Centre file previews in directory previews.

GalleryShare/Extensions.cs

@@ -13,6 +13,14 @@ namespace GalleryShare
 			);
 		}
 
+		public static PointF Add(this PointF a, PointF b)
+		{
+			return new PointF(
+				a.X + b.X,
+				a.Y + b.Y
+			);
+		}
+
 		public static Point ToIntPoint(this PointF source)
 		{
 			return new Point((int)source.X, (int)source.Y);

GalleryShare/ThumbnailGenerator.cs

@@ -57,6 +57,10 @@ namespace GalleryShare
 							continue;
 						}
 						PointF drawingPos = getDirectoryImageDrawPosition(i - filesSkipped).Multiply(new PointF(resultImage.Width, resultImage.Height));
+						drawingPos = drawingPos.Add(new PointF(
+							thumbnailSize.Width / 4f - fileThumbnail.Width / 2f,
+							thumbnailSize.Height / 4f - fileThumbnail.Height / 2f
+						));
 						context.DrawImage(fileThumbnail, drawingPos.ToIntPoint());
 					}
 				}