13 files changed, 460 insertions, 82 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 043bb2d..96de9a1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,6 +20,7 @@ add_library(ui
   src/widget/button.c
   src/widget/frame.c
   src/widget/label.c
+  src/widget/layout.c
   src/widget/scrollbar.c
   src/widget/table.c
   src/widget/widget.c
diff --git a/include/ui.h b/include/ui.h
index baaa550..b70df59 100644
--- a/include/ui.h
+++ b/include/ui.h
@@ -42,15 +42,19 @@ typedef int uiWidgetId;
 /// Widget type.
 typedef enum uiWidgetType {
   uiTypeButton,
+  uiTypeEdit,
   uiTypeFrame,
   uiTypeLabel,
+  uiTypeLayout,
   uiTypeTable,
   uiTypeMax,
 } uiWidgetType;
 
 typedef struct uiButton uiButton;
+typedef struct uiEdit   uiEdit;
 typedef struct uiFrame  uiFrame;
 typedef struct uiLabel  uiLabel;
+typedef struct uiLayout uiLayout;
 typedef struct uiTable  uiTable;
 typedef struct uiWidget uiWidget;
 
@@ -59,13 +63,33 @@ typedef struct uiPtr {
   uiWidgetType type;
   union {
     uiButton* button;
+    uiEdit*   edit;
     uiFrame*  frame;
     uiLabel*  label;
+    uiLayout* layout;
     uiTable*  table;
     uiWidget* widget;
   };
 } uiPtr;
 
+/// Direction in which a layout widget lays out its children.
+typedef enum uiLayoutDirection {
+  uiVertical,
+  uiHorizontal,
+} uiLayoutDirection;
+
+/// Directions in which a widget stretches.
+///
+/// Stretch determines how the widget occupies the area of its parent widget.
+///
+/// uiStretchNone - the widget has a fixed size.
+/// uiStretchX/Y  - the widget stretches in the X/Y direction.
+typedef enum uiStretch {
+  uiStretchNone = 0,
+  uiStretchX    = 1,
+  uiStretchY    = 2,
+} uiStretch;
+
 /// Mouse button.
 typedef enum uiMouseButton {
   uiLMB,
@@ -145,6 +169,11 @@ typedef struct uiWidgetEvent {
   };
 } uiWidgetEvent;
 
+/// Common construction parameters for widgets.
+typedef struct uiParams {
+  uiStretch stretch;
+} uiParams;
+
 // -----------------------------------------------------------------------------
 // Library.
 
@@ -152,50 +181,55 @@ bool uiInit(void);
 void uiShutdown(void);
 
 // -----------------------------------------------------------------------------
-// Widget pointers.
+// Widget.
 
 uiPtr uiMakeButtonPtr(uiButton*);
+uiPtr uiMakeEditPtr(uiEdit*);
 uiPtr uiMakeFramePtr(uiFrame*);
 uiPtr uiMakeLabelPtr(uiLabel*);
+uiPtr uiMakeLayoutPtr(uiLayout*);
 uiPtr uiMakeTablePtr(uiTable*);
 uiPtr uiMakeWidgetPtr(uiWidget*);
 uiPtr uiNullptr(void);
-bool  uiIsNullptr(uiPtr ptr);
+bool  uiIsNullptr(uiPtr);
 
-uiButton* uiGetButtonPtr(uiPtr ptr);
-uiFrame*  uiGetFramePtr(uiPtr ptr);
-uiLabel*  uiGetLabelPtr(uiPtr ptr);
-uiTable*  uiGetTablePtr(uiPtr ptr);
-
-// -----------------------------------------------------------------------------
-// Widget.
+uiButton* uiGetButtonPtr(uiPtr);
+uiEdit*   uiGetEditPtr(uiPtr);
+uiFrame*  uiGetFramePtr(uiPtr);
+uiLabel*  uiGetLabelPtr(uiPtr);
+uiLayout* uiGetLayoutPtr(uiPtr);
+uiTable*  uiGetTablePtr(uiPtr);
 
 uiWidgetType uiWidgetGetType(const uiWidget*);
-void         uiWidgetSetParent(uiPtr child, uiPtr parent);
-
-// -----------------------------------------------------------------------------
-// Button.
 
