Add: [NewGRF] Special value 0x7FFE for VarAction2 results specifying 'return calculated result'.

src/newgrf/newgrf_act2.cpp

@@ -23,6 +23,7 @@
 #include "../safeguards.h"
 
 constexpr uint16_t GROUPID_CALLBACK_FAILED = 0x7FFF; ///< Explicit "failure" result.
+constexpr uint16_t GROUPID_CALCULATED_RESULT = 0x7FFE; ///< Return calculated result from VarAction2.
 
 /**
  * Map the colour modifiers of TTDPatch to those that Open is using.
@@ -420,15 +421,31 @@ static void NewSpriteGroup(ByteReader &buf)
 			std::vector<DeterministicSpriteGroupRange> ranges;
 			ranges.resize(buf.ReadByte());
 			for (auto &range : ranges) {
-				range.group = GetGroupFromGroupID(setid, type, buf.ReadWord());
+				auto groupid = buf.ReadWord();
+				if (groupid == GROUPID_CALCULATED_RESULT) {
+					range.result.calculated_result = true;
+				} else {
+					range.result.group = GetGroupFromGroupID(setid, type, groupid);
+				}
 				range.low   = buf.ReadVarSize(varsize);
 				range.high  = buf.ReadVarSize(varsize);
 			}
 
-			group->default_group = GetGroupFromGroupID(setid, type, buf.ReadWord());
+			auto defgroupid = buf.ReadWord();
-			group->error_group = ranges.empty() ? group->default_group : ranges[0].group;
+			if (defgroupid == GROUPID_CALCULATED_RESULT) {
-			/* nvar == 0 is a special case -- we turn our value into a callback result */
+				group->default_result.calculated_result = true;
-			group->calculated_result = ranges.empty();
+			} else {
+				group->default_result.group = GetGroupFromGroupID(setid, type, defgroupid);
+			}
+			/* 'calculated_result' makes no sense for the 'error' case. Use callback failure (nullptr) instead */
+			group->error_group = ranges.empty() ? group->default_result.group : ranges[0].result.group;
+			/* nvar == 0 is a special case:
+			 * - set "default_result" to "calculated_result".
+			 * - the old value specifies the "error_group". */
+			if (ranges.empty()) {
+				group->default_result.calculated_result = true;
+				group->default_result.group = nullptr;
+			}
 
 			/* Sort ranges ascending. When ranges overlap, this may required clamping or splitting them */
 			std::vector<uint32_t> bounds;
@@ -440,13 +457,13 @@ static void NewSpriteGroup(ByteReader &buf)
 			std::sort(bounds.begin(), bounds.end());
 			bounds.erase(std::unique(bounds.begin(), bounds.end()), bounds.end());
 
-			std::vector<const SpriteGroup *> target;
+			std::vector<DeterministicSpriteGroupResult> target;
 			target.reserve(bounds.size());
 			for (const auto &bound : bounds) {
-				const SpriteGroup *t = group->default_group;
+				auto t = group->default_result;
 				for (const auto &range : ranges) {
 					if (range.low <= bound && bound <= range.high) {
-						t = range.group;
+						t = range.result;
 						break;
 					}
 				}
@@ -455,11 +472,11 @@ static void NewSpriteGroup(ByteReader &buf)
 			assert(target.size() == bounds.size());
 
 			for (uint j = 0; j < bounds.size(); ) {
-				if (target[j] != group->default_group) {
+				if (target[j] != group->default_result) {
 					DeterministicSpriteGroupRange &r = group->ranges.emplace_back();
-					r.group = target[j];
+					r.result = target[j];
 					r.low = bounds[j];
-					while (j < bounds.size() && target[j] == r.group) {
+					while (j < bounds.size() && target[j] == r.result) {
 						j++;
 					}
 					r.high = j < bounds.size() ? bounds[j] - 1 : UINT32_MAX;

src/newgrf_spritegroup.cpp

@@ -224,26 +224,27 @@ static bool RangeHighComparator(const DeterministicSpriteGroupRange &range, uint
 
 	object.last_value = last_value;
 
-	if (this->calculated_result) {
+	auto result = this->default_result;
-		/* nvar == 0 is a special case -- we turn our value into a callback result */
-		return static_cast<CallbackResult>(GB(value, 0, 15));
-	}
 
 	if (this->ranges.size() > 4) {
 		const auto &lower = std::lower_bound(this->ranges.begin(), this->ranges.end(), value, RangeHighComparator);
 		if (lower != this->ranges.end() && lower->low <= value) {
 			assert(lower->low <= value && value <= lower->high);
-			return SpriteGroup::Resolve(lower->group, object, false);
+			result = lower->result;
 		}
 	} else {
 		for (const auto &range : this->ranges) {
 			if (range.low <= value && value <= range.high) {
-				return SpriteGroup::Resolve(range.group, object, false);
+				result = range.result;
+				break;
 			}
 		}
 	}
 
-	return SpriteGroup::Resolve(this->default_group, object, false);
+	if (result.calculated_result) {
+		return static_cast<CallbackResult>(GB(value, 0, 15));
+	}
+	return SpriteGroup::Resolve(result.group, object, false);
 }
 
 

src/newgrf_spritegroup.h

@@ -163,8 +163,15 @@ struct DeterministicSpriteGroupAdjust {
 };
 
 
-struct DeterministicSpriteGroupRange {
+struct DeterministicSpriteGroupResult {
+	bool calculated_result = false;
 	const SpriteGroup *group = nullptr;
+
+	bool operator==(const DeterministicSpriteGroupResult &) const = default;
+};
+
+struct DeterministicSpriteGroupRange {
+	DeterministicSpriteGroupResult result;
 	uint32_t low = 0;
 	uint32_t high = 0;
 };
@@ -175,12 +182,11 @@ struct DeterministicSpriteGroup : SpriteGroup {
 
 	VarSpriteGroupScope var_scope{};
 	DeterministicSpriteGroupSize size{};
-	bool calculated_result = false;
 	std::vector<DeterministicSpriteGroupAdjust> adjusts{};
 	std::vector<DeterministicSpriteGroupRange> ranges{}; // Dynamically allocated
 
 	/* Dynamically allocated, this is the sole owner */
-	const SpriteGroup *default_group = nullptr;
+	DeterministicSpriteGroupResult default_result;
 
 	const SpriteGroup *error_group = nullptr; // was first range, before sorting ranges