diff --git a/src/app/editor/foldhaus_editor.cpp b/src/app/editor/foldhaus_editor.cpp
index 39460fd..6fda7e6 100644
--- a/src/app/editor/foldhaus_editor.cpp
+++ b/src/app/editor/foldhaus_editor.cpp
@@ -200,39 +200,86 @@ TestRender(app_state* State, context* Context, render_command_buffer* RenderBuff
 {
     ui_InterfaceReset(&State->Interface);
     State->Interface.RenderBuffer = RenderBuffer;
+    State->Interface.WindowBounds = Context->WindowBounds;
     
-    ui_PushLayout(&State->Interface, Context->WindowBounds, LayoutDirection_TopDown, MakeString("TestRender Layout"));
+    gs_string A = MakeString("TestRender Layout");
     
-    ui_widget_id Ids[2];
-    
-    gs_string String = MakeString("Select");
-    ui_StartRow(&State->Interface, 2);
-    for (u32 j = 0; j < 2; j++)
+    ui_PushLayout(&State->Interface, A);
     {
-        if (ui_BeginDropdown(&State->Interface, String))
+#if 1
+        ui_column_spec ColumnRules[] = {
+            { UIColumnSize_Fixed, 128 },
+            { UIColumnSize_Fill, 0 },
+            { UIColumnSize_Percent, .5f }
+        };
+        ui_BeginRow(&State->Interface, 3, ColumnRules);
+        
         {
-            for (u32 i = 0; i < State->PanelSystem.PanelDefsCount; i++)
+            ui_Button(&State->Interface, MakeString("B"));
+            ui_Button(&State->Interface, MakeString("B"));
+            ui_Button(&State->Interface, MakeString("B"));
+        }
+        ui_EndRow(&State->Interface);
+        ui_Button(&State->Interface, MakeString("B"));
+        ui_Button(&State->Interface, MakeString("C"));
+#elif 0
+        ui_PushLayout(&State->Interface, MakeString("Outer"));
+        {
+            for (u32 i = 0; i < 3; i++)
             {
-                panel_definition Def = State->PanelSystem.PanelDefs[i];
-                gs_string DefName = MakeString(Def.PanelName, Def.PanelNameLength);
-                if (ui_Button(&State->Interface, DefName))
-                {
-                    
-                }
+                ui_Button(&State->Interface, MakeString("A"));
             }
         }
-        ui_EndDropdown(&State->Interface);
+        ui_PopLayout(&State->Interface);
+        
+        ui_BeginRow(&State->Interface, 2);
+        {
+            ui_PushLayout(&State->Interface, MakeString("TestLayout"));
+            {
+                for (u32 i = 0; i < 5; i++)
+                {
+                    ui_Button(&State->Interface, MakeString("TestButon"));
+                }
+            }
+            ui_PopLayout(&State->Interface);
+            
+            ui_PushLayout(&State->Interface, MakeString("TestLayout"));
+            {
+                ui_Button(&State->Interface, MakeString("TestButon"));
+                TestToggle = ui_Toggle(&State->Interface, MakeString("Toggle"), TestToggle);
+                TestSlider_Value = ui_RangeSlider(&State->Interface, MakeString("TestSlider"), TestSlider_Value, TestSlider_Min, TestSlider_Max);
+                if (ui_BeginDropdown(&State->Interface, MakeString("TestDropdown")))
+                {
+                    ui_Button(&State->Interface, MakeString("TestButon"));
+                    ui_Button(&State->Interface, MakeString("TestButon"));
+                    ui_Button(&State->Interface, MakeString("TestButon"));
+                }
+                ui_EndDropdown(&State->Interface);
+            }
+            ui_PopLayout(&State->Interface);
+        }
+        ui_EndRow(&State->Interface);
+        
+        ui_PushLayout(&State->Interface, MakeString("Outer"));
+        {
+            for (u32 i = 0; i < 3; i++)
+            {
+                ui_Button(&State->Interface, MakeString("B"));
+            }
+        }
+        ui_PopLayout(&State->Interface);
+#else
+        ui_BeginList(&State->Interface, MakeString("Test List"), 10);
+        {
+            for (u32 i = 0; i < 32; i++)
+            {
+                ui_Button(&State->Interface, MakeString("Option"));
+            }
+        }
+        ui_EndList(&State->Interface);
+#endif
     }
-    ui_EndRow(&State->Interface);
-    TestSlider_Value = ui_RangeSlider(&State->Interface, MakeString("Test Slider"), TestSlider_Value, TestSlider_Min, TestSlider_Max);
-    
-    TestToggle = ui_Toggle(&State->Interface, MakeString("test toggle"), TestToggle);
-    
-    ui_Button(&State->Interface, MakeString("Hello"));
-    
     ui_PopLayout(&State->Interface);
-    
-    Assert(!ui_WidgetIdsEqual(Ids[0], Ids[1]));
 }
 