-uiButton* uiMakeButton(const char* text);
+void uiPrint(uiPtr);
 
 // -----------------------------------------------------------------------------
 // Frame.
 
 uiFrame* uiMakeFrame(void);
 void     uiDestroyFrame(uiFrame**);
-void     uiResizeFrame(uiFrame*, int width, int height);
 uiSize   uiGetFrameSize(const uiFrame*);
 
 // -----------------------------------------------------------------------------
+// Layout.
+uiLayout* uiMakeLayout(uiPtr parent, uiLayoutDirection);
+
+// -----------------------------------------------------------------------------
+// Button.
+
+uiButton* uiMakeButton(uiPtr parent, const char* text, const uiParams*);
+
+// -----------------------------------------------------------------------------
 // Label.
 
-uiLabel*    uiMakeLabel(const char* text);
+uiLabel*    uiMakeLabel(uiPtr parent, const char* text);
 const char* uiLabelGetText(const uiLabel*);
 
 // -----------------------------------------------------------------------------
 // Table.
 
-uiTable*    uiMakeTable(int rows, int cols, const char** header);
+uiTable*    uiMakeTable(uiPtr parent, int rows, int cols, const char** header);
 void        uiTableClear(uiTable*);
 void        uiTableAddRow(uiTable*, const char** row);
 void        uiTableSet(uiTable*, int row, int col, const char* text);
@@ -203,12 +237,20 @@ const char* uiTableGet(const uiTable*, int row, int col);
 void        uiTableScroll(uiTable*, int row);
 
 // -----------------------------------------------------------------------------
+// Layout.
+
+/// Lay out the widgets in the frame given the frame's new width and height.
+///
+/// This should typically be called whenever the window is resized.
+void uiLayOut(uiFrame*, int width, int height);
+
+// -----------------------------------------------------------------------------
 // Rendering.
 
 void uiRender(const uiFrame*, uiSurface*);
 
 // -----------------------------------------------------------------------------
-// UI Events.
+// UI and user events.
 
 /// Get the widget events.
 /// Return the number of events in the returned array.
@@ -218,9 +260,6 @@ void uiRender(const uiFrame*, uiSurface*);
 /// therefore report zero widget events.
 int uiGetEvents(uiWidgetEvent const**);
 
-// -----------------------------------------------------------------------------
-// User input.
-
 /// Send an input event to the UI.
 /// Return true if the UI requires a redraw.
 bool uiSendEvent(uiFrame*, const uiInputEvent*);
diff --git a/src/constants.h b/src/constants.h
index 47babab..408e3d5 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -1,7 +1,17 @@
+/* Constants used throughout the library.
+ *
+ * All sizes are relative to the font size. Widths are relative to the font
+ * width; heights are relative to the font height. Other sizes are typically
+ * relative to font height.
+ */
 #pragma once
 
-// Maximum number of events that can be stored in a single input loop.
+/// Maximum number of events that can be stored in a single input loop.
 #define MaxWidgetEvents 8
 
-// Width of scroll bars in pixels.
+// TODO: Make this relative to the font width.
+/// Width of scroll bars in pixels.
 #define ScrollbarWidth 32
+
+/// Button border size relative to font height.
+#define ButtonBorderSize 0.1
diff --git a/src/layout.c b/src/layout.c
index 5261eb3..3532928 100644
--- a/src/layout.c
+++ b/src/layout.c
@@ -5,16 +5,59 @@
 
 #include <cassert.h>
 
-#define Min(a, b) ((a) < (b) ? (a) : (b))
+static void LayoutWidget(uiWidget* widget, int width, int height);
 
