From ce413ec4a6ddf1528ccd655bb900c0952123e1e7 Mon Sep 17 00:00:00 2001
From: staphen <staphen@gmail.com>
Date: Tue, 6 Dec 2022 22:53:38 -0500
Subject: [PATCH] Round to the nearest integer when computing missile
 coordinates

---
 Source/engine/displacement.hpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Source/engine/displacement.hpp b/Source/engine/displacement.hpp
index c30bf4c9c..4d1bef384 100644
--- a/Source/engine/displacement.hpp
+++ b/Source/engine/displacement.hpp
@@ -155,11 +155,16 @@ struct DisplacementOf {
 
 	/**
 	 * @brief Missiles flip the axes for some reason -_-
-	 * @return negated world displacement, for use with missile movement routines.
+	 * @return negated and rounded world displacement, for use with missile movement routines.
 	 */
 	constexpr DisplacementOf<DeltaT> screenToMissile() const
 	{
-		return -screenToWorld();
+		static_assert(std::is_signed<DeltaT>::value, "DeltaT must be signed for transformations involving a rotation");
+		DeltaT xNumerator = 2 * deltaY + deltaX;
+		DeltaT yNumerator = 2 * deltaY - deltaX;
+		DeltaT xOffset = (xNumerator >= 0) ? 32 : -32;
+		DeltaT yOffset = (yNumerator >= 0) ? 32 : -32;
+		return { (xNumerator + xOffset) / 64, (yNumerator + yOffset) / 64 };
 	}
 
 	constexpr DisplacementOf<DeltaT> screenToLight() const