From 33a899d6dd02618aca8c4d13c5f4040f3e5c2ee2 Mon Sep 17 00:00:00 2001
From: Zack Middleton <zack@cloemail.com>
Date: Sat, 15 Sep 2018 11:53:21 -0500
Subject: [PATCH] Fix predicting entity origin on rotating mover

Based on G_TryPushingEntity() in code/game/g_mover.c.
---
 code/cgame/cg_ents.c | 50 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/code/cgame/cg_ents.c b/code/cgame/cg_ents.c
index 7629f0b8..ec8b02ff 100644
--- a/code/cgame/cg_ents.c
+++ b/code/cgame/cg_ents.c
@@ -664,6 +664,44 @@ static void CG_Portal( centity_t *cent ) {
 }
 
 
+/*
+================
+CG_CreateRotationMatrix
+================
+*/
+void CG_CreateRotationMatrix(vec3_t angles, vec3_t matrix[3]) {
+	AngleVectors(angles, matrix[0], matrix[1], matrix[2]);
+	VectorInverse(matrix[1]);
+}
+
+/*
+================
+CG_TransposeMatrix
+================
+*/
+void CG_TransposeMatrix(vec3_t matrix[3], vec3_t transpose[3]) {
+	int i, j;
+	for (i = 0; i < 3; i++) {
+		for (j = 0; j < 3; j++) {
+			transpose[i][j] = matrix[j][i];
+		}
+	}
+}
+
+/*
+================
+CG_RotatePoint
+================
+*/
+void CG_RotatePoint(vec3_t point, vec3_t matrix[3]) {
+	vec3_t tvec;
+
+	VectorCopy(point, tvec);
+	point[0] = DotProduct(matrix[0], tvec);
+	point[1] = DotProduct(matrix[1], tvec);
+	point[2] = DotProduct(matrix[2], tvec);
+}
+
 /*
 =========================
 CG_AdjustPositionForMover
@@ -675,6 +713,8 @@ void CG_AdjustPositionForMover(const vec3_t in, int moverNum, int fromTime, int
 	centity_t	*cent;
 	vec3_t	oldOrigin, origin, deltaOrigin;
 	vec3_t	oldAngles, angles, deltaAngles;
+	vec3_t	matrix[3], transpose[3];
+	vec3_t	org, org2, move2;
 
 	if ( moverNum <= 0 || moverNum >= ENTITYNUM_MAX_NORMAL ) {
 		VectorCopy( in, out );
@@ -698,9 +738,17 @@ void CG_AdjustPositionForMover(const vec3_t in, int moverNum, int fromTime, int
 	VectorSubtract( origin, oldOrigin, deltaOrigin );
 	VectorSubtract( angles, oldAngles, deltaAngles );
 
+	// origin change when on a rotating object
+	CG_CreateRotationMatrix( deltaAngles, transpose );
+	CG_TransposeMatrix( transpose, matrix );
+	VectorSubtract( in, oldOrigin, org );
+	VectorCopy( org, org2 );
+	CG_RotatePoint( org2, matrix );
+	VectorSubtract( org2, org, move2 );
+	VectorAdd( deltaOrigin, move2, deltaOrigin );
+
 	VectorAdd( in, deltaOrigin, out );
 	VectorAdd( angles_in, deltaAngles, angles_out );
-	// FIXME: origin change when on a rotating object
 }