-static void ResizeTable(uiTable* table, int width, int height) {
+/// Return the area required to fit the text.
+static uiSize GetTextSize(const string* text) {
+  return (uiSize){
+      .width  = (int)(g_ui.font->header.glyph_width * string_length(*text)),
+      .height = (int)g_ui.font->header.glyph_height};
+}
+
+static void ResizeButton(uiButton* button, int width, int height) {
+  assert(button);
+
+  // TODO: Define the button's border. But don't store this. Make it a function
+  //  shared between layout.c and render.c. Define it in a new common.h?
+
+  const uiSize minSize = GetTextSize(&button->text);
+  uiSize       size    = minSize;
+  if (button->widget.stretch & uiStretchX) {
+    size.width = Max(size.width, width);
+  }
+  if (button->widget.stretch & uiStretchY) {
+    size.height = Max(size.height, height);
+  }
+  button->widget.rect.width  = size.width;
+  button->widget.rect.height = size.height;
+}
+
+static void ResizeLabel(uiLabel* label, int width, int height) {
+  assert(label);
+
+  const uiSize minSize = GetTextSize(&label->text);
+  uiSize       size    = minSize;
+  if (label->widget.stretch & uiStretchX) {
+    size.width = Max(size.width, width);
+  }
+  if (label->widget.stretch & uiStretchY) {
+    size.height = Max(size.height, height);
+  }
+  label->widget.rect.width  = size.width;
+  label->widget.rect.height = size.height;
+}
+
+static void LayoutTable(uiTable* table, int width, int height) {
   assert(table);
 
-  if (table->cols == 0) {
+  if ((table->cols == 0) || (table->rows == 0)) {
+    table->widget.rect.width  = 0;
+    table->widget.rect.height = 0;
     return;
   }
 
-  table->height = height;
+  table->widget.rect.width  = width;
+  table->widget.rect.height = height;
 
   // Compute the number of rows that are visible at once.
   table->num_visible_rows =
@@ -121,11 +164,10 @@ static void ResizeTable(uiTable* table, int width, int height) {
     }
 
     // Set scrollbar layout.
-    scrollbar->width  = ScrollbarWidth;
-    scrollbar->height = table->height;
-    scrollbar->handle_height =
-        (int)((double)table->num_visible_rows / (double)table->rows *
-              (double)table->height);
+    scrollbar->width         = ScrollbarWidth;
+    scrollbar->height        = height;
+    scrollbar->handle_height = (int)((double)table->num_visible_rows /
+                                     (double)table->rows * (double)height);
     uiTableScroll(table, table->offset);
   } else { // Scroll bar not visible.
     scrollbar->width         = 0;
@@ -135,31 +177,139 @@ static void ResizeTable(uiTable* table, int width, int height) {
   }
 }
 
-static void ResizeWidget(uiWidget* widget, int width, int height) {
-  assert(widget);
+static void Layout(uiLayout* layout, int width, int height) {
+  assert(layout);
 
