feat: Implement a memory arena system with an ImGui-based visual debugger for allocation visualization.

Made using Gemini

.agent/rules/coding-guidelines.md

@@ -2,6 +2,8 @@
 trigger: always_on
 ---
 
+Code compiles with all warning active and warning as errors.
+use static_cast or reinterpret_cast but not parenthesis for casting.
 No exceptions
 Use [[nodiscard]]
 auto is allowed but when its a pointer add the * and when reference adds the &

Juliet/include/Core/Memory/MemoryArena.h

@@ -10,7 +10,14 @@ namespace Juliet
 {
 
     // --- Paged Memory Architecture ---
-    // [Verifying Rebuild]
+    struct ArenaAllocation
+    {
+        size_t           Offset;
+        size_t           Size;
+        String           Tag;
+        ArenaAllocation* Next;
+    };
+
     struct MemoryBlock
     {
         static constexpr uint32 kMagic = 0xAA55AA55;
@@ -18,6 +25,12 @@ namespace Juliet
         MemoryBlock*            Next;      // Next block in the chain (Arena) or FreeList (Pool)
         size_t                  TotalSize; // Total size of this block (including header)
         size_t                  Used;      // Offset relative to the start of Data
+        
+#if JULIET_DEBUG
+        ArenaAllocation* FirstAllocation = nullptr;
+        uint64           Pad; // Ensure 16-byte alignment (Size 40 -> 48)
+#endif
+
         // Data follows immediately. 
         // We use a helper to access it to avoid C++ flexible array warning issues if strict
         uint8* GetData() { return reinterpret_cast<uint8*>(this + 1); }

Juliet/src/Core/Memory/MemoryArena.cpp

@@ -15,6 +15,21 @@ namespace Juliet
 
     // --- MemoryPool Implementation ---
 
+#if JULIET_DEBUG
+    static void FreeDebugAllocations(MemoryBlock* blk)
+    {
+        if (!blk) return;
+        ArenaAllocation* curr = blk->FirstAllocation;
+        while (curr)
+        {
+            ArenaAllocation* next = curr->Next;
+            SafeFree(curr);
+            curr = next;
+        }
+        blk->FirstAllocation = nullptr;
+    }
+#endif
+
     // Simple First-Fit Allocator
     MemoryBlock* MemoryPool::AllocateBlock(size_t minCapacity)
     {
@@ -57,6 +72,9 @@ namespace Juliet
                 curr->Next  = nullptr;
                 curr->Used  = 0;
                 curr->Magic = MemoryBlock::kMagic;
+#if JULIET_DEBUG
+                curr->FirstAllocation = nullptr;
+#endif
 
 #if JULIET_DEBUG
                 if (curr->TotalSize > sizeof(MemoryBlock))
@@ -87,6 +105,7 @@ namespace Juliet
 
         // Poison Header and Data in Debug
 #if JULIET_DEBUG
+        FreeDebugAllocations(block);
         // 0xDD = Dead Data
         MemSet(block->GetData(), 0xDD, block->TotalSize - sizeof(MemoryBlock));
         block->Magic = 0xDEADBEEF;
@@ -169,6 +188,23 @@ namespace Juliet
         // Commit
         blk->Used += alignmentOffset;
         void* ptr = blk->GetData() + blk->Used;
+        
+#if JULIET_DEBUG
+        ArenaAllocation* node = (ArenaAllocation*)Malloc(sizeof(ArenaAllocation));
+        node->Offset = blk->Used;
+        node->Size = size;
+        node->Tag = tag;
+        node->Next = nullptr;
+        
+        if (!blk->FirstAllocation) blk->FirstAllocation = node;
+        else
+        {
+             ArenaAllocation* t = blk->FirstAllocation;
+             while(t->Next) t = t->Next;
+             t->Next = node;
+        }
+#endif
+        
         blk->Used += size;
 
         return ptr;
@@ -195,6 +231,13 @@ namespace Juliet
                 {
                     // Yes, expand in place
                     blk->Used += (newSize - oldSize);
+#if JULIET_DEBUG
+                    {
+                        ArenaAllocation* t = blk->FirstAllocation;
+                        while (t && t->Next) t = t->Next;
+                        if (t) t->Size += (newSize - oldSize);
+                    }
+#endif
                     return oldPtr;
                 }
             }
@@ -223,6 +266,18 @@ namespace Juliet
         {
             // Yes, we can just rewind the Used pointer
             blk->Used -= size;
+#if JULIET_DEBUG
+            {
+                ArenaAllocation* t = blk->FirstAllocation;
+                ArenaAllocation* prev = nullptr;
+                while (t && t->Next) { prev = t; t = t->Next; }
+                if (t) {
+                    SafeFree(t);
+                    if (prev) prev->Next = nullptr;
+                    else blk->FirstAllocation = nullptr;
+                }
+            }
+#endif
             return true;
         }
 
@@ -249,6 +304,7 @@ namespace Juliet
 
 #if JULIET_DEBUG
         // Poison First Block
+        FreeDebugAllocations(arena->FirstBlock);
         MemSet(arena->FirstBlock->GetData(), 0xCD, arena->FirstBlock->TotalSize - sizeof(MemoryBlock));
 #endif
     }