 internal void
@@ -243,9 +290,6 @@ Editor_Render(app_state* State, context* Context, render_command_buffer* RenderB
     
 #if 0
     TestRender(State, Context, RenderBuffer);
-    //ui_widget_id IdTwo = TestRender(State, Context, RenderBuffer);
-    //Assert(ui_WidgetIdsEqual(IdOne, IdTwo));
-    
 #else
     ui_InterfaceReset(&State->Interface);
     State->Interface.RenderBuffer = RenderBuffer;
diff --git a/src/app/editor/panels/foldhaus_panel_animation_timeline.h b/src/app/editor/panels/foldhaus_panel_animation_timeline.h
index e9ec1c8..d66b36a 100644
--- a/src/app/editor/panels/foldhaus_panel_animation_timeline.h
+++ b/src/app/editor/panels/foldhaus_panel_animation_timeline.h
@@ -608,7 +608,7 @@ PlayBar_Render(animation_timeline_state* TimelineState, rect2 Bounds, panel* Pan
     ui_PushLayout(Interface, Bounds, LayoutDirection_TopDown, MakeString("PlayBar Layout"));
     
     ui_FillRect(Interface, Bounds, Interface->Style.PanelBGColors[0]);
-    ui_StartRow(&State->Interface, 4);
+    ui_BeginRow(&State->Interface, 4);
     {
         if (ui_Button(Interface, MakeString("Pause")))
         {
@@ -796,7 +796,7 @@ AnimInfoView_Render(animation_timeline_state* TimelineState, rect2 Bounds, rende
     
     ui_FillRect(&State->Interface, Bounds, Interface->Style.PanelBGColors[0]);
     
-    ui_StartRow(&State->Interface, 2);
+    ui_BeginRow(&State->Interface, 2);
     {
         ui_Label(Interface, MakeString("Active Animation"));
         if (ui_BeginDropdown(Interface, ActiveAnim->Name))
diff --git a/src/app/editor/panels/foldhaus_panel_hierarchy.h b/src/app/editor/panels/foldhaus_panel_hierarchy.h
index 12c9fc2..ec6ca55 100644
--- a/src/app/editor/panels/foldhaus_panel_hierarchy.h
+++ b/src/app/editor/panels/foldhaus_panel_hierarchy.h
@@ -52,7 +52,6 @@ HierarchyView_Render(panel* Panel, rect2 PanelBounds, render_command_buffer* Ren
     // Fill in alternating color rows for the backgrounds
     for (u32 Line = 0; Line < LineCount; Line++)
     {
-        //LineBounds[Line] = ui_ReserveElementBounds(Layout);
         v4 ListItemBGColor = ui_GetListItemBGColor(State->Interface.Style, Line);
         ui_FillRect(&State->Interface, LineBounds[Line], ListItemBGColor);
     }
diff --git a/src/app/editor/panels/foldhaus_panel_profiler.h b/src/app/editor/panels/foldhaus_panel_profiler.h
index 80b7890..f6d1ce8 100644
--- a/src/app/editor/panels/foldhaus_panel_profiler.h
+++ b/src/app/editor/panels/foldhaus_panel_profiler.h
@@ -94,8 +94,13 @@ RenderProfiler_ListVisualization(ui_interface* Interface, ui_widget* Layout, deb
     char Backbuffer[256];
     gs_string String = MakeString(Backbuffer, 0, 256);
     