-  widget->rect.width  = width;
-  widget->rect.height = height;
+  layout->widget.rect.width  = width;
+  layout->widget.rect.height = height;
+
+  // Resizing a layout can get complicated depending on how much flexibility we
+  // want to support. To start simple:
+  // 1. Let the layout stretch to occupy the given size.
+  // 2. For each child, check whether the child has a fixed width/height or
+  //    if it wants to grow.
+  // 3. Fixed-size widgets get their requested size.
+  // 4. Variably-sized widgets get the remainder of the space uniformly
+  //    distributed among them.
+
+  // First resize fixed-size widgets and compute free area, if any, to determine
+  // the size of stretchable widgets along the layout direction. Then resize
+  // stretchable widgets by uniformly distributing the free area.
+  switch (layout->direction) {
+  case uiVertical: {
+    // Resize fixed-size children and compute free area.
+    int free_area         = height;
+    int stretchable_count = 0; // Number of stretchable widgets.
+    list_foreach(layout->widget.children, child, {
+      if (child->stretch & uiStretchY) {
+        stretchable_count++;
+      } else {
+        LayoutWidget(child, width, free_area);
+        free_area -= child->rect.height;
+      }
+    });
+    if (stretchable_count > 0) {
+      // Resize stretchable children.
+      const int stretchable_widget_size = free_area / stretchable_count;
+      list_foreach(layout->widget.children, child, {
+        if (child->stretch != uiStretchNone) {
+          LayoutWidget(child, width, stretchable_widget_size);
+        } else {
+          LayoutWidget(child, width, height);
+        }
+      });
+    }
+    // Now position all widgets inside the layout.
+    int y = 0;
+    list_foreach(layout->widget.children, child, {
+      child->rect.y = y;
+      y += child->rect.height;
+    });
+    // Layout's width is max of its children.
+    layout->widget.rect.width = 0;
+    list_foreach(layout->widget.children, child, {
+      layout->widget.rect.width =
+          Max(layout->widget.rect.width, child->rect.width);
+    });
+    break;
+  }
+  case uiHorizontal: {
+    // Resize fixed-size children and compute free area.
+    int free_area         = width;
+    int stretchable_count = 0; // Number of stretchable widgets.
+    list_foreach(layout->widget.children, child, {
+      if (child->stretch & uiStretchX) {
+        stretchable_count++;
+      } else {
+        LayoutWidget(child, free_area, height);
+        free_area -= child->rect.width;
+      }
+    });
+    if (stretchable_count > 0) {
+      // Resize stretchable children.
+      const int stretchable_size = free_area / stretchable_count;
+      list_foreach(layout->widget.children, child, {
+        if (child->stretch != uiStretchNone) {
+          LayoutWidget(child, stretchable_size, height);
+        }
+      });
+    }
+    // Now position all widgets inside the layout.
+    int x = 0;
+    list_foreach(layout->widget.children, child, {
+      child->rect.x = x;
+      x += child->rect.width;
+    });
+    // Layout's height is max of its children.
+    layout->widget.rect.height = 0;
+    list_foreach(layout->widget.children, child, {
+      layout->widget.rect.height =
+          Max(layout->widget.rect.height, child->rect.height);
+    });
+    break;
+  }
+  }
+}
+
+static void ResizeFrame(uiFrame* frame, int width, int height) {
+  assert(frame);
+
+  frame->widget.rect.width  = width;
+  frame->widget.rect.height = height;
+
+  list_foreach_mut(
+      frame->widget.children, child, { LayoutWidget(child, width, height); });
+}
+
+void uiLayOut(uiFrame* frame, int width, int height) {
+  assert(frame);
+  LayoutWidget(&frame->widget, width, height);
+}
+
+static void LayoutWidget(uiWidget* widget, int width, int height) {
+  assert(widget);
 
   switch (widget->type) {
+  case uiTypeLayout:
+    Layout((uiLayout*)widget, width, height);
+    break;
   case uiTypeButton:
+    ResizeButton((uiButton*)widget, width, height);
     break;
   case uiTypeFrame:
-    list_foreach_mut(
-        widget->children, child, { ResizeWidget(child, width, height); });
+    ResizeFrame((uiFrame*)widget, width, height);
     break;
   case uiTypeLabel:
+    ResizeLabel((uiLabel*)widget, width, height);
+    break;
+  case uiTypeEdit:
+    // TODO: ResizeEdit()
     break;
   case uiTypeTable:
-    ResizeTable((uiTable*)widget, width, height);
+    LayoutTable((uiTable*)widget, width, height);
     break;
   case uiTypeMax:
     TRAP();
     break;
   }
 }
-
-void uiResizeFrame(uiFrame* frame, int width, int height) {
-  assert(frame);
-  ResizeWidget(&frame->widget, width, height);
-}
diff --git a/src/render.c b/src/render.c
index 51112a9..2fcade6 100644
--- a/src/render.c
+++ b/src/render.c
@@ -19,9 +19,9 @@ static const uiPixel uiPink  = {128, 0, 128, 255};
 /// We store a subsurface separate from the surface so that we can always check
 /// whether a given coordinate is within the bounds of the physical surface.
 typedef struct RenderState {
-  uiSurface surface;    /// Surface of pixels on which the UI is rendered.
-  uiRect    subsurface; /// Subregion where the current UI widget is rendered.
-  uiPoint   pen;        /// Current pen position relative to subsurface.
+  uiSurface surface;    ///< Surface of pixels on which the UI is rendered.
+  uiRect    subsurface; ///< Subregion where the current UI widget is rendered.
+  uiPoint   pen;        ///< Current pen position relative to subsurface.
 } RenderState;
 
 static void RenderWidget(RenderState* state, const uiWidget* widget);
@@ -165,6 +165,13 @@ static void RenderFrame(const uiFrame* frame, RenderState* state) {
   FillRect(&frame->widget.rect, uiBlack, state);
 }
 
