Use custom sprite sorting rules for vehicles diagonally under bridges

Extend bb sprite south for comparisons, but only for vehicles underneath
This is to avoid creating sprite sorting problems for vehicles
on top of the bridge

Adjust ParentSpriteToDraw struct

src/tunnelbridge_cmd.cpp

@@ -2495,7 +2495,12 @@ void DrawBridgeMiddle(const TileInfo *ti)
 	int z = bridge_z - BRIDGE_Z_START;
 
 	/* Add a bounding box that separates the bridge from things below it. */
-	AddSortableSpriteToDraw(SPR_EMPTY_BOUNDING_BOX, PAL_NONE, x, y, 16, 16, 1, bridge_z - TILE_HEIGHT + BB_Z_SEPARATOR);
+	ViewportSortableSpriteSpecialFlags special_flags = VSSF_NONE;
+	if (IsPlainRailTile(ti->tile) && (GetTrackBits(ti->tile) & (TRACK_BIT_LEFT | TRACK_BIT_RIGHT | TRACK_BIT_LOWER)) != 0) {
+		/* Problematic diagonal rail track is underneath this bridge */
+		special_flags = VSSSF_SORT_SPECIAL | VSSSF_SORT_SORT_BRIDGE_BB;
+	}
+	AddSortableSpriteToDraw(SPR_EMPTY_BOUNDING_BOX, PAL_NONE, x, y, 16, 16, 1, bridge_z - TILE_HEIGHT + BB_Z_SEPARATOR, false, 0, 0, 0, nullptr, special_flags);
 
 	/* Draw Trambits as SpriteCombine */
 	if (transport_type == TRANSPORT_ROAD || transport_type == TRANSPORT_RAIL) StartSpriteCombine();

src/vehicle.cpp

@@ -1862,12 +1862,14 @@ static void DoDrawVehicle(const Vehicle *v)
 		}
 	}
 
+	ViewportSortableSpriteSpecialFlags special_flags = IsDiagonalDirection(v->direction) ? VSSF_NONE : VSSSF_SORT_SPECIAL | VSSSF_SORT_DIAG_VEH;
+
 	StartSpriteCombine();
 	for (uint i = 0; i < v->sprite_seq.count; ++i) {
 		PaletteID pal2 = v->sprite_seq.seq[i].pal;
 		if (!pal2 || (v->vehstatus & VS_CRASHED)) pal2 = pal;
 		AddSortableSpriteToDraw(v->sprite_seq.seq[i].sprite, pal2, v->x_pos + v->x_offs, v->y_pos + v->y_offs,
-			v->x_extent, v->y_extent, v->z_extent, v->z_pos, shadowed, v->x_bb_offs, v->y_bb_offs);
+			v->x_extent, v->y_extent, v->z_extent, v->z_pos, shadowed, v->x_bb_offs, v->y_bb_offs, 0, nullptr, special_flags);
 	}
 	EndSpriteCombine();
 }

src/viewport.cpp

@@ -287,6 +287,7 @@ struct ViewportDrawerDynamic {
 	TileSpriteToDrawVector tile_sprites_to_draw;
 	ParentSpriteToDrawVector parent_sprites_to_draw;
 	std::vector<ViewportProcessParentSpritesData> parent_sprite_sets;
+	ParentSpriteToDrawSubSpriteHolder parent_sprite_subsprites;
 	ChildScreenSpriteToDrawVector child_screen_sprites_to_draw;
 	btree::btree_map<TileIndex, TileIndex, BridgeSetXComparator> bridge_to_map_x;
 	btree::btree_map<TileIndex, TileIndex, BridgeSetYComparator> bridge_to_map_y;
@@ -1231,8 +1232,9 @@ static void AddCombinedSprite(SpriteID image, PaletteID pal, int x, int y, int z
  * @param bb_offset_y bounding box extent towards negative Y (world),
  * @param bb_offset_z bounding box extent towards negative Z (world)
  * @param sub Only draw a part of the sprite.
+ * @param special_flags Special flags (special sorting, etc).
  */
-void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w, int h, int dz, int z, bool transparent, int bb_offset_x, int bb_offset_y, int bb_offset_z, const SubSprite *sub)
+void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w, int h, int dz, int z, bool transparent, int bb_offset_x, int bb_offset_y, int bb_offset_z, const SubSprite *sub, ViewportSortableSpriteSpecialFlags special_flags)
 {
 	int32_t left, right, top, bottom;
 