-    r32 ColumnWidths[] = {256, 128, 128, 128, 128};
-    ui_StartRow(Interface, 5, &ColumnWidths[0]);
+    ui_column_spec ColumnWidths[] = {
+        { UIColumnSize_Fixed, 256 },
+        { UIColumnSize_Fixed, 128 },
+        { UIColumnSize_Fixed, 128 },
+        { UIColumnSize_Fixed, 128 },
+        { UIColumnSize_Fixed, 128 }};
+    ui_BeginRow(Interface, 5, &ColumnWidths[0]);
     {
         ui_Label(Interface, MakeString("Procedure"));
         ui_Label(Interface, MakeString("% Frame"));
@@ -112,7 +117,7 @@ RenderProfiler_ListVisualization(ui_interface* Interface, ui_widget* Layout, deb
         {
             collated_scope_record* CollatedRecord = VisibleFrame->CollatedScopes + n;
             
-            ui_StartRow(Interface, 5, &ColumnWidths[0]);
+            ui_BeginRow(Interface, 5, &ColumnWidths[0]);
             {
                 PrintF(&String, "%S", NameEntry.Name);
                 ui_Label(Interface, String);
@@ -181,7 +186,7 @@ ProfilerView_Render(panel* Panel, rect2 PanelBounds, render_command_buffer* Rend
     
     ui_widget* Layout = ui_PushLayout(&State->Interface, ProcListBounds, LayoutDirection_TopDown, MakeString("Profiler Layout"));
     
-    ui_StartRow(&State->Interface, 4);
+    ui_BeginRow(&State->Interface, 4);
     {
         s64 FrameStartCycles = VisibleFrame->FrameStartCycles;
         s64 FrameTotalCycles = VisibleFrame->FrameEndCycles - VisibleFrame->FrameStartCycles;
@@ -194,7 +199,7 @@ ProfilerView_Render(panel* Panel, rect2 PanelBounds, render_command_buffer* Rend
         
         // NOTE(NAME): Skipping a space for aesthetic reasons, not functional, and could
         // be removed, or used for something else
-        ui_ReserveElementBounds(Layout);
+        ui_ReserveBounds(Layout, true);
         
         if (ui_Button(&State->Interface, MakeString("Resume Recording")))
         {
@@ -203,7 +208,7 @@ ProfilerView_Render(panel* Panel, rect2 PanelBounds, render_command_buffer* Rend
     }
     ui_EndRow(&State->Interface);
     
-    ui_StartRow(&State->Interface, 8);
+    ui_BeginRow(&State->Interface, 8);
     {
         if (ui_Button(&State->Interface, MakeString("Scope View")))
         {
diff --git a/src/app/foldhaus_app.cpp b/src/app/foldhaus_app.cpp
index 90ce10b..c56bcaf 100644
--- a/src/app/foldhaus_app.cpp
+++ b/src/app/foldhaus_app.cpp
@@ -106,7 +106,7 @@ INITIALIZE_APPLICATION(InitializeApplication)
     State->Interface.Style.ListBGHover = v4{ .22f, .22f, .22f, 1.f };
     State->Interface.Style.ListBGSelected = v4{.44f, .44f, .44f, 1.f };
     State->Interface.Style.Margin = v2{5, 5};
-    State->Interface.Style.RowHeight = ui_GetTextLineHeight(State->Interface);
+    State->Interface.Style.RowHeight = ui_GetTextLineHeight(State->Interface) + (2 * State->Interface.Style.Margin.y);
     
     State->Interface.WidgetsCountMax = 4096;
     State->Interface.Widgets = PushArray(&State->Permanent, ui_widget, State->Interface.WidgetsCountMax);
diff --git a/src/app/interface.h b/src/app/interface.h
index c2c0b22..cc20c18 100644
--- a/src/app/interface.h
+++ b/src/app/interface.h
@@ -199,6 +199,13 @@ enum ui_layout_direction
 {
     LayoutDirection_TopDown,
     LayoutDirection_BottomUp,
+    LayoutDirection_Inherit,
+};
+
+struct ui_column
+{
+    r32 XMin;
+    r32 XMax;
 };
 
 struct ui_widget
@@ -225,10 +232,9 @@ struct ui_widget
     
     ui_layout_direction FillDirection;
     
-    b32 DrawHorizontal;
-    u32 ColumnsMax;
-    r32* ColumnWidths;
+    ui_column* Columns;
     u32 ColumnsCount;
+    u32 ColumnsFilled;
     