+/// Render a button.
+static void RenderButton(const uiButton* button, RenderState* state) {
+  assert(button);
+  assert(state);
+  RenderText(string_data(button->text), string_length(button->text), state);
+}
+
 /// Render a label.
 static void RenderLabel(const uiLabel* label, RenderState* state) {
   assert(label);
@@ -253,14 +260,43 @@ static void RenderTable(const uiTable* table, RenderState* state) {
   }
 }
 
+void uiRender(const uiFrame* frame, uiSurface* surface) {
+  assert(frame);
+  assert(surface);
+
+  RenderWidget(
+      &(RenderState){
+          .surface    = *surface,
+          .subsurface = (uiRect){.x      = 0,
+                                 .y      = 0,
+                                 .width  = surface->width,
+                                 .height = surface->height},
+          .pen        = {.x = 0, .y = 0},
+  },
+      (const uiWidget*)frame);
+}
+
 /// Render a widget.
 static void RenderWidget(RenderState* state, const uiWidget* widget) {
   assert(state);
   assert(widget);
 
+  // A widget's position is relative to its parent's position.
+  // The pen currently points at the parent. Move it to this widget's position
+  // before rendering it, then render the widget's children using this new
+  // position.
+  // The pen's original position must be restored before returning, so save a
+  // copy here.
+  const uiPoint pen = state->pen;
+  state->pen =
+      (uiPoint){state->pen.x + widget->rect.x, state->pen.y + widget->rect.y};
+
   // Render this widget.
   switch (widget->type) {
+  case uiTypeLayout:
+    break;
   case uiTypeButton:
+    RenderButton((const uiButton*)widget, state);
     break;
   case uiTypeFrame:
     RenderFrame((const uiFrame*)widget, state);
@@ -268,6 +304,8 @@ static void RenderWidget(RenderState* state, const uiWidget* widget) {
   case uiTypeLabel:
     RenderLabel((const uiLabel*)widget, state);
     break;
+  case uiTypeEdit:
+    break;
   case uiTypeTable:
     RenderTable((const uiTable*)widget, state);
     break;
@@ -278,20 +316,7 @@ static void RenderWidget(RenderState* state, const uiWidget* widget) {
 
   // Render children.
   list_foreach(widget->children, child, { RenderWidget(state, child); });
-}
 
-void uiRender(const uiFrame* frame, uiSurface* surface) {
-  assert(frame);
-  assert(surface);
-
-  RenderWidget(
-      &(RenderState){
-          .surface    = *surface,
-          .subsurface = (uiRect){.x      = 0,
-                                 .y      = 0,
-                                 .width  = surface->width,
-                                 .height = surface->height},
-          .pen        = {.x = 0, .y = 0},
-  },
-      (const uiWidget*)frame);
+  // Restore the pen.
+  state->pen = pen;
 }
diff --git a/src/ui.c b/src/ui.c
index 4d09584..e281f2f 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -8,6 +8,7 @@
 
 bool uiInit(void) {
   // TODO: Embed the font into the library instead.
+  // TODO: Better error reporting.
   const char* font_path = "../ui/fontbaker/NK57.bin";
   if (!(g_ui.font = LoadFontAtlas(font_path))) {
     return false;
diff --git a/src/widget/button.c b/src/widget/button.c
index f2313fd..d8de266 100644
--- a/src/widget/button.c
+++ b/src/widget/button.c
@@ -2,18 +2,21 @@
 
 #include "widget.h"
 
-uiButton* uiMakeButton(const char* text) {
+uiButton* uiMakeButton(uiPtr parent, const char* text, const uiParams* params) {
   assert(text);
+  assert(params);
 
   uiButton* button = UI_NEW(uiButton);
 