Juliet/src/Engine/Debug/MemoryDebugger.cpp

@@ -1,17 +1,39 @@
 #include <Core/Common/String.h>
 #include <Core/Memory/EngineArena.h>
-#include <cstdio>
 #include <Engine/Debug/MemoryDebugger.h>
 #include <imgui.h>
 
+#include <algorithm>
+
 namespace Juliet::Debug
 {
     namespace
     {
-        void DrawMemoryArena(String name, const MemoryArena& arena)
+#if JULIET_DEBUG
+        // Generate a stable color from a string tag
+        uint32 GetColorForTag(const String& tag)
+        {
+            uint32      hash = 0;
+            size_t      len  = tag.Size;
+            const char* s    = tag.Data;
+            // Simple FNV-1a style hash
+            for (size_t i = 0; i < len; ++i)
+            {
+                hash = hash * 65599 + (uint8)s[i];
+            }
+            // Use hash to pick a Hue
+            float h = static_cast<float>(hash % 360) / 360.0f;
+            return ImColor::HSV(h, 0.7f, 0.8f);
+        }
+#endif
+
+        void DrawMemoryArena(String name, const MemoryArena& arena, [[maybe_unused]] ArenaAllocation* currentHighlight,
+                             [[maybe_unused]] ArenaAllocation*& outNewHighlight)
         {
             if (ImGui::CollapsingHeader(CStr(name), ImGuiTreeNodeFlags_DefaultOpen))
             {
+                ImGui::PushID(CStr(name));
+
                 // Calculate Stats
                 size_t totalCapacity = 0;
                 size_t totalUsed     = 0;
@@ -26,47 +48,131 @@ namespace Juliet::Debug
                     curr = curr->Next;
                 }
 
-                float progress = 0.0f;
+                ImGui::Text("Used: %zu / %zu bytes (%zu blocks)", totalUsed, totalCapacity, blockCount);
-                if (totalCapacity > 0)
+
+#if JULIET_DEBUG
+                // --- Tree View ---
+                if (ImGui::TreeNode("Allocations List"))
                 {
-                    progress = (float)totalUsed / (float)totalCapacity;
+                    MemoryBlock* blk    = arena.FirstBlock;
+                    int          blkIdx = 0;
+                    while (blk)
+                    {
+                        if (ImGui::TreeNode((void*)blk, "Block %d (%zu bytes)", blkIdx, blk->TotalSize))
+                        {
+                            ArenaAllocation* alloc = blk->FirstAllocation;
+                            while (alloc)
+                            {
+                                bool isHovered = (currentHighlight == alloc);
+                                if (isHovered)
+                                {
+                                    ImGui::PushStyleColor(ImGuiCol_Text, ImVec4(1, 1, 0, 1));
                                 }
 