     // NOTE(pjs): I'm not sure this will stay but
     // its here so that when we end things like a dropdown,
@@ -278,7 +284,10 @@ struct ui_widget_retained_state
 struct ui_interface
 {
     interface_config Style;
+    
     mouse_state Mouse;
+    rect2 WindowBounds;
+    
     render_command_buffer* RenderBuffer;
     
     ui_widget* Widgets;
@@ -325,6 +334,28 @@ ui_WidgetIdsEqual(ui_widget_id A, ui_widget_id B)
     return Result;
 }
 
+internal void
+ui_WidgetSetFlag(ui_widget* Widget, u64 Flag)
+{
+    u64 Value = ((u64)1 << Flag);
+    Widget->Flags = Widget->Flags | Value;
+}
+
+internal void
+ui_WidgetClearFlag(ui_widget* Widget, u64 Flag)
+{
+    u64 Value = ((u64)1 << Flag);
+    Widget->Flags = Widget->Flags & ~Value;
+}
+
+internal bool
+ui_WidgetIsFlagSet(ui_widget Widget, u64 Flag)
+{
+    u64 Value = ((u64)1 << Flag);
+    bool Result = (Widget.Flags & Value);
+    return Result;
+}
+
 internal ui_widget_retained_state*
 ui_GetRetainedState(ui_interface* Interface, ui_widget_id Id)
 {
@@ -374,21 +405,7 @@ ui_CreateWidget(ui_interface* Interface, gs_string String)
     Result->ChildrenRoot = 0;
     Result->ChildrenHead = 0;
     Result->Flags = 0;
-    return Result;
-}
-
-internal void
-ui_WidgetSetFlag(ui_widget* Widget, u64 Flag)
-{
-    u64 Value = ((u64)1 << Flag);
-    Widget->Flags = Widget->Flags | Value;
-}
-
-internal bool
-ui_WidgetIsFlagSet(ui_widget Widget, u64 Flag)
-{
-    u64 Value = ((u64)1 << Flag);
-    bool Result = (Widget.Flags & Value);
+    
     return Result;
 }
 
@@ -406,37 +423,146 @@ ui_MouseClickedRect(ui_interface Interface, rect2 Rect)
 
 // Layout
 
+static rect2
+ui_ReserveBounds(ui_widget* Widget, bool Inset)
+{
+    Assert(Widget->ColumnsCount > 0);
+    rect2 Bounds = {0};
+    u32 ColumnIndex = Widget->ChildCount % Widget->ColumnsCount;
+    
+    ui_column Column = Widget->Columns[ColumnIndex];
+    Bounds.Min.x = Column.XMin;
+    Bounds.Min.y = Widget->RowYAt;
+    Bounds.Max.x = Column.XMax;
+    Bounds.Max.y = Bounds.Min.y + Widget->RowHeight;
+    
+    if (Inset)
+    {
+        Bounds.Min.x += Widget->Margin.x;
+        Bounds.Min.y += Widget->Margin.y;
+        Bounds.Max.x -= Widget->Margin.x;
+        Bounds.Max.y -= Widget->Margin.y;
+    }
+    
+    return Bounds;
+}
+
+internal void
+ui_CommitBounds(ui_widget* Parent, rect2 Bounds)
+{
+    u32 ColumnIndex = Parent->ChildCount % Parent->ColumnsCount;
+    if (ColumnIndex == 0)
+    {
+        switch (Parent->FillDirection)
+        {
+            case LayoutDirection_BottomUp:
+            {
+                Parent->RowYAt = Bounds.Max.y;
+            }break;
+            
+            case LayoutDirection_TopDown:
+            {
+                Parent->RowYAt = Bounds.Min.y - Parent->RowHeight;
+            }break;
+        }
+    }
+}
+
+internal void
+ui_ExpandParentToFit(ui_widget* Widget)
+{
+    ui_widget* Parent = Widget->Parent;
+    switch (Widget->FillDirection)
+    {
+        case LayoutDirection_TopDown:
+        {
+            Parent->Bounds.Min.y = Min(Parent->Bounds.Min.y, Widget->Bounds.Min.y - Parent->Margin.y);
+        }break;
+        
+        case LayoutDirection_BottomUp:
+        {
+            Parent->Bounds.Max.y = Max(Parent->Bounds.Max.y, Widget->Bounds.Max.y + Parent->Margin.y);
+        }break;
+        
+        InvalidDefaultCase;
+    }
+}
+
+internal void
+ui_WidgetCreateColumns(ui_widget* Widget, u32 ColumnsCount, ui_interface* Interface)
+{
+    Widget->Columns = PushArray(Interface->PerFrameMemory, ui_column, ColumnsCount);
+    Widget->ColumnsCount = ColumnsCount;
+    Widget->ColumnsFilled = 0;
+}
+
+internal void
+ui_WidgetInitUniformColumns(ui_widget* Widget)
+{
+    r32 CurrentRowWidth = Rect2Width(Widget->Bounds);
+    r32 ColumnWidth = CurrentRowWidth / Widget->ColumnsCount;
+    for (u32 i = 0; i < Widget->ColumnsCount; i++)
+    {
+        ui_column* Column = Widget->Columns + i;
+        Column->XMin = Widget->Bounds.Min.x + (ColumnWidth * i);
+        Column->XMax = Column->XMin + ColumnWidth;
+    }
+}
+
 internal ui_widget*
-ui_CreateLayoutWidget(ui_interface* Interface, rect2 Bounds, ui_layout_direction FillDir, gs_string Name)
+ui_CreateLayoutWidget(ui_interface* Interface, rect2 Bounds, gs_string Name, ui_layout_direction FillDir = LayoutDirection_Inherit)
 {
     ui_widget* Result = ui_CreateWidget(Interface, Name);
-    //ui_WidgetSetFlag(Result, UIWidgetFlag_DrawOutline);
+    ui_WidgetSetFlag(Result, UIWidgetFlag_DrawOutline);
     
