Pass depth scale factors to vertex shaders.

OpenRA.Game/Game.cs

@@ -359,6 +359,9 @@ namespace OpenRA
 			ModData.InitializeLoaders(ModData.DefaultFileSystem);
 			Renderer.InitializeFonts(ModData);
 
+			var grid = ModData.Manifest.Contains<MapGrid>() ? ModData.Manifest.Get<MapGrid>() : null;
+			Renderer.InitializeDepthBuffer(grid);
+
 			if (Cursor != null)
 				Cursor.Dispose();
 

OpenRA.Game/Graphics/SpriteRenderer.cs

@@ -114,11 +114,17 @@ namespace OpenRA.Graphics
 			shader.SetTexture("Palette", palette);
 		}
 
-		public void SetViewportParams(Size screen, float zoom, int2 scroll)
+		public void SetViewportParams(Size screen, float depthScale, float depthOffset, float zoom, int2 scroll)
 		{
-			shader.SetVec("Scroll", scroll.X, scroll.Y);
-			shader.SetVec("r1", zoom * 2f / screen.Width, -zoom * 2f / screen.Height);
-			shader.SetVec("r2", -1, 1);
+			shader.SetVec("Scroll", scroll.X, scroll.Y, scroll.Y);
+			shader.SetVec("r1",
+				zoom * 2f / screen.Width,
+				-zoom * 2f / screen.Height,
+				-depthScale * zoom / screen.Height);
+			shader.SetVec("r2", -1, 1, 1 - depthOffset);
+
+			// Texture index is sampled as a float, so convert to pixels then scale
+			shader.SetVec("DepthTextureScale", 128 * depthScale * zoom / screen.Height);
 		}
 
 		public void SetDepthPreviewEnabled(bool enabled)

OpenRA.Game/Map/MapGrid.cs

@@ -28,6 +28,8 @@ namespace OpenRA
 
 		public readonly int MaximumTileSearchRange = 50;
 
+		public readonly bool EnableDepthBuffer = false;
+
 		public readonly WVec[] SubCellOffsets =
 		{
 			new WVec(0, 0, 0),       // full cell - index 0

OpenRA.Game/Renderer.cs

@@ -40,6 +40,9 @@ namespace OpenRA
 
 		SheetBuilder fontSheetBuilder;
 
+		float depthScale;
+		float depthOffset;
+
 		Size? lastResolution;
 		int2? lastScroll;
 		float? lastZoom;
@@ -102,6 +105,20 @@ namespace OpenRA
 			}
 		}
 
+		public void InitializeDepthBuffer(MapGrid mapGrid)
+		{
+			// The depth buffer needs to be initialized with enough range to cover:
+			//  - the height of the screen
+			//  - the z-offset of tiles from MaxTerrainHeight below the bottom of the screen (pushed into view)
+			//  - additional z-offset from actors on top of MaxTerrainHeight terrain
+			//  - a small margin so that tiles rendered partially above the top edge of the screen aren't pushed behind the clip plane
+			// We need an offset of mapGrid.MaximumTerrainHeight * mapGrid.TileSize.Height / 2 to cover the terrain height
+			// and choose to use mapGrid.MaximumTerrainHeight * mapGrid.TileSize.Height / 4 for each of the actor and top-edge cases
+			this.depthScale = mapGrid == null || !mapGrid.EnableDepthBuffer ? 0 :
+				(float)Resolution.Height / (Resolution.Height + mapGrid.TileSize.Height * mapGrid.MaximumTerrainHeight);
+			this.depthOffset = this.depthScale / 2;
+		}
+
 		public void BeginFrame(int2 scroll, float zoom)
 		{
 			Device.Clear();
@@ -115,8 +132,8 @@ namespace OpenRA
 			if (resolutionChanged)
 			{
 				lastResolution = Resolution;
-				RgbaSpriteRenderer.SetViewportParams(Resolution, 1f, int2.Zero);
-				SpriteRenderer.SetViewportParams(Resolution, 1f, int2.Zero);
+				RgbaSpriteRenderer.SetViewportParams(Resolution, 0f, 0f, 1f, int2.Zero);
+				SpriteRenderer.SetViewportParams(Resolution, 0f, 0f, 1f, int2.Zero);
 				RgbaColorRenderer.SetViewportParams(Resolution, 1f, int2.Zero);
 			}
 
@@ -125,8 +142,8 @@ namespace OpenRA
 			{
 				lastScroll = scroll;
 				lastZoom = zoom;
-				WorldRgbaSpriteRenderer.SetViewportParams(Resolution, zoom, scroll);
-				WorldSpriteRenderer.SetViewportParams(Resolution, zoom, scroll);
+				WorldRgbaSpriteRenderer.SetViewportParams(Resolution, depthScale, depthOffset, zoom, scroll);
+				WorldSpriteRenderer.SetViewportParams(Resolution, depthScale, depthOffset, zoom, scroll);
 				WorldVoxelRenderer.SetViewportParams(Resolution, zoom, scroll);
 				WorldRgbaColorRenderer.SetViewportParams(Resolution, zoom, scroll);
 			}