Smarter zoom - keep selected elements in sight

Greenshot/Drawing/DrawableContainerList.cs

@@ -235,6 +235,30 @@ namespace Greenshot.Drawing {
 			return false;
 		}
 
+		/// <summary>
+		/// A rectangle containing DrawingBounds of all drawableContainers in this list,
+		/// or empty rectangle if nothing is there.
+		/// </summary>
+		public Rectangle DrawingBounds
+		{
+			get
+			{
+				if (Count == 0)
+				{
+					return Rectangle.Empty;
+				}
+				else
+				{
+					var result = this[0].DrawingBounds;
+					for (int i = 1; i < Count; i++)
+					{
+						result = Rectangle.Union(result, this[i].DrawingBounds);
+					}
+					return result;
+				}
+			}
+		}
+
 		/// <summary>
 		/// Triggers all elements in the list ot be redrawn.
 		/// </summary>

Greenshot/Drawing/Surface.cs

@@ -1922,6 +1922,13 @@ namespace Greenshot.Drawing
 				);
 		}
 
+		/// <summary>
+		/// Get the rectangle bounding all selected elements (in surface coordinates space),
+		/// or empty rectangle if nothing is selcted.
+		/// </summary>
+		public Rectangle GetSelectionRectangle()
+			=> ToSurfaceCoordinates(selectedElements.DrawingBounds);
+
 		/// <summary>
 		/// Duplicate all the selecteded elements
 		/// </summary>

Greenshot/Forms/ImageEditorForm.cs

@@ -1580,21 +1580,37 @@ namespace Greenshot {
 			{
 				return;
 			}
+			if (value == Surface.ZoomFactor)
+			{
+				return;
+			}
 
-			// Store old scroll position
-			// When no scroll is currently needed - prefer top left corner.
-			var horizontalCenter = 0.0;
-			var verticalCenter = 0.0;
-			var rc = surface.GetVisibleRectangle();
+			// Store scroll position
+			var rc = surface.GetVisibleRectangle(); // use visible rc by default
 			var size = surface.Size;
-			if (size.Width > rc.Width)
+			if (value > Surface.ZoomFactor) // being smart on zoom-in
 			{
-				horizontalCenter = 1.0 * (rc.Left + rc.Width / 2) / size.Width;
-			}
-			if (size.Height > rc.Height)
-			{
-				verticalCenter = 1.0 * (rc.Top + rc.Height / 2) / size.Height;
+				var sel = surface.GetSelectionRectangle();
+				if (sel != Rectangle.Empty)
+				{
+					rc.Intersect(sel); // zoom to visible part of selection
+				}
+				else
+				{
+					// if image fits completely to currently visible rc and there are no things to focus on
+					// - prefer top left corner to zoom-in as less disorienting for screenshots
+					if (size.Width < rc.Width)
+					{
+						rc.Width = 0;
+					}
+					if (size.Height < rc.Height)
+					{
+						rc.Height = 0;
+					}
+				}
 			}
+			var horizontalCenter = 1.0 * (rc.Left + rc.Width / 2) / size.Width;
+			var verticalCenter = 1.0 * (rc.Top + rc.Height / 2) / size.Height;
 
 			// Set the new zoom value
 			Surface.ZoomFactor = value;

GreenshotPlugin/Interfaces/Drawing/Container.cs

@@ -145,6 +145,10 @@ namespace GreenshotPlugin.Interfaces.Drawing
 			get;
 			set;
 		}
+		Rectangle DrawingBounds
+		{
+			get;
+		}
 		void MakeBoundsChangeUndoable(bool allowMerge);
 		void Transform(Matrix matrix);
 		void MoveBy(int dx, int dy);