@@ -1298,7 +1300,9 @@ void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w,
 
 	ps.image = image;
 	ps.pal = pal;
-	ps.sub = sub;
+	_vdd->parent_sprite_subsprites.Set(&ps, sub);
+	ps.special_flags = special_flags;
+
 	ps.xmin = x + bb_offset_x;
 	ps.xmax = x + std::max(bb_offset_x, w) - 1;
 
@@ -1327,6 +1331,11 @@ void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w,
 	}
 }
 
+void SetLastSortableSpriteToDrawSpecialFlags(ViewportSortableSpriteSpecialFlags flags)
+{
+	_vdd->parent_sprites_to_draw.back().special_flags = flags;
+}
+
 /**
  * Starts a block of sprites, which are "combined" into a single bounding box.
  *
@@ -2143,11 +2152,75 @@ static bool ViewportSortParentSpritesChecker()
 	return true;
 }
 
+static void ViewportSortParentSpritesSingleComparison(ParentSpriteToDraw *ps, ParentSpriteToDraw *ps2, ParentSpriteToDraw *ps_to_move, ParentSpriteToDraw **psd, ParentSpriteToDraw **psd2)
+{
+	/* Decide which comparator to use, based on whether the bounding
+	 * boxes overlap
+	 */
+	if (ps->xmax >= ps2->xmin && ps->xmin <= ps2->xmax && // overlap in X?
+			ps->ymax >= ps2->ymin && ps->ymin <= ps2->ymax && // overlap in Y?
+			ps->zmax >= ps2->zmin && ps->zmin <= ps2->zmax) { // overlap in Z?
+		/* Use X+Y+Z as the sorting order, so sprites closer to the bottom of
+		 * the screen and with higher Z elevation, are drawn in front.
+		 * Here X,Y,Z are the coordinates of the "center of mass" of the sprite,
+		 * i.e. X=(left+right)/2, etc.
+		 * However, since we only care about order, don't actually divide / 2
+		 */
+		if (ps->xmin + ps->xmax + ps->ymin + ps->ymax + ps->zmin + ps->zmax <=
+				ps2->xmin + ps2->xmax + ps2->ymin + ps2->ymax + ps2->zmin + ps2->zmax) {
+			return;
+		}
+	} else {
+		/* We only change the order, if it is definite.
+		 * I.e. every single order of X, Y, Z says ps2 is behind ps or they overlap.
+		 * That is: If one partial order says ps behind ps2, do not change the order.
+		 */
+		if (ps->xmax < ps2->xmin ||
+				ps->ymax < ps2->ymin ||
+				ps->zmax < ps2->zmin) {
+			return;
+		}
+	}
+
+	/* Move ps_to_move (ps2) in front of ps */
+	ParentSpriteToDraw *temp = ps_to_move;
+	for (auto psd3 = psd2; psd3 > psd; psd3--) {
+		*psd3 = *(psd3 - 1);
+	}
+	*psd = temp;
+}
+
+bool ViewportSortParentSpritesSpecial(ParentSpriteToDraw *ps, ParentSpriteToDraw *ps2, ParentSpriteToDraw **psd, ParentSpriteToDraw **psd2)
+{
+	ParentSpriteToDraw temp;
+
+	auto is_bridge_diag_veh_comparison = [&](ParentSpriteToDraw *a, ParentSpriteToDraw *b) -> bool {
+		if ((a->special_flags & VSSSF_SORT_SPECIAL_TYPE_MASK) == VSSSF_SORT_SORT_BRIDGE_BB && (b->special_flags & VSSSF_SORT_SPECIAL_TYPE_MASK) == VSSSF_SORT_DIAG_VEH && a->zmin > b->zmax) {
+			temp = *a;
+			temp.xmax += 4;
+			temp.ymax += 4;
+			return true;
+		}
+		return false;
+	};
+
+	if (is_bridge_diag_veh_comparison(ps, ps2)) {
+		ViewportSortParentSpritesSingleComparison(&temp, ps2, ps2, psd, psd2);
+		return true;
+	}
+	if (is_bridge_diag_veh_comparison(ps2, ps)) {
+		ViewportSortParentSpritesSingleComparison(ps, &temp, ps2, psd, psd2);
+		return true;
+	}
+
+	return false;
+}
+
 /** Sort parent sprites pointer array */
 static void ViewportSortParentSprites(ParentSpriteToSortVector *psdv)
 {
-	auto psdvend = psdv->end();
-	auto psd = psdv->begin();
+	ParentSpriteToDraw ** const psdvend = psdv->data() + psdv->size();
+	ParentSpriteToDraw **psd = psdv->data();
 	while (psd != psdvend) {
 		ParentSpriteToDraw *ps = *psd;
 
