From c75451b34c6374e29f3d6c1dd03220c7cc481386 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tam=C3=A1s=20B=C3=A1lint=20Misius?= <lbphacker@gmail.com>
Date: Fri, 15 Dec 2023 21:51:01 +0100
Subject: [PATCH] Fix pasting sometimes getting interrupted by the particle
 limit

More precisely, fix reaching the particle limit while pasting onto a sim with no stacking, which shouldn't be possible at all, because pasting removes stacking at any position that has particles, and if the sim doesn't already have stacking, in the worst case we should end up filling the screen, which would use exactly as many particles as the limit allows.

The problem was that the removal of stacking happened after all particles were done being pasted, which meant that the particle limit could be reached halfway into the process. The solution is to remove on demand the particles wherever we're pasting one.

This works because assuming there is no stacking in the sim (this is the only case we care about) and that pmap is up to date (it is, we call RecalcFreeParticles early), then a spot that is being pasted over is either free (and therefore there are also slots free in Simulation::parts) or has exactly one particle, which we remove before creating the one we're pasting.
---
 src/simulation/Simulation.cpp | 76 ++++++++++++++++++++++-------------
 1 file changed, 49 insertions(+), 27 deletions(-)

diff --git a/src/simulation/Simulation.cpp b/src/simulation/Simulation.cpp
index 82fce6b7e..be970ee2b 100644
--- a/src/simulation/Simulation.cpp
+++ b/src/simulation/Simulation.cpp
@@ -31,6 +31,52 @@ void Simulation::Load(const GameSave *save, bool includePressure, Vec2<int> bloc
 
 	RecalcFreeParticles(false);
 
+	struct ExistingParticle
+	{
+		int id;
+		Vec2<int> pos;
+	};
+	std::vector<ExistingParticle> existingParticles;
+	auto pasteArea = RES.OriginRect() & RectSized(partP, save->blockSize * CELL);
+	for (int i = 0; i <= parts_lastActiveIndex; i++)
+	{
+		if (parts[i].type)
+		{
+			auto p = Vec2<int>{ int(parts[i].x + 0.5f), int(parts[i].y + 0.5f) };
+			if (pasteArea.Contains(p))
+			{
+				existingParticles.push_back({ i, p });
+			}
+		}
+	}
+	std::sort(existingParticles.begin(), existingParticles.end(), [](const auto &lhs, const auto &rhs) {
+		return std::tie(lhs.pos.Y, lhs.pos.X) < std::tie(rhs.pos.Y, rhs.pos.X);
+	});
+	PlaneAdapter<std::vector<size_t>> existingParticleIndices(pasteArea.Size(), existingParticles.size());
+	{
+		auto lastPos = Vec2<int>{ -1, -1 }; // not a valid pos in existingParticles
+		for (auto it = existingParticles.begin(); it != existingParticles.end(); ++it)
+		{
+			if (lastPos != it->pos)
+			{
+				existingParticleIndices[it->pos - pasteArea.TopLeft] = it - existingParticles.begin();
+				lastPos = it->pos;
+			}
+		}
+	}
+	auto removeExistingParticles = [this, pasteArea, &existingParticles, &existingParticleIndices](Vec2<int> p) {
+		auto rp = p - pasteArea.TopLeft;
+		if (existingParticleIndices.Size().OriginRect().Contains(rp))
+		{
+			auto index = existingParticleIndices[rp];
+			for (auto it = existingParticles.begin() + index; it != existingParticles.end() && it->pos == p; ++it)
+			{
+				kill_part(it->id);
+			}
+			existingParticleIndices[rp] = existingParticles.size();
+		}
+	};
+
 	std::map<unsigned int, unsigned int> soapList;
 	for (int n = 0; n < NPART && n < save->particlesCount; n++)
 	{
@@ -69,9 +115,6 @@ void Simulation::Load(const GameSave *save, bool includePressure, Vec2<int> bloc
 			continue;
 		}
 
-		// Mark location to be cleaned of existing particles.
-		pmap[y][x] = -1;
-
 		if (elements[tempPart.type].CreateAllowed)
 		{
 			if (!(*(elements[tempPart.type].CreateAllowed))(this, -3, int(tempPart.x + 0.5f), int(tempPart.y + 0.5f), tempPart.type))
@@ -80,6 +123,8 @@ void Simulation::Load(const GameSave *save, bool includePressure, Vec2<int> bloc
 			}
 		}
 
+		removeExistingParticles({ x, y });
+
 		// Allocate particle (this location is guaranteed to be empty due to "full scan" logic above)
 		if (pfree == -1)
 			break;
@@ -171,35 +216,12 @@ void Simulation::Load(const GameSave *save, bool includePressure, Vec2<int> bloc
 		{
 			parts[i].tmp3 = 0;
 		}
-
-		if (!parts[i].type)
-		{
-			continue;
-		}
-
-		// Mark to be preserved in the loop below.
-		parts[i].type |= 1 << PMAPBITS;
 	}
 	parts_lastActiveIndex = NPART-1;
 	force_stacking_check = true;
 	Element_PPIP_ppip_changed = 1;
 
-	// Loop through particles to find particles in need of being killed
-	for (int i = 0; i <= parts_lastActiveIndex; i++)
-	{
-		if (parts[i].type)
-		{
-			int x = int(parts[i].x + 0.5f);
-			int y = int(parts[i].y + 0.5f);
-			bool preserve = parts[i].type & (1 << PMAPBITS);
-			parts[i].type &= ~(1 << PMAPBITS);
-			if (pmap[y][x] == -1 && !preserve)
-			{
-				kill_part(i);
-			}
-		}
-	}
-
+	// Sort out pmap, just to be on the safe side.
 	RecalcFreeParticles(false);
 
 	// fix SOAP links using soapList, a map of old particle ID -> new particle ID