   *button = (uiButton){
       .widget =
           (uiWidget){
-                     .type = uiTypeButton,
-                     .rect = {0},
+                     .type    = uiTypeButton,
+                     .rect    = {0},
+                     .stretch = params->stretch,
                      },
       .text = string_new(text),
   };
+  WidgetSetParent(uiMakeButtonPtr(button), parent);
   return button;
 }
diff --git a/src/widget/frame.c b/src/widget/frame.c
index e1078be..7640e42 100644
--- a/src/widget/frame.c
+++ b/src/widget/frame.c
@@ -3,8 +3,13 @@
 #include "widget.h"
 
 uiFrame* uiMakeFrame(void) {
-  uiFrame* frame     = UI_NEW(uiFrame);
-  frame->widget.type = uiTypeFrame;
+  uiFrame* frame = UI_NEW(uiFrame);
+
+  *frame = (uiFrame){
+      .widget =
+          (uiWidget){.type = uiTypeFrame, .stretch = uiStretchX | uiStretchY}
+  };
+
   return frame;
 }
 
diff --git a/src/widget/label.c b/src/widget/label.c
index 30ca0ec..5c0c00a 100644
--- a/src/widget/label.c
+++ b/src/widget/label.c
@@ -3,22 +3,21 @@
 #include "uiLibrary.h"
 #include "widget.h"
 
-uiLabel* uiMakeLabel(const char* text) {
+uiLabel* uiMakeLabel(uiPtr parent, const char* text) {
   assert(text);
 
   uiLabel* label = UI_NEW(uiLabel);
 
   *label = (uiLabel){
       .widget =
-          (uiWidget){
-                     .type = uiTypeLabel,
+          (uiWidget){.type = uiTypeLabel,
                      .rect =
-                  (uiRect){
-                      .width =
-                          (int)strlen(text) * g_ui.font->header.glyph_width,
-                      .height = g_ui.font->header.glyph_height}},
+                         (uiRect){.width = (int)strlen(text) *
+                                           g_ui.font->header.glyph_width,
+                                  .height = g_ui.font->header.glyph_height}},
       .text = string_new(text),
   };
+  WidgetSetParent(uiMakeLabelPtr(label), parent);
   return label;
 }
 
diff --git a/src/widget/layout.c b/src/widget/layout.c
new file mode 100644
index 0000000..c529c56
--- /dev/null
+++ b/src/widget/layout.c
@@ -0,0 +1,25 @@
+#include "widget.h"
+
+static uiStretch StretchFromDirection(uiLayoutDirection direction) {
+  switch (direction) {
+  case uiHorizontal:
+    return uiStretchX;
+  case uiVertical:
+    return uiStretchY;
+  }
+  assert(false);
+  return uiStretchNone;
+}
+
+uiLayout* uiMakeLayout(uiPtr parent, uiLayoutDirection direction) {
+  uiLayout* layout = UI_NEW(uiLayout);
+
+  *layout = (uiLayout){
+      .widget    = (uiWidget){.type    = uiTypeLayout,
+                              .stretch = StretchFromDirection(direction)},
+      .direction = direction,
+  };
+  WidgetSetParent(uiMakeLayoutPtr(layout), parent);
+
+  return layout;
+}
diff --git a/src/widget/table.c b/src/widget/table.c
index e7d412e..d9a6440 100644
--- a/src/widget/table.c
+++ b/src/widget/table.c
@@ -3,11 +3,12 @@
 #define Min(a, b) ((a) < (b) ? (a) : (b))
 #define Max(a, b) ((a) > (b) ? (a) : (b))
 
-uiTable* uiMakeTable(int rows, int cols, const char** header) {
+uiTable* uiMakeTable(uiPtr parent, int rows, int cols, const char** header) {
   uiTable* table = UI_NEW(uiTable);
 
