StackPanel.cs

@@ -824,6 +824,16 @@ public virtual bool IsViewPortAtRight
       get { return Orientation == Orientation.Vertical || _actualLastVisibleChildIndex == GetVisibleChildren().Count - 1; }
     }
 
+    public int NumberOfVisibleLines
+    {
+      get
+      {
+        int numLines = 0;
+        CalcHelper.Bound(ref numLines, 0, _actualLastVisibleChildIndex - _actualFirstVisibleChildIndex);
+        return numLines > 0 ? numLines : 0;
+      }
+    }
+
     #endregion
   }
 }

MediaPortal/Source/UI/SkinEngine/Controls/Panels/UniformGrid.cs

@@ -568,6 +568,11 @@ public bool IsViewPortAtRight
       get { return _scrollIndexX + _actualNumVisibleCols == _actualColumns; }
     }
 
+    public int NumberOfVisibleLines
+    {
+      get { return _actualNumVisibleRows; }
+    }
+
     #endregion
   }
 }

MediaPortal/Source/UI/SkinEngine/Controls/Panels/WrapPanel.cs

@@ -110,7 +110,7 @@ public static LineMeasurement Create()
     protected IList<LineMeasurement> _arrangedLines = new List<LineMeasurement>();
     protected int _actualFirstVisibleLineIndex = 0;
     protected int _actualLastVisibleLineIndex = -1;
-    
+
     #endregion
 
     #region Ctor
@@ -990,6 +990,11 @@ public virtual bool IsViewPortAtRight
       get { return Orientation == Orientation.Horizontal || _actualLastVisibleLineIndex == GetVisibleChildren().Count - 1; }
     }
 
+    public int NumberOfVisibleLines
+    {
+      get { return _actualLastVisibleLineIndex - _actualFirstVisibleLineIndex + 1; }
+    }
+
     #endregion
   }
 }

MediaPortal/Source/UI/SkinEngine/Controls/Visuals/IScrollInfo.cs

@@ -22,6 +22,8 @@ You should have received a copy of the GNU General Public License
 
 #endregion
 
+using System.Windows.Forms;
+
 namespace MediaPortal.UI.SkinEngine.Controls.Visuals
 {
   /// <summary>
@@ -113,5 +115,12 @@ public interface IScrollInfo
     /// Returns the information if the viewport is at the right side of the available area.
     /// </summary>
     bool IsViewPortAtRight { get; }
+
+    /// <summary>
+    /// Returns the number of lines that can be shown inside the viewport. This value can be used for calculating 
+    /// the number of lines to be scrolled when using mouse wheel. If this value is <c>0</c>, the system default 
+    /// scrolling will be used (usually scrolling by <seealso cref="SystemInformation.MouseWheelScrollLines"/>).
+    /// </summary>
+    int NumberOfVisibleLines { get; }
   }
 }

MediaPortal/Source/UI/SkinEngine/Controls/Visuals/ItemsPresenter.cs

@@ -379,7 +379,7 @@ public bool IsViewPortAtTop
       get
       {
         IScrollInfo si = _itemsHostPanel as IScrollInfo;
-        return si == null ? true : si.IsViewPortAtTop;
+        return si == null || si.IsViewPortAtTop;
       }
     }
 
@@ -410,6 +410,15 @@ public bool IsViewPortAtRight
       }
     }
 
+    public int NumberOfVisibleLines
+    {
+      get
+      {
+        IScrollInfo si = _itemsHostPanel as IScrollInfo;
+        return si == null ? 0 : si.NumberOfVisibleLines;
+      }
+    }
+
     #endregion
   }
 }

MediaPortal/Source/UI/SkinEngine/Controls/Visuals/ScrollContentPresenter.cs

@@ -154,7 +154,7 @@ public override void BringIntoView(UIElement element, RectangleF elementBounds)
         if (IsHorzCentering)
           differenceX = CalculateCenteredScrollPos(elementBounds.X, elementBounds.Width, ActualPosition.X, ActualWidth);
         else if (_doScroll)
-          differenceX = CalculateVisibleScrollDifference(elementBounds.X, elementBounds.Width, ActualPosition.X, ActualWidth); 
+          differenceX = CalculateVisibleScrollDifference(elementBounds.X, elementBounds.Width, ActualPosition.X, ActualWidth);
 
