WIP: Add some complexity to LineCanvas when length is 0

Terminal.Gui/Core/Graphs/LineCanvas.cs

@@ -487,14 +487,6 @@ namespace Terminal.Gui.Graphs {
 
 			internal IntersectionDefinition Intersects (int x, int y)
 			{
-				if (IsDot ()) {
-					if (StartsAt (x, y)) {
-						return new IntersectionDefinition (Start, IntersectionType.Dot, this);
-					} else {
-						return null;
-					}
-				}
-
 				switch (Orientation) {
 				case Orientation.Horizontal: return IntersectsHorizontally (x, y);
 				case Orientation.Vertical: return IntersectsVertically (x, y);
@@ -552,7 +544,7 @@ namespace Terminal.Gui.Graphs {
 
 						return new IntersectionDefinition (
 							Start,
-							Length < 0 ? IntersectionType.StartUp : IntersectionType.StartDown,
+							GetTypeByLength(IntersectionType.StartUp, IntersectionType.PassOverVertical, IntersectionType.StartDown),
 							this
 							);
 
@@ -583,6 +575,15 @@ namespace Terminal.Gui.Graphs {
 				}
 			}
 
+			private IntersectionType GetTypeByLength (IntersectionType typeWhenNegative, IntersectionType typeWhenZero, IntersectionType typeWhenPositive)
+			{
+				if (Length == 0) {
+					return typeWhenZero;
+				} 
+
+				return Length < 0 ? typeWhenNegative : typeWhenPositive;
+			}
+
 			private bool EndsAt (int x, int y)
 			{
 				if (Orientation == Orientation.Horizontal) {

UnitTests/Core/LineCanvasTests.cs

@@ -311,7 +311,62 @@ namespace Terminal.Gui.CoreTests {
 ";
 			TestHelpers.AssertDriverContentsAre (looksLike, output);
 		}
+		[Fact, AutoInitShutdown]
+		public void TestLineCanvas_ClipArea_Intersections ()
+		{
+			// Draw at 1,1 within client area of View (i.e. leave a top and left margin of 1)
+			var v = GetCanvas (out var lc);
+			v.Width = 10;
+			v.Height = 1;
+			v.Bounds = new Rect (0, 0, 10, 1);
+
+			// ╔╡ Title ╞═════╗
+			// Add a short horiz line for ╔╡
+			lc.AddLine (new Point (0, 0), 1, Orientation.Horizontal, BorderStyle.Double);
+			//LHS line down
+			lc.AddLine (new Point (0, 0), 5, Orientation.Vertical, BorderStyle.Double);
+
+			//Vertical line before Title (must cover 3 squares so it results in a ╡ intersection
+			lc.AddLine (new Point (1, -1), 3, Orientation.Vertical, BorderStyle.Single);
+			//Vertical line after Title (must cover 3 squares so it results in a ╞ intersection
+			lc.AddLine (new Point (6, -1), 3, Orientation.Vertical, BorderStyle.Single);
+
+			// remainder of title
+			lc.AddLine (new Point (6, 0), 3, Orientation.Horizontal, BorderStyle.Double);
+			//RHS line down
+			lc.AddLine (new Point (9, 0), 5, Orientation.Vertical, BorderStyle.Double);
+
+			v.Redraw (v.Bounds);
+
+			string looksLike =
+		@"
+╔╡    ╞══╗
+";
+			TestHelpers.AssertDriverContentsAre (looksLike, output);
+		}
+
 
+		[Fact, AutoInitShutdown]
+		public void TestLineCanvas_CreateT_With_1Length_Plus_0Length ()
+		{
+			// Draw at 1,1 within client area of View (i.e. leave a top and left margin of 1)
+			var v = GetCanvas (out var lc);
+			v.Width = 10;
+			v.Height = 1;
+			v.Bounds = new Rect (0, 0, 10, 1);
+
+			// Create ═╡ with:
+			// A 1 width horizontal
+			lc.AddLine (new Point (0, 0), 1, Orientation.Horizontal, BorderStyle.Double);
+			// And a 0 length vertical 
+			lc.AddLine (new Point (1, 0), 0, Orientation.Vertical, BorderStyle.Single);
+
+			v.Redraw (v.Bounds);
+
+			string looksLike =
+		@"═╡";
+			TestHelpers.AssertDriverContentsAre (looksLike, output);
+		}
 
 		/// <summary>
 		/// Creates a new <see cref="View"/> into which a <see cref="LineCanvas"/> is rendered