     Result->Bounds = Bounds;
     Result->Margin = Interface->Style.Margin;
     Result->RowHeight = Interface->Style.RowHeight;
-    Result->FillDirection = FillDir;
     
-    switch(FillDir)
+    // Single Column Layout
+    ui_WidgetCreateColumns(Result, 1, Interface);
+    ui_WidgetInitUniformColumns(Result);
+    
+    if (FillDir == LayoutDirection_Inherit && Result->Parent != 0)
+    {
+        Result->FillDirection = Result->Parent->FillDirection;
+    }
+    else
+    {
+        Result->FillDirection = FillDir;
+    }
+    
+    switch(Result->FillDirection)
     {
         case LayoutDirection_BottomUp:
         {
-            Result->RowYAt = Bounds.Min.y + Result->Margin.y;
+            Result->RowYAt = Bounds.Min.y;
         }break;
         
         case LayoutDirection_TopDown:
         {
-            Result->RowYAt = Bounds.Max.y - (Result->RowHeight + Result->Margin.y);
+            Result->RowYAt = Bounds.Max.y - Result->RowHeight;
         }break;
+        
+        InvalidDefaultCase;
     }
     
     return Result;
 }
 
+static ui_widget*
+ui_PushOverlayLayout(ui_interface* Interface, rect2 Bounds, ui_layout_direction FillDir, gs_string Name)
+{
+    ui_widget* Result = ui_CreateLayoutWidget(Interface, Bounds, Name, FillDir);
+    SLLPushOrInit(Interface->DrawOrderRoot, Interface->DrawOrderHead, Result);
+    Interface->ActiveLayout = Result;
+    return Result;
+}
+
 static ui_widget*
 ui_PushLayout(ui_interface* Interface, rect2 Bounds, ui_layout_direction FillDir, gs_string Name)
 {
-    ui_widget* Result = ui_CreateLayoutWidget(Interface, Bounds, FillDir, Name);
+    ui_widget* Result = ui_CreateLayoutWidget(Interface, Bounds, Name, FillDir);
     
     if (Interface->DrawOrderRoot)
     {
@@ -453,124 +579,178 @@ ui_PushLayout(ui_interface* Interface, rect2 Bounds, ui_layout_direction FillDir
 }
 
