Codechange: consider vehicle co-ordinates when identifying viewport candidate as using only the hash generates false positives

2 files changed, 19 insertions, 13 deletions

diff --git a/src/vehicle.cpp b/src/vehicle.cpp
index 89cabe20d..e35842118 100644
--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -1124,11 +1124,15 @@ void ViewportAddVehicles(DrawPixelInfo *dpi)
 	const int t = dpi->top;
 	const int b = dpi->top + dpi->height;
 
+	/* Border size of MAX_VEHICLE_PIXEL_xy */
+	const int xb = MAX_VEHICLE_PIXEL_X * ZOOM_LVL_BASE;
+	const int yb = MAX_VEHICLE_PIXEL_Y * ZOOM_LVL_BASE;
+
 	/* The hash area to scan */
 	int xl, xu, yl, yu;
 
-	if (dpi->width + (MAX_VEHICLE_PIXEL_X * ZOOM_LVL_BASE) < GEN_HASHX_SIZE) {
-		xl = GEN_HASHX(l - MAX_VEHICLE_PIXEL_X * ZOOM_LVL_BASE);
+	if (dpi->width + xb < GEN_HASHX_SIZE) {
+		xl = GEN_HASHX(l - xb);
 		xu = GEN_HASHX(r);
 	} else {
 		/* scan whole hash row */
@@ -1136,8 +1140,8 @@ void ViewportAddVehicles(DrawPixelInfo *dpi)
 		xu = GEN_HASHX_MASK;
 	}
 
-	if (dpi->height + (MAX_VEHICLE_PIXEL_Y * ZOOM_LVL_BASE) < GEN_HASHY_SIZE) {
-		yl = GEN_HASHY(t - MAX_VEHICLE_PIXEL_Y * ZOOM_LVL_BASE);
+	if (dpi->height + yb < GEN_HASHY_SIZE) {
+		yl = GEN_HASHY(t - yb);
 		yu = GEN_HASHY(b);
 	} else {
 		/* scan whole column */
@@ -1158,9 +1162,14 @@ void ViewportAddVehicles(DrawPixelInfo *dpi)
 						b >= v->coord.top) {
 					DoDrawVehicle(v);
 				}
-				else {
+				else if (l <= v->coord.right + xb &&
+					t <= v->coord.bottom + yb &&
+					r >= v->coord.left - xb &&
+					b >= v->coord.top - yb)
+				{
 					/*
 					 * Indicate that this vehicle was considered for rendering in a viewport,
+					 * is within the bounds where a sprite could be valid for rendering
 					 * and we therefore need to update sprites more frequently in case a callback
 					 * will change the bounding box to one which will cause the sprite to be
 					 * displayed.
@@ -1168,9 +1177,6 @@ void ViewportAddVehicles(DrawPixelInfo *dpi)
 					 * This reduces the chances of flicker when sprites enter the screen, if they
 					 * are part of a newgrf vehicle set which changes bounding boxes within a
 					 * single vehicle direction.
-					 *
-					 * TODO: this will consider too many false positives, use the bounding box
-					 * information or something which better narrows down the candidates.
 					 */
 					v->sprite_cache.is_viewport_candidate = true;
 				}
diff --git a/src/vehicle_base.h b/src/vehicle_base.h
index d6a02cc0c..24facfb3e 100644
--- a/src/vehicle_base.h
+++ b/src/vehicle_base.h
@@ -186,10 +186,10 @@ struct VehicleSpriteSeq {
  * or calculating the viewport.
  */
 struct MutableSpriteCache {
-	Direction last_direction;                 ///< Last direction we obtained sprites for
-	mutable bool is_viewport_candidate;       ///< The vehicle has been in the hash for a shown viewport recently
-	mutable bool sprite_has_viewport_changes; ///< There have been viewport changes since the sprite was last updated
-	mutable VehicleSpriteSeq sprite_seq;      ///< Vehicle appearance.
+	Direction last_direction;         ///< Last direction we obtained sprites for
+	bool is_viewport_candidate;       ///< The vehicle has been in the hash for a shown viewport recently
+	bool sprite_has_viewport_changes; ///< There have been viewport changes since the sprite was last updated
+	VehicleSpriteSeq sprite_seq;      ///< Vehicle appearance.
 };
 
 /** A vehicle pool for a little over 1 million vehicles. */
@@ -337,7 +337,7 @@ public:
 	NewGRFCache grf_cache;              ///< Cache of often used calculated NewGRF values
 	VehicleCache vcache;                ///< Cache of often used vehicle values.
 
-	MutableSpriteCache sprite_cache;    ///< Cache of sprites and values related to recalculating them, see #MutableSpriteCache
+	mutable MutableSpriteCache sprite_cache; ///< Cache of sprites and values related to recalculating them, see #MutableSpriteCache
 
 	Vehicle(VehicleType type = VEH_INVALID);