Implement blending enable/disable for IGL_GDIPlus (more just moving it away from GDIPlusGuiRenderer)

Fix GDI+ used for display method (got broken in some cleanup commits ago)
Remove some things meant to be removed in the last commit (fixes debug build)

src/BizHawk.Bizware.BizwareGL/IBlendState.cs

@@ -1,6 +0,0 @@
-namespace BizHawk.Bizware.BizwareGL
-{
-	public interface IBlendState
-	{
-	}
-}

src/BizHawk.Bizware.Graphics/GDIPlus/IGL_GDIPlus.cs

@@ -1,6 +1,7 @@
 using System;
 using System.IO;
 using System.Drawing;
+using System.Drawing.Drawing2D;
 using System.Drawing.Imaging;
 using System.Numerics;
 
@@ -39,12 +40,16 @@ namespace BizHawk.Bizware.Graphics
 
 		public void EnableBlending()
 		{
-			// TODO for real
+			var g = GetCurrentGraphics();
+			g.CompositingMode = CompositingMode.SourceOver;
+			g.CompositingQuality = CompositingQuality.Default;
 		}
 
 		public void DisableBlending()
 		{
-			// TODO for real
+			var g = GetCurrentGraphics();
+			g.CompositingMode = CompositingMode.SourceCopy;
+			g.CompositingQuality = CompositingQuality.HighSpeed;
 		}
 
 		public Pipeline CreatePipeline(VertexLayout vertexLayout, Shader vertexShader, Shader fragmentShader, bool required, string memo)

src/BizHawk.Bizware.Graphics/Renderers/GDIPlusGuiRenderer.cs

@@ -95,13 +95,15 @@ namespace BizHawk.Bizware.Graphics
 			CurrentImageAttributes.SetColorMatrix(colorMatrix,ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
 		}
 
-		private bool _enableBlending;
-
 		public void EnableBlending()
-			=> _enableBlending = true;
+		{
+			Owner.EnableBlending();
+		}
 
 		public void DisableBlending()
-			=> _enableBlending = false;
+		{ 
+			Owner.DisableBlending();
+		}
 
 		private MatrixStack _Projection, _Modelview;
 
@@ -133,7 +135,7 @@ namespace BizHawk.Bizware.Graphics
 		public void Begin(int width, int height)
 		{
 			Begin();
-			
+
 			Projection = Owner.CreateGuiProjectionMatrix(width, height);
 			Modelview = Owner.CreateGuiViewMatrix(width, height);
 		}
@@ -142,11 +144,12 @@ namespace BizHawk.Bizware.Graphics
 		{
 			// uhhmmm I want to throw an exception if its already active, but its annoying.
 			IsActive = true;
-			_enableBlending = false;
+			Owner.DisableBlending();
 
+			CurrentImageAttributes?.Dispose();
 			CurrentImageAttributes = new();
-			Modelview.Clear();
-			Projection.Clear();
+			Modelview?.Clear();
+			Projection?.Clear();
 		}
 
 		public void Flush()
@@ -187,8 +190,8 @@ namespace BizHawk.Bizware.Graphics
 			PointF[] destPoints =
 			{
 				new(x, y),
-				new(x+w, y),
-				new(x, y+h),
+				new(x + w, y),
+				new(x, y + h),
 			};
 
 			g.DrawImage(gtex.SDBitmap, destPoints, new(x0, y0, x1 - x0, y1 - y0), GraphicsUnit.Pixel, CurrentImageAttributes);
@@ -208,7 +211,7 @@ namespace BizHawk.Bizware.Graphics
 			DrawInternal(art, x, y, width, height);
 		}
 
-		private void PrepDraw(SDGraphics g, Texture2d tex)
+		private static void PrepDraw(SDGraphics g, Texture2d tex)
 		{
 			var tw = (GDIPlusTexture)tex.Opaque;
 
@@ -224,21 +227,6 @@ namespace BizHawk.Bizware.Graphics
 				TextureMagFilter.Nearest => InterpolationMode.NearestNeighbor,
 				_ => g.InterpolationMode
 			};
-
-			if (_enableBlending)
-			{
-				g.CompositingMode = CompositingMode.SourceOver;
-				g.CompositingQuality = CompositingQuality.Default; // ?
-			}
-			else
-			{
-				g.CompositingMode = CompositingMode.SourceCopy;
-				g.CompositingQuality = CompositingQuality.HighSpeed;
-
-				// WARNING : DO NOT USE COLOR MATRIX TO WIPE THE ALPHA
-				// ITS SOOOOOOOOOOOOOOOOOOOOOOOOOOOO SLOW
-				// instead, we added kind of hacky support for 24bpp images
-			}
 		}
 
 		private void SetupMatrix(SDGraphics g)

src/BizHawk.Bizware.Graphics/Renderers/GuiRenderer.cs

@@ -361,9 +361,6 @@ namespace BizHawk.Bizware.Graphics
 			pData[31] = CornerColors[3].W;
 
 			Owner.Draw(new(pData), 4);
-#if DEBUG
-			Debug.Assert(BlendStateSet);
-#endif
 		}
 
 		private void DrawSubrectInternal(Texture2d tex, float x, float y, float w, float h, float u0, float v0, float u1, float v1)
@@ -381,9 +378,6 @@ namespace BizHawk.Bizware.Graphics
 
 		// state cache
 		private Texture2d sTexture;
-#if DEBUG
-		private bool BlendStateSet;
-#endif
 
 		// shaders are hand-coded for each platform to make sure they stay as fast as possible
 

src/BizHawk.Client.Common/DisplayManager/Filters/Retro.cs

@@ -45,6 +45,12 @@ namespace BizHawk.Client.Common.Filters
 			Passes = preset.Passes.ToArray();
 			Errors = string.Empty;
 
+			if (owner.API is not ("OPENGL" or "D3D9"))
+			{
+				Errors = $"Unsupported API {owner.API}";
+				return;
+			}
+
 			// load up the shaders
 			var shaders = new RetroShader[preset.Passes.Count];
 			for (var i = 0; i < preset.Passes.Count; i++)