@@ -2157,46 +2230,18 @@ static void ViewportSortParentSprites(ParentSpriteToSortVector *psdv)
 		}
 
 		ps->SetComparisonDone(true);
+		const bool is_special = (ps->special_flags & VSSSF_SORT_SPECIAL) != 0;
 
 		for (auto psd2 = psd + 1; psd2 != psdvend; psd2++) {
 			ParentSpriteToDraw *ps2 = *psd2;
 
 			if (ps2->IsComparisonDone()) continue;
 
-			/* Decide which comparator to use, based on whether the bounding
-			 * boxes overlap
-			 */
-			if (ps->xmax >= ps2->xmin && ps->xmin <= ps2->xmax && // overlap in X?
-					ps->ymax >= ps2->ymin && ps->ymin <= ps2->ymax && // overlap in Y?
-					ps->zmax >= ps2->zmin && ps->zmin <= ps2->zmax) { // overlap in Z?
-				/* Use X+Y+Z as the sorting order, so sprites closer to the bottom of
-				 * the screen and with higher Z elevation, are drawn in front.
-				 * Here X,Y,Z are the coordinates of the "center of mass" of the sprite,
-				 * i.e. X=(left+right)/2, etc.
-				 * However, since we only care about order, don't actually divide / 2
-				 */
-				if (ps->xmin + ps->xmax + ps->ymin + ps->ymax + ps->zmin + ps->zmax <=
-						ps2->xmin + ps2->xmax + ps2->ymin + ps2->ymax + ps2->zmin + ps2->zmax) {
-					continue;
-				}
-			} else {
-				/* We only change the order, if it is definite.
-				 * I.e. every single order of X, Y, Z says ps2 is behind ps or they overlap.
-				 * That is: If one partial order says ps behind ps2, do not change the order.
-				 */
-				if (ps->xmax < ps2->xmin ||
-						ps->ymax < ps2->ymin ||
-						ps->zmax < ps2->zmin) {
-					continue;
-				}
+			if (is_special && (ps2->special_flags & VSSSF_SORT_SPECIAL) != 0) {
+				if (ViewportSortParentSpritesSpecial(ps, ps2, psd, psd2)) continue;
 			}
 
-			/* Move ps2 in front of ps */
-			ParentSpriteToDraw *temp = ps2;
-			for (auto psd3 = psd2; psd3 > psd; psd3--) {
-				*psd3 = *(psd3 - 1);
-			}
-			*psd = temp;
+			ViewportSortParentSpritesSingleComparison(ps, ps2, ps2, psd, psd2);
 		}
 	}
 }
@@ -2204,7 +2249,7 @@ static void ViewportSortParentSprites(ParentSpriteToSortVector *psdv)
 static void ViewportDrawParentSprites(const ViewportDrawerDynamic *vdd, const DrawPixelInfo *dpi, const ParentSpriteToSortVector *psd, const ChildScreenSpriteToDrawVector *csstdv)
 {
 	for (const ParentSpriteToDraw *ps : *psd) {
-		if (ps->image != SPR_EMPTY_BOUNDING_BOX) DrawSpriteViewport(vdd->sprite_data, dpi, ps->image, ps->pal, ps->x, ps->y, ps->sub);
+		if (ps->image != SPR_EMPTY_BOUNDING_BOX) DrawSpriteViewport(vdd->sprite_data, dpi, ps->image, ps->pal, ps->x, ps->y, vdd->parent_sprite_subsprites.Get(ps));
 
