Feature: [NewGRF] Maximum curve speed modifier for rail vehicles (#9346)

1 files changed, 11 insertions, 4 deletions

diff --git a/src/newgrf_engine.cpp b/src/newgrf_engine.cpp
index fa26f7b68..e57410224 100644
--- a/src/newgrf_engine.cpp
+++ b/src/newgrf_engine.cpp
@@ -1177,16 +1177,23 @@ uint16 GetVehicleCallbackParent(CallbackID callback, uint32 param1, uint32 param
 
 
 /* Callback 36 handlers */
-uint GetVehicleProperty(const Vehicle *v, PropertyID property, uint orig_value)
+int GetVehicleProperty(const Vehicle *v, PropertyID property, int orig_value, bool is_signed)
 {
-	return GetEngineProperty(v->engine_type, property, orig_value, v);
+	return GetEngineProperty(v->engine_type, property, orig_value, v, is_signed);
 }
 
 
-uint GetEngineProperty(EngineID engine, PropertyID property, uint orig_value, const Vehicle *v)
+int GetEngineProperty(EngineID engine, PropertyID property, int orig_value, const Vehicle *v, bool is_signed)
 {
 	uint16 callback = GetVehicleCallback(CBID_VEHICLE_MODIFY_PROPERTY, property, 0, engine, v);
-	if (callback != CALLBACK_FAILED) return callback;
+	if (callback != CALLBACK_FAILED) {
+		if (is_signed) {
+			/* Sign extend 15 bit integer */
+			return static_cast<int16>(callback << 1) >> 1;
+		} else {
+			return callback;
+		}
+	}
 
 	return orig_value;
 }