Top down tree rebuild (#41)

Efficient top down rebuild of dynamic tree using SAH and bin sort.
erincatto · Jul 14, 2023 · 7664b7d · 7664b7d
1 parent e28d936
commit 7664b7d
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Showing 5 changed files with 394 additions and 67 deletions.
diff --git a/include/box2d/dynamic_tree.h b/include/box2d/dynamic_tree.h
@@ -31,7 +31,7 @@ typedef struct b2DynamicTree
 	int32_t nodeCount;
 	int32_t nodeCapacity;
 	int32_t freeList;
-	int32_t insertionCount;
+	int32_t proxyCount;
 } b2DynamicTree;
 
 /// Constructing the tree initializes the node pool.
@@ -99,6 +99,19 @@ float b2DynamicTree_GetAreaRatio(const b2DynamicTree* tree);
 /// Build an optimal tree. Very expensive. For testing.
 void b2DynamicTree_RebuildBottomUp(b2DynamicTree* tree);
 
+struct b2ProxyMap
+{
+	void* userData;
+};
+
+/// Get the number of proxies created
+int32_t b2DynamicTree_GetProxyCount(const b2DynamicTree* tree);
+
+/// Rebuild a the tree top down using the surface area heuristic. The provide map array must have length equal
+/// to the proxy count. This map allows you to update your proxy indices since this operation invalidates the original indices.
+/// See b2DynamicTree_GetProxyCount.
+void b2DynamicTree_RebuildTopDownSAH(b2DynamicTree* tree, struct b2ProxyMap* mapArray, int32_t mapCount);
+
 /// Shift the world origin. Useful for large worlds.
 /// The shift formula is: position -= newOrigin
 /// @param newOrigin the new origin with respect to the old origin

diff --git a/samples/collection/sample_dynamic_tree.cpp b/samples/collection/sample_dynamic_tree.cpp
@@ -32,13 +32,14 @@ class DynamicTree : public Sample
 		m_moveFraction = 0.0f;
 		m_moveDelta = 0.1f;
 		m_proxies = nullptr;
+		m_mapArray = nullptr;
 		m_proxyCount = 0;
 		m_proxyCapacity = 0;
 		m_wx = 0.5f;
 		m_wy = 0.5f;
 
-		m_rowCount = 10;
-		m_columnCount = 10;
+		m_rowCount = 20;
+		m_columnCount = 20;
 		memset(&m_tree, 0, sizeof(m_tree));
 		BuildTree();
 		m_timeStamp = 0;
@@ -47,23 +48,26 @@ class DynamicTree : public Sample
 		m_endPoint = {0.0f, 0.0f};
 		m_queryDrag = false;
 		m_rayDrag = false;
-
+		m_topDown = false;
 		m_validate = true;
 	}
 
 	~DynamicTree()
 	{
 		free(m_proxies);
+		free(m_mapArray);
 		b2DynamicTree_Destroy(&m_tree);
 	}
 
 	void BuildTree()
 	{
 		b2DynamicTree_Destroy(&m_tree);
 		free(m_proxies);
+		free(m_mapArray);
 
 		m_proxyCapacity = m_rowCount * m_columnCount;
 		m_proxies = static_cast<Proxy*>(malloc(m_proxyCapacity * sizeof(Proxy)));
+		m_mapArray = static_cast<struct b2ProxyMap*>(malloc(m_proxyCapacity * sizeof(struct b2ProxyMap)));
 		m_proxyCount = 0;
 
 		float y = -4.0f;
@@ -95,12 +99,14 @@ class DynamicTree : public Sample
 
 			y += m_wy;
 		}
+
+		m_topDown = false;
 	}
 
 	void UpdateUI() override
 	{
 		ImGui::SetNextWindowPos(ImVec2(10.0f, 100.0f));
-		ImGui::SetNextWindowSize(ImVec2(230.0f, 220.0f));
+		ImGui::SetNextWindowSize(ImVec2(240.0f, 250.0f));
 		ImGui::Begin("Tree Controls", nullptr, ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize);
 
 		bool changed = false;
@@ -131,6 +137,18 @@ class DynamicTree : public Sample
 		{
 		}
 