 		int child_idx = ps->first_child;
 		while (child_idx >= 0) {
@@ -4140,6 +4185,7 @@ static void ViewportDoDrawPhase3(Viewport *vp)
 	_vdd->tile_sprites_to_draw.clear();
 	_vdd->parent_sprites_to_draw.clear();
 	_vdd->parent_sprite_sets.clear();
+	_vdd->parent_sprite_subsprites.Clear();
 	_vdd->child_screen_sprites_to_draw.clear();
 	_vdd->sprite_data.Clear();
 

src/viewport_func.h

@@ -72,9 +72,18 @@ inline void MaxZoomInOut(ZoomStateChange how, Window *w)
 
 void OffsetGroundSprite(int x, int y);
 
+enum ViewportSortableSpriteSpecialFlags : uint8_t {
+	VSSF_NONE                      =    0,
+	VSSSF_SORT_SPECIAL             = 0x80, ///< When sorting sprites, if both sprites have this set, special sorting rules apply
+	VSSSF_SORT_SPECIAL_TYPE_MASK   =    1, ///< Mask to use for getting the special type
+	VSSSF_SORT_DIAG_VEH            =    0, ///< This is a vehicle moving diagonally with respect to the tile axes
+	VSSSF_SORT_SORT_BRIDGE_BB      =    1, ///< This is a bridge BB helper sprite
+};
+DECLARE_ENUM_AS_BIT_SET(ViewportSortableSpriteSpecialFlags);
+
 void DrawGroundSprite(SpriteID image, PaletteID pal, const SubSprite *sub = nullptr, int extra_offs_x = 0, int extra_offs_y = 0);
 void DrawGroundSpriteAt(SpriteID image, PaletteID pal, int32_t x, int32_t y, int z, const SubSprite *sub = nullptr, int extra_offs_x = 0, int extra_offs_y = 0);
-void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w, int h, int dz, int z, bool transparent = false, int bb_offset_x = 0, int bb_offset_y = 0, int bb_offset_z = 0, const SubSprite *sub = nullptr);
+void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w, int h, int dz, int z, bool transparent = false, int bb_offset_x = 0, int bb_offset_y = 0, int bb_offset_z = 0, const SubSprite *sub = nullptr, ViewportSortableSpriteSpecialFlags special_flags = VSSF_NONE);
 void AddChildSpriteScreen(SpriteID image, PaletteID pal, int x, int y, bool transparent = false, const SubSprite *sub = nullptr, bool scale = true, ChildScreenSpritePositionMode position_mode = ChildScreenSpritePositionMode::Relative);
 void ViewportAddString(ViewportDrawerDynamic *vdd, const DrawPixelInfo *dpi, ZoomLevel small_from, const ViewportSign *sign, StringID string_normal, StringID string_small, StringID string_small_shadow, uint64_t params_1, uint64_t params_2 = 0, Colours colour = INVALID_COLOUR);
 

src/viewport_sprite_sorter.h

@@ -34,7 +34,14 @@ struct __attribute__ ((aligned (16))) ParentSpriteToDraw {
 
 	SpriteID image;                 ///< sprite to draw
 	PaletteID pal;                  ///< palette to use
-	const SubSprite *sub;           ///< only draw a rectangular part of the sprite
+#ifdef POINTER_IS_64BIT
+	int32_t sub_idx;                ///< only draw a rectangular part of the sprite (store the actual pointer elsewhere to save space in this struct)
+#else
+	const SubSprite *sub_ptr;       ///< only draw a rectangular part of the sprite
+#endif
+	uint8_t special_flags;          ///< special flags
+
+	/* 3 bytes spare! */
 
 	int32_t left;                   ///< minimal screen X coordinate of sprite (= x + sprite->x_offs), reference point for child sprites
 	int32_t top;                    ///< minimal screen Y coordinate of sprite (= y + sprite->y_offs), reference point for child sprites
@@ -51,11 +58,45 @@ static_assert(sizeof(ParentSpriteToDraw) <= 64);
 
 typedef std::vector<ParentSpriteToDraw*> ParentSpriteToSortVector;
 
