From 88656e757c4d14a684a4965f5e288c5a1882cb1d Mon Sep 17 00:00:00 2001
From: Matthew Jimenez <matthew.jimenez@outlook.com>
Date: Wed, 27 Sep 2023 21:33:06 -0500
Subject: [PATCH] ULTIMA8: Adjust flat item rules based on more examples at map
 37

---
 engines/ultima/ultima8/world/sort_item.h      | 36 ++++++++++++++-----
 test/engines/ultima/ultima8/world/sort_item.h | 26 ++++++++++++++
 2 files changed, 54 insertions(+), 8 deletions(-)

diff --git a/engines/ultima/ultima8/world/sort_item.h b/engines/ultima/ultima8/world/sort_item.h
index 9ec31c22d2a..b0335ed5a94 100644
--- a/engines/ultima/ultima8/world/sort_item.h
+++ b/engines/ultima/ultima8/world/sort_item.h
@@ -498,22 +498,42 @@ inline bool SortItem::below(const SortItem &si2) const {
 	if (si1._roof != si2._roof)
 		return si1._roof > si2._roof;
 
-	// X-Flat gets drawn after when past center point
+	// X-Flat gets drawn after under specific conditions
 	bool xFlat1 = si1._xLeft == si1._x;
 	bool xFlat2 = si2._xLeft == si2._x;
 	if (xFlat1 != xFlat2 && si1._fixed == si2._fixed) {
-		int32 xCenter1 = (si1._xLeft + si1._x) / 2;
-		int32 xCenter2 = (si2._xLeft + si2._x) / 2;
-		return xFlat1 ? xCenter1 <= xCenter2 : xCenter1 < xCenter2;
+		if (xFlat1) {
+			if (si2._x - 32 > si2._xLeft) {
+				int32 xCenter2 = (si2._xLeft + si2._x) / 2;
+				return si1._x <= xCenter2;
+			}
+			return false;
+		} else {
+			if (si1._x - 32 > si1._xLeft) {
+				int32 xCenter1 = (si1._xLeft + si1._x) / 2;
+				return xCenter1 < si2._x;
+			}
+			return true;
+		}
 	}
 
-	// Y-Flat gets drawn after when past center point
+	// Y-Flat gets drawn after under specific conditions
 	bool yFlat1 = si1._yFar == si1._y;
 	bool yFlat2 = si2._yFar == si2._y;
 	if (yFlat1 != yFlat2 && si1._fixed == si2._fixed) {
-		int32 yCenter1 = (si1._yFar + si1._y) / 2;
-		int32 yCenter2 = (si2._yFar + si2._y) / 2;
-		return yFlat1 ? yCenter1 <= yCenter2 : yCenter1 < yCenter2;
+		if (yFlat1) {
+			if (si2._y - 32 > si2._yFar) {
+				int32 yCenter2 = (si2._yFar + si2._y) / 2;
+				return si1._y <= yCenter2;
+			}
+			return false;
+		} else {
+			if (si1._y - 32 > si1._yFar) {
+				int32 yCenter1 = (si1._yFar + si1._y) / 2;
+				return yCenter1 < si2._y;
+			}
+			return true;
+		}
 	}
 
 	// Partial in X + Y front
diff --git a/test/engines/ultima/ultima8/world/sort_item.h b/test/engines/ultima/ultima8/world/sort_item.h
index 9f3b370318d..b37c52f51d1 100644
--- a/test/engines/ultima/ultima8/world/sort_item.h
+++ b/test/engines/ultima/ultima8/world/sort_item.h
@@ -319,6 +319,30 @@ class U8SortItemTestSuite : public CxxTest::TestSuite {
 		TS_ASSERT(!si2.below(si1));
 	}
 
+	/**
+	 * Overlapping x-flat vs non-flat wall with x-flat far inside wall
+	 * Test case for rendering issue at MainActor::teleport 37 17619 17767 104
+	 * Tapestry should draw after wall again
+	 */
+	void test_x_flat_vs_thin_wall_sort() {
+		Ultima::Ultima8::SortItem si1;
+		Ultima::Ultima8::SortItem si2;
+
+		Ultima::Ultima8::Box b1(17439, 17535, 104, 32, 128, 40);
+		si1.setBoxBounds(b1, 0, 0);
+		si1._solid = true;
+		si1._occl = true;
+		si1._land = true;
+		si1._fixed = true;
+
+		Ultima::Ultima8::Box b2(17410, 17502, 96, 0, 96, 40);
+		si2.setBoxBounds(b2, 0, 0);
+		si2._fixed = true;
+
+		TS_ASSERT(si1.below(si2));
+		TS_ASSERT(!si2.below(si1));
+	}
+
 	/**
 	 * Overlapping x-flat vs non-flat items but the flat item was misplaced
 	 * Test case for rendering issue at MainActor::teleport 41 19411 15787 48
@@ -406,9 +430,11 @@ class U8SortItemTestSuite : public CxxTest::TestSuite {
 		si1._trans = true;
 		si1._solid = true;
 		si1._land = true;
+		si1._fixed = true;
 
 		Ultima::Ultima8::Box b2(20543, 9855, 48, 96, 0, 16);
 		si2.setBoxBounds(b2, 0, 0);
+		si2._fixed = true;
 
 		TS_ASSERT(si1.overlap(si2));
 		TS_ASSERT(si2.overlap(si1));