Ignore terrain slopes when calculating model shadows.

This is less realistic, but better matches the original
game and is the only practical way to reduce visual issues
caused by long shadows being cast over multiple cells.

OpenRA.Mods.Common/Graphics/UIModelRenderable.cs

@@ -68,7 +68,6 @@ namespace OpenRA.Mods.Common.Graphics
 		public IRenderable OffsetBy(in WVec vec) { return this; }
 		public IRenderable AsDecoration() { return this; }
 
-		static readonly float[] GroundNormal = { 0, 0, 1, 1 };
 		public IFinalizedRenderable PrepareRender(WorldRenderer wr)
 		{
 			return new FinalizedUIModelRenderable(wr, this);
@@ -85,7 +84,7 @@ namespace OpenRA.Mods.Common.Graphics
 				var draw = model.models.Where(v => v.IsVisible);
 
 				renderProxy = Game.Renderer.WorldModelRenderer.RenderAsync(
-					wr, draw, model.camera, model.scale, GroundNormal, model.lightSource,
+					wr, draw, model.camera, model.scale, WRot.None, model.lightSource,
 					model.lightAmbientColor, model.lightDiffuseColor,
 					model.palette, model.normalsPalette, model.shadowPalette);
 			}