+#ifdef POINTER_IS_64BIT
+struct ParentSpriteToDrawSubSpriteHolder {
+	std::vector<const SubSprite *> subsprites;
+
+	const SubSprite *Get(const ParentSpriteToDraw *ps) const
+	{
+		return ps->sub_idx >= 0 ? this->subsprites[ps->sub_idx] : nullptr;
+	}
+
+	void Set(ParentSpriteToDraw *ps, const SubSprite *sub)
+	{
+		if (sub == nullptr) {
+			ps->sub_idx = -1;
+		} else {
+			ps->sub_idx = (int32_t)this->subsprites.size();
+			this->subsprites.push_back(sub);
+		}
+	}
+
+	void Clear()
+	{
+		this->subsprites.clear();
+	}
+};
+#else
+struct ParentSpriteToDrawSubSpriteHolder {
+	const SubSprite *Get(const ParentSpriteToDraw *ps) const { return ps->sub_ptr; }
+	void Set(ParentSpriteToDraw *ps, const SubSprite *sub) { ps->sub_ptr = sub; }
+	void Clear() {}
+};
+#endif
+
 /** Type for method for checking whether a viewport sprite sorter exists. */
 typedef bool (*VpSorterChecker)();
 /** Type for the actual viewport sprite sorter. */
 typedef void (*VpSpriteSorter)(ParentSpriteToSortVector *psd);
 
+bool ViewportSortParentSpritesSpecial(ParentSpriteToDraw *ps, ParentSpriteToDraw *ps2, ParentSpriteToDraw **psd, ParentSpriteToDraw **psd2);
+
 #ifdef WITH_SSE
 bool ViewportSortParentSpritesSSE41Checker();
 void ViewportSortParentSpritesSSE41(ParentSpriteToSortVector *psdv);

src/viewport_sprite_sorter_sse4.cpp

@@ -13,6 +13,7 @@
 #include "cpu.h"
 #include "smmintrin.h"
 #include "viewport_sprite_sorter.h"
+#include "viewport_func.h"
 
 #include "safeguards.h"
 
@@ -28,8 +29,8 @@ GNU_TARGET("sse4.1")
 void ViewportSortParentSpritesSSE41(ParentSpriteToSortVector *psdv)
 {
 	const __m128i mask_ptest = _mm_setr_epi8(-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,  0,  0,  0,  0);
-	auto const psdvend = psdv->end();
-	auto psd = psdv->begin();
+	ParentSpriteToDraw ** const psdvend = psdv->data() + psdv->size();
+	ParentSpriteToDraw **psd = psdv->data();
 	while (psd != psdvend) {
 		ParentSpriteToDraw * const ps = *psd;
 
@@ -39,12 +40,17 @@ void ViewportSortParentSpritesSSE41(ParentSpriteToSortVector *psdv)
 		}
 
 		ps->SetComparisonDone(true);
+		const bool is_special = (ps->special_flags & VSSSF_SORT_SPECIAL) != 0;
 
 		for (auto psd2 = psd + 1; psd2 != psdvend; psd2++) {
 			ParentSpriteToDraw * const ps2 = *psd2;
 
 			if (ps2->IsComparisonDone()) continue;
 
+			if (is_special && (ps2->special_flags & VSSSF_SORT_SPECIAL) != 0) {
+				if (ViewportSortParentSpritesSpecial(ps, ps2, psd, psd2)) continue;
+			}
+
 			/*
 			 * Decide which comparator to use, based on whether the bounding boxes overlap
 			 *