         if (IsVertCentering)
           differenceY = CalculateCenteredScrollPos(elementBounds.Y, elementBounds.Height, ActualPosition.Y, ActualHeight) - _actualScrollOffsetY;
@@ -173,7 +173,7 @@ protected float CalculateVisibleScrollDifference(double elementPos, double eleme
     {
       double difference = 0.0f;
       if (elementPos + elementSize > actualPos + actualSize)
-        difference = - (elementPos + elementSize - actualPos - actualSize);
+        difference = -(elementPos + elementSize - actualPos - actualSize);
       if (elementPos + difference < actualPos)
         difference = actualPos - elementPos;
       return (float) difference;
@@ -260,7 +260,7 @@ public override void Render(RenderContext parentRenderContext)
     {
       if (OpacityMask == null && (TotalHeight > ActualHeight || TotalWidth > ActualWidth))
       {
-        SolidColorBrush brush = new SolidColorBrush {Color = Color.Black};
+        SolidColorBrush brush = new SolidColorBrush { Color = Color.Black };
         OpacityMask = brush;
         _forcedOpacityMask = true;
       }
@@ -288,7 +288,7 @@ public override void SaveUIState(IDictionary<string, object> state, string prefi
       base.SaveUIState(state, prefix);
       state[prefix + "/ScrollOffsetX"] = _scrollOffsetX;
       state[prefix + "/ScrollOffsetY"] = _scrollOffsetX;
-  }
+    }
 
     public override void RestoreUIState(IDictionary<string, object> state, string prefix)
     {
@@ -450,7 +450,7 @@ public bool FocusPageDown()
       {
         if (currentElement.ActualPosition.Y + currentElement.ActualHeight + DELTA_DOUBLE > ActualPosition.Y + ActualHeight)
           // Already at bottom
-          limitPosition = (float) (ActualPosition.Y + 2*ActualHeight);
+          limitPosition = (float) (ActualPosition.Y + 2 * ActualHeight);
         else
           limitPosition = (float) (ActualPosition.Y + ActualHeight);
       }
@@ -526,7 +526,7 @@ public bool FocusPageRight()
       {
         if (currentElement.ActualPosition.X + ActualWidth + DELTA_DOUBLE > ActualPosition.X + ActualWidth)
           // Already at right
-          limitPosition = (float) (ActualPosition.X + 2*ActualWidth);
+          limitPosition = (float) (ActualPosition.X + 2 * ActualWidth);
         else
           limitPosition = (float) (ActualPosition.X + ActualWidth);
       }
@@ -651,6 +651,11 @@ public bool IsViewPortAtRight
       get { return TemplateControl == null || -_actualScrollOffsetX + ActualWidth + DELTA_DOUBLE >= TotalWidth; }
     }
 
+    public int NumberOfVisibleLines
+    {
+      get { return 0; /* As we are scrolling only by pixels here, we keep the default behavior */ }
+    }
+
     #endregion
   }
 }

MediaPortal/Source/UI/SkinEngine/Controls/Visuals/ScrollViewer.cs

@@ -390,19 +390,22 @@ public override void OnMouseWheel(int numDetents)
       if (!IsMouseOver)
         return;
 
-      int numLines = numDetents * SystemInformation.MouseWheelScrollLines;
+      IScrollViewerFocusSupport svfs = FindScrollControl() as IScrollViewerFocusSupport;
+      if (svfs == null)
+        return;
+
+      int scrollByLines = SystemInformation.MouseWheelScrollLines; // Use the system setting as default.
+      
+      IScrollInfo scrollInfo = svfs as IScrollInfo;
+      if (scrollInfo != null && scrollInfo.NumberOfVisibleLines != 0) // If ScrollControl can shown less items, use this as limit.
+        scrollByLines = scrollInfo.NumberOfVisibleLines;
+
+      int numLines = numDetents * scrollByLines;
+      
       if (numLines < 0)
-      {
-        IScrollViewerFocusSupport svfs = FindScrollControl() as IScrollViewerFocusSupport;
-        if (svfs != null)
-          svfs.ScrollDown(-1 * numLines);
-      }
+        svfs.ScrollDown(-1*numLines);
       else if (numLines > 0)
-      {
-        IScrollViewerFocusSupport svfs = FindScrollControl() as IScrollViewerFocusSupport;
-        if (svfs != null)
-          svfs.ScrollUp(numLines);
-      }
+        svfs.ScrollUp(numLines);
     }
 
     public override void OnKeyPressed(ref Key key)