basic TransformPoint work

BizHawk.Client.EmuHawk/DisplayManager/DisplayManager.cs

@@ -247,6 +247,20 @@ namespace BizHawk.Client.EmuHawk
 			return new Point((int)v.X, (int)v.Y);
 		}
 
+		/// <summary>
+		/// Using the current filter program, turn a emulator screen space coordinat to a window coordinate (suitable for lua layer drawing)
+		/// </summary>
+		public Point TransformPoint(Point p)
+		{
+			//now, if theres no filter program active, just give up
+			if (CurrentFilterProgram == null) return p;
+
+			//otherwise, have the filter program untransform it
+			Vector2 v = new Vector2(p.X, p.Y);
+			v = CurrentFilterProgram.TransformPoint("default", v);
+			return new Point((int)v.X, (int)v.Y);
+		}
+
 
 		/// <summary>
 		/// This will receive an emulated output frame from an IVideoProvider and run it through the complete frame processing pipeline

BizHawk.Client.EmuHawk/DisplayManager/FilterManager.cs

@@ -94,6 +94,19 @@ namespace BizHawk.Client.EmuHawk.FilterManager
 			return point;
 		}
 
+		/// <summary>
+		/// Receives a point in the input space of the filter program and transforms it through to output points
+		/// </summary>
+		public Vector2 TransformPoint(string channel, Vector2 point)
+		{
+			for (int i = 0; i < Filters.Count; i++)
+			{
+				var filter = Filters[i];
+				point = filter.TransformPoint(channel, point);
+			}
+			return point;
+		}
+
 		public class ProgramStep
 		{
 			public ProgramStep(ProgramStepType type, object args, string comment = null)

BizHawk.Client.EmuHawk/DisplayManager/Filters/BaseFilter.cs

@@ -51,6 +51,20 @@ namespace BizHawk.Client.EmuHawk.Filters
 			}
 			return point;
 		}
+
+		public virtual Vector2 TransformPoint(string channel, Vector2 point)
+		{
+			//base class behaviour here just uses the input and output sizes, if appropriate. few filters will have to do anything more complex
+			var input = FindInput(channel);
+			var output = FindOutput(channel);
+			if (input != null && output != null)
+			{
+				point.X *= ((float)output.SurfaceFormat.Size.Width) / (float)input.SurfaceFormat.Size.Width;
+				point.Y *= ((float)output.SurfaceFormat.Size.Height) / (float)input.SurfaceFormat.Size.Height;
+			}
+			return point;
+		}
+
 		public void SetInput(Texture2d tex)
 		{
 			InputTexture = tex;

BizHawk.Client.EmuHawk/DisplayManager/Filters/Gui.cs

@@ -232,6 +232,17 @@ namespace BizHawk.Client.EmuHawk.Filters
 			return point;
 		}
 
+		public override Vector2 TransformPoint(string channel, Vector2 point)
+		{
+			if (nop)
+				return point;
+			point.X *= LL.WidthScale;
+			point.Y *= LL.HeightScale;
+			point.X += LL.vx;
+			point.Y += LL.vy;
+			return point;
+		}
+
 		public override void Run()
 		{
 			if (nop)