display3d.cpp: don't use heap allocation for buildBlueprint()

This function is called for every frame, so to avoid
constantly inserting/deleting to/from `GlobalStructContainer()`,
just construct the pseudo-structure for the blueprint on stack.

This seems to work well enough, meaning that `mouseTarget()`,
which, in turn, calls `getTileBlueprintStructure()`,
doesn't do anything horribly wrong.

Signed-off-by: Pavel Solodovnikov <pavel.al.solodovnikov@gmail.com>

src/display3d.cpp

@@ -352,19 +352,17 @@ struct Blueprint
 	{
 		return compare(b) == 0;
 	}
-	STRUCTURE *buildBlueprint() const  ///< Must delete after use.
+	optional<STRUCTURE> buildBlueprint() const
 	{
 		return ::buildBlueprint(stats, pos, dir, index, state, player);
 	}
 	void renderBlueprint(const glm::mat4 &viewMatrix, const glm::mat4 &perspectiveViewMatrix) const
 	{
 		if (clipXY(pos.x, pos.y))
 		{
-			STRUCTURE *psStruct = buildBlueprint();
-			ASSERT_OR_RETURN(, psStruct != nullptr, "buildBlueprint returned nullptr");
-			renderStructure(psStruct, viewMatrix, perspectiveViewMatrix);
-
-			objmemDestroy(psStruct, false);
+			auto optStruct = buildBlueprint();
+			ASSERT_OR_RETURN(, optStruct.has_value(), "buildBlueprint returned nullopt");
+			renderStructure(&*optStruct, viewMatrix, perspectiveViewMatrix);
 		}
 	}
 
@@ -688,18 +686,28 @@ static Blueprint getTileBlueprint(int mapX, int mapY)
 
 STRUCTURE *getTileBlueprintStructure(int mapX, int mapY)
 {
-	static STRUCTURE *psStruct = nullptr;
+	static optional<STRUCTURE> optStruct;
 
 	Blueprint blueprint = getTileBlueprint(mapX, mapY);
 	if (blueprint.state == SS_BLUEPRINT_PLANNED)
 	{
-		if (psStruct)
+		if (optStruct)
 		{
 			// Delete previously returned structure, if any.
-			objmemDestroy(psStruct, false);
+			optStruct.reset();
+		}
+		auto b = blueprint.buildBlueprint();
+		// Don't use `operator=(optional&&)` to avoid declaring custom copy/move-assignment operators
+		// for `STRUCTURE` (more specifically, for `SIMPLE_OBJECT`, which has some const-qualified data members).
+		if (b)
+		{
+			optStruct.emplace(*b);
+		}
+		else
+		{
+			optStruct.reset();
 		}
-		psStruct = blueprint.buildBlueprint();
-		return psStruct;  // This blueprint was clicked on.
+		return optStruct.has_value() ? &optStruct.value() : nullptr;  // This blueprint was clicked on.
 	}
 
 	return nullptr;

src/structure.cpp

@@ -1829,11 +1829,11 @@ STRUCTURE *buildStructureDir(STRUCTURE_STATS *pStructureType, UDWORD x, UDWORD y
 	return psBuilding;
 }
 
-STRUCTURE *buildBlueprint(STRUCTURE_STATS const *psStats, Vector3i pos, uint16_t direction, unsigned moduleIndex, STRUCT_STATES state, uint8_t ownerPlayer)
+optional<STRUCTURE> buildBlueprint(STRUCTURE_STATS const *psStats, Vector3i pos, uint16_t direction, unsigned moduleIndex, STRUCT_STATES state, uint8_t ownerPlayer)
 {
-	ASSERT_OR_RETURN(nullptr, psStats != nullptr, "No blueprint stats");
-	ASSERT_OR_RETURN(nullptr, psStats->pIMD[0] != nullptr, "No blueprint model for %s", getStatsName(psStats));
-	ASSERT_OR_RETURN(nullptr, ownerPlayer < MAX_PLAYERS, "invalid ownerPlayer: %" PRIu8 "", ownerPlayer);
+	ASSERT_OR_RETURN(nullopt, psStats != nullptr, "No blueprint stats");
+	ASSERT_OR_RETURN(nullopt, psStats->pIMD[0] != nullptr, "No blueprint model for %s", getStatsName(psStats));
+	ASSERT_OR_RETURN(nullopt, ownerPlayer < MAX_PLAYERS, "invalid ownerPlayer: %" PRIu8 "", ownerPlayer);
 
 	Rotation rot(direction, 0, 0);
 
@@ -1909,9 +1909,7 @@ STRUCTURE *buildBlueprint(STRUCTURE_STATS const *psStats, Vector3i pos, uint16_t
 		}
 	}
 
-	auto& stableBlueprint = GlobalStructContainer().emplace(std::move(blueprint));
-
-	return &stableBlueprint;
+	return blueprint;
 }
 
 static Vector2i defaultAssemblyPointPos(STRUCTURE *psBuilding)

src/structure.h

@@ -32,6 +32,8 @@
 #include "visibility.h"
 #include "baseobject.h"
 
+#include <nonstd/optional.hpp>
+
 // how long to wait between CALL_STRUCT_ATTACKED's - plus how long to flash on radar for
 #define ATTACK_CB_PAUSE		5000
 
@@ -105,7 +107,9 @@ STRUCTURE *buildStructure(STRUCTURE_STATS *pStructureType, UDWORD x, UDWORD y, U
 STRUCTURE *buildStructureDir(STRUCTURE_STATS *pStructureType, UDWORD x, UDWORD y, uint16_t direction, UDWORD player, bool FromSave, uint32_t id);
 STRUCTURE *buildStructureDir(STRUCTURE_STATS *pStructureType, UDWORD x, UDWORD y, uint16_t direction, UDWORD player, bool FromSave);
 /// Create a blueprint structure, with just enough information to render it
-STRUCTURE *buildBlueprint(STRUCTURE_STATS const *psStats, Vector3i xy, uint16_t direction, unsigned moduleIndex, STRUCT_STATES state, uint8_t ownerPlayer);
+/// IMPORTANT: Do not save the reference to this instance anywhere, since it's
+/// not heap-allocated and thus doesn't have a stable address!
+nonstd::optional<STRUCTURE> buildBlueprint(STRUCTURE_STATS const *psStats, Vector3i xy, uint16_t direction, unsigned moduleIndex, STRUCT_STATES state, uint8_t ownerPlayer);
 /* The main update routine for all Structures */
 void structureUpdate(STRUCTURE *psBuilding, bool bMission);