+		if (ImGui::Button("Rebuild Top Down"))
+		{
+			assert(m_proxyCount == b2DynamicTree_GetProxyCount(&m_tree));
+			b2DynamicTree_RebuildTopDownSAH(&m_tree, m_mapArray, m_proxyCount);
+			for (int32_t i = 0; i < m_proxyCount; ++i)
+			{
+				Proxy* proxy = static_cast<Proxy*>(m_mapArray[i].userData);
+				proxy->proxyId = i;
+			}
+			m_topDown = true;
+		}
+
 		ImGui::Separator();
 
 		ImGui::Text("mouse button 1: ray cast");
@@ -245,6 +263,17 @@ class DynamicTree : public Sample
 			b2DynamicTree_Validate(&m_tree);
 		}
 
+		if (m_topDown)
+		{
+			g_draw.DrawString(5, m_textLine, "top down");
+			m_textLine += m_textIncrement;
+		}
+		else
+		{
+			g_draw.DrawString(5, m_textLine, "incremental");
+			m_textLine += m_textIncrement;
+		}
+
 		m_timeStamp += 1;
 	}
 
@@ -256,6 +285,7 @@ class DynamicTree : public Sample
 	b2DynamicTree m_tree;
 	int m_rowCount, m_columnCount;
 	Proxy* m_proxies;
+	struct b2ProxyMap* m_mapArray;
 	int m_proxyCapacity;
 	int m_proxyCount;
 	int m_timeStamp;
@@ -270,6 +300,7 @@ class DynamicTree : public Sample
 	bool m_rayDrag;
 	bool m_queryDrag;
 	bool m_validate;
+	bool m_topDown;
 };
 
 static bool QueryCallback(int32_t proxyId, void* userData, void* context)

diff --git a/samples/main.cpp b/samples/main.cpp
@@ -498,13 +498,26 @@ int main(int, char**)
 {
 #if defined(_WIN32)
 	// Enable memory-leak reports
-	_CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE);
-	_CrtSetReportFile(_CRT_WARN, _CRTDBG_FILE_STDOUT);
-	_CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE);
-	_CrtSetReportFile(_CRT_ERROR, _CRTDBG_FILE_STDOUT);
-	_CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE);
-	_CrtSetReportFile(_CRT_ASSERT, _CRTDBG_FILE_STDOUT);
-	_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG);
+	_CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_DEBUG | _CRTDBG_MODE_FILE);
+	_CrtSetReportFile(_CRT_WARN, _CRTDBG_FILE_STDERR);
+	//_CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE);
+	//_CrtSetReportFile(_CRT_ERROR, _CRTDBG_FILE_STDOUT);
+	//_CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE);
+	//_CrtSetReportFile(_CRT_ASSERT, _CRTDBG_FILE_STDOUT);
+	{
+		// Get the current bits
+		//int tmp = _CrtSetDbgFlag(_CRTDBG_REPORT_FLAG);
+
+		// Clear the upper 16 bits and OR in the desired frequency
+		//tmp = (tmp & 0x0000FFFF) | _CRTDBG_CHECK_EVERY_16_DF;
+
+		// Set the new bits
+		//_CrtSetDbgFlag(tmp);
+
+		//_CrtSetDbgFlag(_CRTDBG_CHECK_ALWAYS_DF | _CRTDBG_DELAY_FREE_MEM_DF | _CRTDBG_CHECK_CRT_DF | _CRTDBG_LEAK_CHECK_DF);
+		//_CrtSetDbgFlag(_CRTDBG_CHECK_ALWAYS_DF | _CRTDBG_DELAY_FREE_MEM_DF | _CRTDBG_LEAK_CHECK_DF | _CrtSetDbgFlag(_CRTDBG_REPORT_FLAG));
+		//_CrtSetDbgFlag(_CRTDBG_DELAY_FREE_MEM_DF | _CrtSetDbgFlag(_CRTDBG_REPORT_FLAG));
+	}
 	_CrtSetAllocHook(MyAllocHook);
 	//_CrtSetBreakAlloc(196);
 #endif