   *table = (uiTable){
-      .widget = (uiWidget){.type = uiTypeTable},
+      .widget =
+          (uiWidget){.type = uiTypeTable, .stretch = (uiStretchX | uiStretchY)},
       .rows   = rows,
       .cols   = cols,
       .widths = (cols > 0) ? calloc(cols, sizeof(int)) : 0,
@@ -15,6 +16,7 @@ uiTable* uiMakeTable(int rows, int cols, const char** header) {
       .cells  = (rows * cols > 0) ? calloc(rows, sizeof(uiCell*)) : 0,
       .flags  = {0},
   };
+  WidgetSetParent(uiMakeTablePtr(table), parent);
 
   if (header) {
     for (int col = 0; col < cols; ++col) {
@@ -91,13 +93,14 @@ void SyncScrollbarToTable(uiTable* table) {
   assert(table);
   ScrollbarScroll(
       &table->scrollbar, (int)((double)table->offset / (double)table->rows *
-                               (double)table->height));
+                               (double)table->widget.rect.height));
 }
 
 void SyncTableToScrollbar(uiTable* table) {
   assert(table);
-  table->offset = (int)((double)table->scrollbar.handle_y /
-                        (double)table->height * (double)table->rows);
+  table->offset =
+      (int)((double)table->scrollbar.handle_y /
+            (double)table->widget.rect.height * (double)table->rows);
 }
 
 const uiCell* TableGetCell(const uiTable* table, int row, int col) {
diff --git a/src/widget/widget.c b/src/widget/widget.c
index ebcaf10..2c525cc 100644
--- a/src/widget/widget.c
+++ b/src/widget/widget.c
@@ -2,6 +2,8 @@
 
 #include <cassert.h>
 
+#include <stdio.h>
+
 // -----------------------------------------------------------------------------
 // Widget.
 
@@ -30,14 +32,19 @@ void DestroyWidget(uiWidget** ppWidget) {
   UI_DEL(ppWidget);
 }
 
-void uiWidgetSetParent(uiPtr child_, uiPtr parent_) {
+void WidgetSetParent(uiPtr child_, uiPtr parent_) {
   uiWidget* child  = child_.widget;
   uiWidget* parent = parent_.widget;
 
   assert(child);
   assert(parent);
 
-  list_add(parent->children, child);
+  if (!uiIsNullptr(child->parent)) {
+    list_remove(child->parent.widget->children, child);
+  }
+
+  list_push(parent->children, child);
+  child->parent = parent_;
 }
 
 // -----------------------------------------------------------------------------
@@ -58,6 +65,11 @@ uiPtr uiMakeLabelPtr(uiLabel* label) {
   return (uiPtr){.type = uiTypeLabel, .label = label};
 }
 
+uiPtr uiMakeLayoutPtr(uiLayout* layout) {
+  assert(layout);
+  return (uiPtr){.type = uiTypeLayout, .layout = layout};
+}
+
 uiPtr uiMakeTablePtr(uiTable* table) {
   assert(table);
   return (uiPtr){.type = uiTypeTable, .table = table};
@@ -72,6 +84,8 @@ uiPtr uiMakeWidgetPtr(uiWidget* widget) {
     return uiMakeFramePtr((uiFrame*)widget);
   case uiTypeLabel:
     return uiMakeLabelPtr((uiLabel*)widget);
+  case uiTypeLayout:
+    return uiMakeLayoutPtr((uiLayout*)widget);
   case uiTypeTable:
     return uiMakeTablePtr((uiTable*)widget);
   default:
@@ -103,8 +117,99 @@ uiLabel* uiGetLabelPtr(uiPtr ptr) {
   return ptr.label;
 }
 
