Drawing slope handles works correctly now

Source/Core/Rendering/VisualSlopeHandle.cs

@@ -56,13 +56,13 @@ namespace CodeImp.DoomBuilder.Rendering
 		// (when resized or display adapter was changed)
 		public void ReloadResource()
 		{
-			WorldVertex v0 = new WorldVertex(0.0f, 0.0f, 0.5f);
-			WorldVertex v1 = new WorldVertex(1.0f, 0.0f, 0.5f);
-			WorldVertex v2 = new WorldVertex(1.0f, 8.0f, 0.5f);
-			WorldVertex v3 = new WorldVertex(0.0f, 8.0f, 0.5f);
+			WorldVertex v0 = new WorldVertex(0.0f, -8.0f, 0.5f);
+			WorldVertex v1 = new WorldVertex(0.0f, 0.0f, 0.5f);
+			WorldVertex v2 = new WorldVertex(1.0f, 0.0f, 0.5f);
+			WorldVertex v3 = new WorldVertex(1.0f, -8.0f, 0.5f);
 
-			v0.c = v1.c = PixelColor.INT_WHITE;
-			v2.c = v3.c = PixelColor.INT_WHITE_NO_ALPHA;
+			v1.c = v2.c = PixelColor.INT_WHITE;
+			v0.c = v3.c = PixelColor.INT_WHITE_NO_ALPHA;
 
 			WorldVertex[] vertices = new[]
 			{

Source/Core/VisualModes/VisualSlope.cs

@@ -28,7 +28,6 @@ namespace CodeImp.DoomBuilder.VisualModes
 
 		private Matrix position;
 
-
 		#endregion
 
 		#region ================== Properties
@@ -103,12 +102,14 @@ namespace CodeImp.DoomBuilder.VisualModes
 
 		public void SetPosition(Line2D line, Plane plane)
 		{
+			Line3D line3d = new Line3D(new Vector3D(line.v1, plane.GetZ(line.v1)), new Vector3D(line.v2, plane.GetZ(line.v2)));
+
 			// This vector is perpendicular to the line, with a 90° angle between it and the plane normal
-			Vector3D perpendicularvector = Vector3D.CrossProduct(line.GetDelta().GetNormal(), plane.Normal);
+			Vector3D perpendicularvector = Vector3D.CrossProduct(line3d.GetDelta().GetNormal(), plane.Normal) * (-1);
 
 			// This vector is on the plane, with a 90° angle to the perpendicular vector (so effectively
 			// it's on the line, but in 3D
-			Vector3D linevector = Vector3D.CrossProduct(plane.Normal, perpendicularvector);
+			Vector3D linevector = Vector3D.CrossProduct(plane.Normal, perpendicularvector) * (-1);
 
 			Matrix m = Matrix.Null;