 static ui_widget*
-ui_PushOverlayLayout(ui_interface* Interface, rect2 Bounds, ui_layout_direction FillDir, gs_string Name)
+ui_PushLayout(ui_interface* Interface, gs_string Name, bool Inset = true)
 {
-    ui_widget* Result = ui_CreateLayoutWidget(Interface, Bounds, FillDir, Name);
-    SLLPushOrInit(Interface->DrawOrderRoot, Interface->DrawOrderHead, Result);
-    Interface->ActiveLayout = Result;
-    return Result;
+    rect2 Bounds = {};
+    ui_layout_direction Direction = LayoutDirection_TopDown;
+    if (Interface->ActiveLayout)
+    {
+        Bounds = ui_ReserveBounds(Interface->ActiveLayout, Inset);
+        Direction = Interface->ActiveLayout->FillDirection;
+    }
+    else
+    {
+        Bounds.Min.x = Interface->WindowBounds.Min.x;
+        Bounds.Min.y = Interface->WindowBounds.Max.y;
+        Bounds.Max.x = Interface->WindowBounds.Max.x;
+        Bounds.Max.y = Interface->WindowBounds.Max.y;
+        
+        if (Inset)
+        {
+            Bounds.Min.x += Interface->Style.Margin.x;
+            Bounds.Max.x -= Interface->Style.Margin.x;
+        }
+        
+        Direction = LayoutDirection_TopDown;
+    }
+    return ui_PushLayout(Interface, Bounds, Direction, Name);
+}
+
+internal void
+ui_ExpandToFitChildren(ui_widget* Parent)
+{
+    v2 Extents = { Parent->Bounds.Max.y, Parent->Bounds.Min.y };
+    for (ui_widget* Child = Parent->ChildrenRoot; Child != 0; Child = Child->Next)
+    {
+        Extents.x = Min(Extents.x, Child->Bounds.Min.y);
+        Extents.y = Max(Extents.y, Child->Bounds.Max.y);
+    }
+    
+    switch(Parent->FillDirection)
+    {
+        case LayoutDirection_BottomUp:
+        {
+            Parent->Bounds.Max.y = Extents.y + Parent->Margin.y;
+        }break;
+        
+        case LayoutDirection_TopDown:
+        {
+            Parent->Bounds.Min.y = Extents.x - Parent->Margin.y;
+        }break;
+        
+        InvalidDefaultCase;
+    }
 }
 
 static void
 ui_PopLayout(ui_interface* Interface)
 {
     Assert(Interface->ActiveLayout != 0);
+    
+    ui_widget* Layout = Interface->ActiveLayout;
+    ui_ExpandToFitChildren(Layout);
+    
     Interface->ActiveLayout = Interface->ActiveLayout->Parent;
+    
+    // NOTE(pjs): This indicates that the parent layout should
+    // expand to fit the layout that we just popped
+    if (Interface->ActiveLayout != 0 &&
+        Interface->ActiveLayout->ChildrenHead == Layout)
+    {
+        ui_CommitBounds(Interface->ActiveLayout, Layout->Bounds);
+    }
 }
 
 static void
-ui_StartRow(ui_interface* Interface, u32 ColumnsMax = 0)
+ui_BeginRow(ui_interface* Interface, u32 ColumnsMax)
 {
-    Interface->ActiveLayout->DrawHorizontal = true;
-    Interface->ActiveLayout->ColumnsMax = ColumnsMax;
-    Interface->ActiveLayout->ColumnWidths = 0;
-    Interface->ActiveLayout->ColumnsCount = 0;
+    ui_widget* Layout = ui_PushLayout(Interface, MakeString("Row"), false);
+    ui_WidgetCreateColumns(Layout, ColumnsMax, Interface);
+    ui_WidgetInitUniformColumns(Layout);
 }
 