+uiLayout* uiGetLayoutPtr(uiPtr ptr) {
+  assert(ptr.type == uiTypeLayout);
+  assert(ptr.layout);
+  return ptr.layout;
+}
+
+uiEdit* uiGetEditPtr(uiPtr ptr) {
+  assert(ptr.type == uiTypeEdit);
+  assert(ptr.edit);
+  return ptr.edit;
+}
+
 uiTable* uiGetTablePtr(uiPtr ptr) {
   assert(ptr.type == uiTypeTable);
   assert(ptr.table);
   return ptr.table;
 }
+
+typedef struct PrintState {
+  mstring pad;
+  mstring rect;
+} PrintState;
+
+static void RectToString(uiRect rect, mstring* out) {
+  assert(out);
+  out->length = snprintf(
+      out->str, sizeof(out->str), "rect{(x:%d, y:%d), (w:%d, h:%d)", rect.x,
+      rect.y, rect.width, rect.height);
+}
+
+static void uiPrintRec(uiPtr ptr, PrintState* state) {
+  if (uiIsNullptr(ptr)) {
+    return;
+  }
+  RectToString(ptr.widget->rect, &state->rect);
+  switch (ptr.type) {
+  case uiTypeButton: {
+    const uiButton* button = uiGetButtonPtr(ptr);
+    printf(
+        "%sbutton{rect=%s, text=\"%s\"}\n", mstring_cstr(&state->pad),
+        mstring_cstr(&state->rect), string_cstr(&button->text));
+    break;
+  }
+  case uiTypeLabel: {
+    const uiLabel* label = uiGetLabelPtr(ptr);
+    printf(
+        "%sbutton{rect=%s, text=\"%s\"}\n", mstring_cstr(&state->pad),
+        mstring_cstr(&state->rect), string_cstr(&label->text));
+    break;
+  }
+  case uiTypeLayout: {
+    const uiLayout* layout    = uiGetLayoutPtr(ptr);
+    const char*     direction = "";
+    switch (layout->direction) {
+    case uiHorizontal:
+      direction = "horizontal";
+      break;
+    case uiVertical:
+      direction = "vertical";
+      break;
+    }
+    printf(
+        "%s%s_layout{rect=%s}\n", mstring_cstr(&state->pad), direction,
+        mstring_cstr(&state->rect));
+    break;
+  }
+  case uiTypeFrame: {
+    printf(
+        "%sframe{rect=%s}\n", mstring_cstr(&state->pad),
+        mstring_cstr(&state->rect));
+    break;
+  }
+  case uiTypeTable: {
+    const uiTable* table = uiGetTablePtr(ptr);
+    printf(
+        "%stable{rect=%s}\n", mstring_cstr(&state->pad),
+        mstring_cstr(&state->rect));
+    break;
+  }
+  default:
+    printf("%swidget\n", mstring_cstr(&state->pad));
+    break;
+  }
+  const mstring pad = state->pad;
+  state->pad        = mstring_concat(state->pad, mstring_make("  "));
+  list_foreach(ptr.widget->children, child, {
+    uiPrintRec(uiMakeWidgetPtr(child), state);
+  });
+  state->pad = pad;
+}
+
+void uiPrint(uiPtr ptr) {
+  PrintState state =
+      (PrintState){.pad = mstring_make_empty(), .rect = mstring_make_empty()};
+  uiPrintRec(ptr, &state);
+}
diff --git a/src/widget/widget.h b/src/widget/widget.h
index db11164..7482d38 100644
--- a/src/widget/widget.h
+++ b/src/widget/widget.h
@@ -13,9 +13,16 @@ DEF_LIST(Widget, uiWidget*)
 typedef struct uiWidget {
   uiWidgetType type;
   uiRect       rect;
+  uiStretch    stretch;
+  uiPtr        parent;
   Widget_list  children;
 } uiWidget;
 
+typedef struct uiLayout {
+  uiWidget          widget;
+  uiLayoutDirection direction;
+} uiLayout;
+
 typedef struct uiButton {
   uiWidget widget;
   string   text;
@@ -30,6 +37,11 @@ typedef struct uiLabel {
   string   text;
 } uiLabel;
 
+typedef struct uiEdit {
+  uiWidget widget;
+  string   text;
+} uiEdit;
+
 typedef struct uiScrollbar {
   int width;
   int height;        // Total height: handle plus scrollable area.
@@ -45,7 +57,6 @@ typedef struct uiTable {
   uiWidget    widget;
   int         rows;
   int         cols;
-  int         height; // Height in pixels.
   int*        widths; // Width, in pixels, for each column.
   uiCell*     header; // If non-null, row of 'cols' header cells.
   uiCell**    cells;  // Array of 'rows' rows, each of 'cols' cells.
@@ -57,6 +68,7 @@ typedef struct uiTable {
   } flags;
 } uiTable;
 
+void WidgetSetParent(uiPtr child, uiPtr parent);
 void DestroyWidget(uiWidget** ppWidget);
 
 /// Set the scrollbar handle's y-coordinate, which is clipped to the scrollbar's