support alternative spritesheet for units below 50% health

src/include/unittype.h

@@ -525,6 +525,7 @@ public:
 	std::string Name;               /// Pretty name shown from the engine
 	int Slot;                       /// Type as number
 	std::string File;               /// Sprite files
+	std::string AltFile;            /// Alternative sprite files
 	std::string ShadowFile;         /// Shadow file
 
 	int Width;                                            /// Sprite width
@@ -665,6 +666,7 @@ public:
 	CUnitStats Stats[PlayerMax];     /// Unit status for each player
 
 	CPlayerColorGraphic *Sprite;     /// Sprite images
+	CPlayerColorGraphic *AltSprite;  /// Alternative sprite images
 	CGraphic *ShadowSprite;          /// Shadow sprite image
 };
 

src/unit/script_unittype.cpp

@@ -512,6 +512,8 @@ static int CclDefineUnitType(lua_State *l)
 
 				if (!strcmp(value, "file")) {
 					type->File = LuaToString(l, -1, k + 1);
+				} else if (!strcmp(value, "alt-file")) {
+					type->AltFile = LuaToString(l, -1, k + 1);
 				} else if (!strcmp(value, "size")) {
 					lua_rawgeti(l, -1, k + 1);
 					CclGetPos(l, &type->Width, &type->Height);
@@ -520,9 +522,15 @@ static int CclDefineUnitType(lua_State *l)
 					LuaError(l, "Unsupported image tag: %s" _C_ value);
 				}
 			}
-			if (redefine && type->Sprite) {
-				CGraphic::Free(type->Sprite);
-				type->Sprite = NULL;
+			if (redefine) {
+				if (type->Sprite && type->Sprite->File != type->File) {
+					CGraphic::Free(type->Sprite);
+					type->Sprite = NULL;
+				}
+				if (type->AltSprite && type->AltSprite->File != type->AltFile) {
+					CGraphic::Free(type->AltSprite);
+					type->AltSprite = NULL;
+				}
 			}
 			if (type->ShadowFile == shadowMarker) {
 				type->ShadowFile = type->File;
@@ -1239,12 +1247,17 @@ static int CclCopyUnitType(lua_State *l)
 	to->Flip = from->Flip;
 	to->Name = toName;
 	to->File = from->File;
+	to->AltFile = from->AltFile;
 	to->Width = from->Width;
 	to->Height = from->Height;
 	if (to->Sprite) {
 		CGraphic::Free(to->Sprite);
 		to->Sprite = NULL;
 	}
+	if (to->AltSprite) {
+		CGraphic::Free(to->AltSprite);
+		to->AltSprite = NULL;
+	}
 	to->ShadowFile = from->ShadowFile;
 	to->ShadowWidth = from->ShadowWidth;
 	to->ShadowHeight = from->ShadowHeight;

src/unit/unit_draw.cpp

@@ -1000,6 +1000,9 @@ void CUnit::Draw(const CViewport &vp) const
 				sprite = resinfo->SpriteWhenEmpty;
 			}
 		}
+	} else if (type->AltSprite && this->Variable[HP_INDEX].Value < (this->Variable[HP_INDEX].Max >> 1)) {
+		// TODO: (timfel) do we need more configurability? This at least is pretty fast to check
+		sprite = type->AltSprite;
 	}
 
 	//

src/unit/unittype.cpp

@@ -536,7 +536,7 @@ CUnitType::CUnitType() :
 	CanAttack(0),
 	Neutral(0),
 	GivesResource(0), PoisonDrain(0), FieldFlags(0), MovementMask(0),
-	Sprite(NULL), ShadowSprite(NULL), ShadowSpriteFrame(0), ShadowScale(1)
+	Sprite(NULL), AltSprite(NULL), ShadowSprite(NULL), ShadowSpriteFrame(0), ShadowScale(1)
 {
 #ifdef USE_MNG
 	memset(&Portrait, 0, sizeof(Portrait));
@@ -588,6 +588,7 @@ CUnitType::~CUnitType()
 	}
 
 	CGraphic::Free(Sprite);
+	CGraphic::Free(AltSprite);
 	CGraphic::Free(ShadowSprite);
 #ifdef USE_MNG
 	if (this->Portrait.Num) {
@@ -1030,6 +1031,14 @@ void LoadUnitTypeSprite(CUnitType &type)
 		}
 	}
 
+	if (!type.AltFile.empty()) {
+		type.AltSprite = CPlayerColorGraphic::New(type.AltFile, type.Width, type.Height);
+		type.AltSprite->Load();
+		if (type.Flip) {
+			type.AltSprite->Flip();
+		}
+	}
+
 #ifdef USE_MNG
 	if (type.Portrait.Num) {
 		for (int i = 0; i < type.Portrait.Num; ++i) {