Change: Skip creating a RealSpriteGroup when there is only one result.

This avoids checking RSG for empty sets every time they are evaluated.
This might alter behaviour in cases of a malformed NewGRF file.

1 files changed, 42 insertions, 13 deletions

diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index 318c5e8ea..1432c0660 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -109,7 +109,7 @@ public:
 	int skip_sprites;         ///< Number of pseudo sprites to skip before processing the next one. (-1 to skip to end of file)
 
 	/* Currently referenceable spritegroups */
-	SpriteGroup *spritegroups[MAX_SPRITEGROUP + 1];
+	const SpriteGroup *spritegroups[MAX_SPRITEGROUP + 1];
 
 	/** Clear temporary data before processing the next file in the current loading stage */
 	void ClearDataForNextFile()
@@ -4982,7 +4982,7 @@ static void NewSpriteGroup(ByteReader *buf)
 	 *                 otherwise it specifies a number of entries, the exact
 	 *                 meaning depends on the feature
 	 * V feature-specific-data (huge mess, don't even look it up --pasky) */
-	SpriteGroup *act_group = nullptr;
+	const SpriteGroup *act_group = nullptr;
 
 	uint8 feature = buf->ReadByte();
 	if (feature >= GSF_END) {
@@ -5163,24 +5163,53 @@ static void NewSpriteGroup(ByteReader *buf)
 						return;
 					}
 
-					assert(RealSpriteGroup::CanAllocateItem());
-					RealSpriteGroup *group = new RealSpriteGroup();
-					group->nfo_line = _cur.nfo_line;
-					act_group = group;
-
 					grfmsg(6, "NewSpriteGroup: New SpriteGroup 0x%02X, %u loaded, %u loading",
 							setid, num_loaded, num_loading);
 
-					for (uint i = 0; i < num_loaded; i++) {
+					if (num_loaded + num_loading == 1) {
+						/* Avoid creating 'Real' sprite group if only one option. */
 						uint16 spriteid = buf->ReadWord();
-						group->loaded.push_back(CreateGroupFromGroupID(feature, setid, type, spriteid));
-						grfmsg(8, "NewSpriteGroup: + rg->loaded[%i]  = subset %u", i, spriteid);
+						act_group = CreateGroupFromGroupID(feature, setid, type, spriteid);
+						grfmsg(8, "NewSpriteGroup: one result, skipping RealSpriteGroup = subset %u", spriteid);
+						break;
+					}
+
+					std::vector<uint16> loaded;
+					std::vector<uint16> loading;
+
+					for (uint i = 0; i < num_loaded; i++) {
+						loaded.push_back(buf->ReadWord());
+						grfmsg(8, "NewSpriteGroup: + rg->loaded[%i]  = subset %u", i, loaded[i]);
 					}
 
 					for (uint i = 0; i < num_loading; i++) {
-						uint16 spriteid = buf->ReadWord();
-						group->loading.push_back(CreateGroupFromGroupID(feature, setid, type, spriteid));
-						grfmsg(8, "NewSpriteGroup: + rg->loading[%i] = subset %u", i, spriteid);
+						loading.push_back(buf->ReadWord());
+						grfmsg(8, "NewSpriteGroup: + rg->loading[%i] = subset %u", i, loading[i]);
+					}
+
+					if (std::adjacent_find(loaded.begin(),  loaded.end(),  std::not_equal_to<>()) == loaded.end() &&
+						std::adjacent_find(loading.begin(), loading.end(), std::not_equal_to<>()) == loading.end() &&
+						loaded[0] == loading[0])
+					{
+						/* Both lists only contain the same value, so don't create 'Real' sprite group */
+						act_group = CreateGroupFromGroupID(feature, setid, type, loaded[0]);
+						grfmsg(8, "NewSpriteGroup: same result, skipping RealSpriteGroup = subset %u", loaded[0]);
+						break;
+					}
+
+					assert(RealSpriteGroup::CanAllocateItem());
+					RealSpriteGroup *group = new RealSpriteGroup();
+					group->nfo_line = _cur.nfo_line;
+					act_group = group;
+
+					for (uint16 spriteid : loaded) {
+						const SpriteGroup *t = CreateGroupFromGroupID(feature, setid, type, spriteid);
+						group->loaded.push_back(t);
+					}
+
+					for (uint16 spriteid : loading) {
+						const SpriteGroup *t = CreateGroupFromGroupID(feature, setid, type, spriteid);
+						group->loading.push_back(t);
 					}
 
 					break;