-static void
-ui_StartRow(ui_interface* Interface, u32 ColumnsMax, r32* ColumnWidths)
+enum ui_column_size_rule
 {
-    Interface->ActiveLayout->DrawHorizontal = true;
-    Interface->ActiveLayout->ColumnsMax = ColumnsMax;
-    Interface->ActiveLayout->ColumnWidths = ColumnWidths;
-    Interface->ActiveLayout->ColumnsCount = 0;
+    UIColumnSize_Fixed,
+    UIColumnSize_Percent,
+    UIColumnSize_Fill,
+};
+
+struct ui_column_spec
+{
+    ui_column_size_rule Rule;
+    union
+    {
+        r32 Width;
+        r32 Percent;
+    };
+};
+
+static void
+ui_BeginRow(ui_interface* Interface, u32 ColumnsMax, ui_column_spec* ColumnRules)
+{
+    ui_widget* Layout = ui_PushLayout(Interface, MakeString("Row"), false);
+    ui_WidgetCreateColumns(Layout, ColumnsMax, Interface);
+    
+    // First Pass, determine widths of each column, and how much space is left to be divided by the fill columns
+    r32 RowWidth = Rect2Width(Layout->Bounds);
+    r32 RemainingSpace = RowWidth;
+    u32 FillColumnsCount = 0;
+    for (u32 i = 0; i < Layout->ColumnsCount; i++)
+    {
+        ui_column_spec Spec = ColumnRules[i];
+        ui_column* Column = Layout->Columns + i;
+        
+        switch (Spec.Rule)
+        {
+            case UIColumnSize_Fixed:
+            {
+                Column->XMax = Spec.Width;
+                RemainingSpace -= Column->XMax;
+            }break;
+            
+            case UIColumnSize_Percent:
+            {
+                Column->XMax = Spec.Percent * RowWidth;
+                RemainingSpace -= Column->XMax;
+            }break;
+            
+            case UIColumnSize_Fill:
+            {
+                FillColumnsCount += 1;
+            }break;
+            InvalidDefaultCase;
+        }
+    }
+    
+    r32 FillColumnWidth = RemainingSpace / FillColumnsCount;
+    
+    // Second Pass, specify the actual XMin and XMax of each column
+    r32 ColumnStartX = Layout->Bounds.Min.x;
+    for (u32 i = 0; i < Layout->ColumnsCount; i++)
+    {
+        ui_column_spec Spec = ColumnRules[i];
+        ui_column* Column = Layout->Columns + i;
+        
+        r32 ColumnWidth = 0;
+        switch (Spec.Rule)
+        {
+            case UIColumnSize_Fixed:
+            case UIColumnSize_Percent:
+            {
+                ColumnWidth = Column->XMax;
+            }break;
+            
+            case UIColumnSize_Fill:
+            {
+                ColumnWidth = FillColumnWidth;
+            }break;
+        }
+        
+        Column->XMin = ColumnStartX ;
+        Column->XMax = Column->XMin + Max(0, ColumnWidth);
+        ColumnStartX = Column->XMax;
+    }
 }
 
 static void
 ui_EndRow(ui_interface* Interface)
 {
-    Interface->ActiveLayout->DrawHorizontal = false;
-    Interface->ActiveLayout->ColumnWidths = 0;
-    Interface->ActiveLayout->RowYAt -= (Interface->ActiveLayout->RowHeight + Interface->ActiveLayout->Margin.y);
-}
-
-static b32
-ui_TryReserveElementBounds(ui_widget* Widget, rect2* Bounds)
-{
-    b32 Result = true;
-    if (!Widget->DrawHorizontal)
-    {
-        Bounds->Min = { Widget->Bounds.Min.x + Widget->Margin.x, Widget->RowYAt };
-        Bounds->Max = { Widget->Bounds.Max.x - Widget->Margin.x, Bounds->Min.y + Widget->RowHeight };
-        
-        r32 RowOffset = Widget->RowHeight + Widget->Margin.y;
-        switch (Widget->FillDirection)
-        {
-            case LayoutDirection_BottomUp:
-            {
-                Widget->RowYAt += RowOffset;
-            }break;
-            
-            case LayoutDirection_TopDown:
-            {
-                Widget->RowYAt -= RowOffset;
-            }break;
-            
-            InvalidDefaultCase;
-        }
-    }
-    else
-    {
-        if (Widget->ColumnsMax > 0)
-        {
-            Assert(Widget->ColumnsCount < Widget->ColumnsMax);
-            if (Widget->ColumnWidths != 0)
-            {
-                v2 Min = {
-                    Widget->Bounds.Min.x + Widget->Margin.x,
-                    Widget->RowYAt
-                };
-                for (u32 i = 0; i < Widget->ColumnsCount; i++)
-                {
-                    Min.x += Widget->ColumnWidths[i];
-                }
-                Bounds->Min = Min;
-                Bounds->Max = Bounds->Min + v2{
-                    Widget->ColumnWidths[Widget->ColumnsCount] - Widget->Margin.x,
-                    Widget->RowHeight
-                };
-            }
-            else
-            {
-                r32 ElementWidth = Rect2Width(Widget->Bounds) / Widget->ColumnsMax;
-                Bounds->Min = {
-                    Widget->Bounds.Min.x + (ElementWidth * Widget->ColumnsCount) + Widget->Margin.x,
-                    Widget->RowYAt
-                };
-                Bounds->Max = {
-                    Bounds->Min.x + ElementWidth - (Widget->Margin.x * 2),
-                    Bounds->Min.y + Widget->RowHeight
-                };
-            }
-            Widget->ColumnsCount++;
-        }
-        else
-        {
-            Result = false;
-        }
-    }
-    return Result;
-}
-
-static rect2
-ui_ReserveElementBounds(ui_widget* Layout)
-{
-    rect2 Bounds = {0};
-    if (!ui_TryReserveElementBounds(Layout, &Bounds))
-    {
-        InvalidCodePath;
-    }
-    return Bounds;
+    ui_PopLayout(Interface);
+    //ui_widget* Layout = Interface->ActiveLayout;
+    //Layout->DrawHorizontal = false;
+    //Layout->RowYAt -= (Layout->RowHeight + Layout->Margin.y);
+    
 }
 
