Speed up slideshow loading

Vocaluxe/Base/CMain.cs

@@ -453,6 +453,11 @@ namespace Vocaluxe.Base
             return CDraw.AddTexture(fileName);
         }
 
+        public CTextureRef EnqueueTexture(string fileName)
+        {
+            return CDraw.EnqueueTexture(fileName);
+        }
+
         public void RemoveTexture(ref CTextureRef texture)
         {
             CDraw.RemoveTexture(ref texture);

VocaluxeLib/IBasic.cs

@@ -151,6 +151,7 @@ namespace VocaluxeLib
         void DrawTextureReflection(CTextureRef texture, SRectF rect, SColorF color, SRectF bounds, float reflectionSpace, float reflectionHeight);
 
         CTextureRef AddTexture(string fileName);
+        CTextureRef EnqueueTexture(string fileName);
         void RemoveTexture(ref CTextureRef texture);
 
         void DrawRect(SColorF color, SRectF rect);

VocaluxeLib/Menu/CBackground.cs

@@ -189,7 +189,7 @@ namespace VocaluxeLib.Menu
             _Theme.Type = EBackgroundTypes.SlideShow;
             if (!String.IsNullOrEmpty(image))
             {
-                CTextureRef texture = CBase.Drawing.AddTexture(image);
+                CTextureRef texture = _SlideShowTextures.Count == 0 ? CBase.Drawing.AddTexture(image) : CBase.Drawing.EnqueueTexture(image);
                 if (texture != null)
                     _SlideShowTextures.Add(texture);
             }