-                char overlay[64];
+                                ImGuiTreeNodeFlags flags = ImGuiTreeNodeFlags_Leaf | ImGuiTreeNodeFlags_NoTreePushOnOpen;
-                sprintf_s(overlay, "%zu / %zu bytes (%zu blocks)", totalUsed, totalCapacity, blockCount);
+                                if (isHovered)
-                ImGui::ProgressBar(progress, ImVec2(0.0f, 0.0f), overlay);
-
-                ImGui::PushID(CStr(name));
-                if (ImGui::TreeNode("Blocks"))
                                 {
-                    if (ImGui::BeginTable("BlocksTable", 3, ImGuiTableFlags_Borders | ImGuiTableFlags_RowBg | ImGuiTableFlags_Resizable))
+                                    flags |= ImGuiTreeNodeFlags_Selected;
-                    {
-                        ImGui::TableSetupColumn("ID");
-                        ImGui::TableSetupColumn("Used");
-                        ImGui::TableSetupColumn("Capacity");
-                        ImGui::TableHeadersRow();
-
-                        size_t idx = 0;
-                        curr = arena.FirstBlock;
-                        while (curr)
-                        {
-                            ImGui::TableNextRow();
-                            
-                            ImGui::TableSetColumnIndex(0);
-                            ImGui::Text("%zu", idx++);
-                            
-                            ImGui::TableSetColumnIndex(1);
-                            ImGui::Text("%zu", curr->Used);
-                            
-                            ImGui::TableSetColumnIndex(2);
-                            ImGui::Text("%zu", curr->TotalSize);
-                            
-                            curr = curr->Next;
                                 }
-                        ImGui::EndTable();
+
+                                // Use implicit string length from String struct
+                                ImGui::TreeNodeEx(alloc, flags, "[%zu] %.*s (%zu bytes)", alloc->Offset,
+                                                  (int)alloc->Tag.Size, alloc->Tag.Data, alloc->Size);
+
+                                if (ImGui::IsItemHovered())
+                                {
+                                    outNewHighlight = alloc;
+                                }
+                                if (isHovered)
+                                {
+                                    ImGui::PopStyleColor();
+                                }
+
+                                alloc = alloc->Next;
                             }
                             ImGui::TreePop();
                         }
+                        blk = blk->Next;
+                        blkIdx++;
+                    }
+                    ImGui::TreePop();
+                }
+
+                // --- Visual View ---
+                ImGui::Spacing();
+
+                MemoryBlock* blk         = arena.FirstBlock;
+                ImDrawList*  dl          = ImGui::GetWindowDrawList();
+                float        availWidth  = ImGui::GetContentRegionAvail().x;
+                float        blockHeight = 24.0f;
+                ImVec2       startPos    = ImGui::GetCursorScreenPos();
+                ImVec2       pos         = startPos;
+
+                int bIdx = 0;
+                while (blk)
+                {
+                    // Draw Block Frame
+                    ImVec2 rectMin = pos;
+                    auto   rectMax = ImVec2(pos.x + availWidth, pos.y + blockHeight);
+
+                    // Border Color
+                    ImU32 borderColor = (uint32)ImColor::HSV(((float)bIdx * 0.1f), 0.0f, 0.7f);
+                    dl->AddRect(rectMin, rectMax, borderColor);
+
+                    size_t dataSize = blk->TotalSize - sizeof(MemoryBlock);
+                    if (dataSize > 0)
+                    {
+                        double scale = (double)availWidth / (double)dataSize;
+
+                        ArenaAllocation* alloc = blk->FirstAllocation;
+                        while (alloc)
+                        {
+                            float xStart = pos.x + (float)((double)alloc->Offset * scale);
+                            float width  = (float)((double)alloc->Size * scale);
+                            width        = std::max(width, 1.0f);
+
+                            auto aMin = ImVec2(xStart, pos.y + 1);
+                            auto aMax = ImVec2(xStart + width, pos.y + blockHeight - 1);
+
+                            ImU32 color = GetColorForTag(alloc->Tag);
+
+                            if (currentHighlight == alloc)
+                            {
+                                // Highlight
+                                dl->AddRectFilled(aMin, aMax, IM_COL32_WHITE);
+                                dl->AddRect(aMin, aMax, IM_COL32_BLACK);
+                            }
+                            else
+                            {
+                                dl->AddRectFilled(aMin, aMax, color);
+                            }
+
+                            // Hit Test
+                            if (ImGui::IsMouseHoveringRect(aMin, aMax))
+                            {
+                                outNewHighlight = alloc;
+                                ImGui::BeginTooltip();
+                                ImGui::Text("Tag: %.*s", (int)alloc->Tag.Size, alloc->Tag.Data);
+                                ImGui::Text("Size: %zu bytes", alloc->Size);
+                                ImGui::Text("Offset: %zu", alloc->Offset);
+                                ImGui::EndTooltip();
+                            }
+
+                            alloc = alloc->Next;
+                        }
+                    }
+
+                    pos.y += blockHeight + 4;
+                    blk = blk->Next;
+                    bIdx++;
+                }
+
+                // Reserve space for the custom drawing
+                ImGui::Dummy(ImVec2(0, (pos.y - startPos.y)));
+#else
+                ImGui::TextColored(ImVec4(1, 0, 0, 1), "Compile with JULIET_DEBUG for Memory Visualization");
+#endif
+
                 ImGui::PopID();
             }
         }
@@ -74,12 +180,25 @@ namespace Juliet::Debug
 
     void DebugDrawMemoryArena()
     {
+#if JULIET_DEBUG
+        // Cross-frame hover state
+        static ArenaAllocation* s_ConfirmedHovered = nullptr;
+        ArenaAllocation*        frameHovered       = nullptr;
+#else
+        ArenaAllocation* s_ConfirmedHovered = nullptr;
+        ArenaAllocation* frameHovered       = nullptr;
+#endif
+
         if (ImGui::Begin("Memory Debugger"))
         {
-            DrawMemoryArena(ConstString("Game Arena"), *GetGameArena());
+            DrawMemoryArena(ConstString("Game Arena"), *GetGameArena(), s_ConfirmedHovered, frameHovered);
-            DrawMemoryArena(ConstString("Engine Arena"), *GetEngineArena());
+            DrawMemoryArena(ConstString("Engine Arena"), *GetEngineArena(), s_ConfirmedHovered, frameHovered);
-            DrawMemoryArena(ConstString("Scratch Arena"), *GetScratchArena());
+            DrawMemoryArena(ConstString("Scratch Arena"), *GetScratchArena(), s_ConfirmedHovered, frameHovered);
         }
         ImGui::End();
+
+#if JULIET_DEBUG
+        s_ConfirmedHovered = frameHovered;
+#endif
     }
 } // namespace Juliet::Debug

log_direct.txt

@@ -0,0 +1,3 @@
+2> Exe: W:\Classified\Juliet\bin\x64Clang-Debug\JulietApp.exe
+FBuild: OK: clang-Debug
+Time: 0.213s

misc/agent_build.bat

@@ -1,3 +1,3 @@
 @echo off
-rem call misc\shell.bat
+call misc\shell.bat
 fbuild %* -cache