 static rect2
@@ -578,10 +758,6 @@ ui_LayoutRemaining(ui_widget Layout)
 {
     rect2 Result = Layout.Bounds;
     Result.Max.y = Layout.RowYAt;
-    if (Layout.DrawHorizontal)
-    {
-        Result.Max.y -= Layout.RowHeight;
-    }
     return Result;
 }
 
@@ -625,20 +801,17 @@ ui_EvaluateWidget(ui_interface* Interface, ui_widget* Widget, rect2 Bounds)
         
     }
     
+    Assert(Widget->Parent != 0);
+    ui_CommitBounds(Widget->Parent, Widget->Bounds);
+    
     return Result;
 }
 
 internal ui_eval_result
 ui_EvaluateWidget(ui_interface* Interface, ui_widget* Widget)
 {
-    rect2 Bounds = {0};
     ui_widget* Layout = Interface->ActiveLayout;
-    if (!ui_TryReserveElementBounds(Layout, &Bounds))
-    {
-        // TODO(pjs): This isn't invalid, but Idk when we'd hit this case yet
-        InvalidCodePath;
-    }
-    
+    rect2 Bounds = ui_ReserveBounds(Layout, true);
     return ui_EvaluateWidget(Interface, Widget, Bounds);
 }
 
@@ -781,8 +954,8 @@ ui_EvaluateDropdown(ui_interface* Interface, ui_widget* Widget, ui_eval_result E
             r32 ParentLayoutMaxY = ParentLayout.Bounds.Max.y;
             Direction = LayoutDirection_BottomUp;
             MenuBounds = rect2{
-                v2{ Widget->Bounds.Min.x, Widget->Bounds.Max.y },
-                v2{ Widget->Bounds.Max.x, ParentLayoutMaxY }
+                v2{ Widget->Bounds.Min.x - ParentLayout.Margin.x, Widget->Bounds.Max.y },
+                v2{ Widget->Bounds.Max.x + ParentLayout.Margin.x, ParentLayoutMaxY }
             };
         }
         else
@@ -790,14 +963,15 @@ ui_EvaluateDropdown(ui_interface* Interface, ui_widget* Widget, ui_eval_result E
             r32 ParentLayoutMinY = ParentLayout.Bounds.Min.y;
             Direction = LayoutDirection_TopDown;
             MenuBounds = rect2{
-                v2{ Widget->Bounds.Min.x, ParentLayoutMinY },
-                v2{ Widget->Bounds.Max.x, Widget->Bounds.Min.y }
+                v2{ Widget->Bounds.Min.x - ParentLayout.Margin.x, ParentLayoutMinY },
+                v2{ Widget->Bounds.Max.x + ParentLayout.Margin.x, Widget->Bounds.Min.y }
             };
         }
         
         ui_widget* Layout = ui_PushOverlayLayout(Interface, MenuBounds, Direction, MakeString("WidgetLayout"));
         Layout->Margin.y = 0;
         Layout->WidgetReference = Widget->Id;
+        ui_WidgetClearFlag(Layout, UIWidgetFlag_DrawOutline);
     }
     
     return State->Value;
@@ -913,6 +1087,19 @@ ui_Toggle(ui_interface* Interface, gs_string Text, bool Value)
     return Result;
 }
 
+internal void
+ui_BeginList(ui_interface* Interface, gs_string Text, u32 ViewportRows)
+{
+    ui_widget* Layout = ui_PushLayout(Interface, Text);
+    
+}
+
+internal void
+ui_EndList(ui_interface* Interface)
+{
+    
+}
+
 
 //
 // OLD