feat: Add Palette Editor for Enhanced Color Management

- Introduced a new PaletteEditorWidget for visual editing of dungeon palettes, allowing users to select and modify colors.
- Integrated palette editor into DungeonEditorV2, enabling real-time updates and re-rendering of rooms upon palette changes.
- Enhanced GUI layout to include a dedicated palette editor card, improving user experience and accessibility.
- Implemented callback functionality to notify when palette changes occur, ensuring seamless integration with room rendering.

src/app/gui/gui_library.cmake

@@ -8,6 +8,7 @@ set(
   app/gui/canvas.cc
   app/gui/canvas_utils.cc
   app/gui/widgets/palette_widget.cc
+  app/gui/widgets/palette_editor_widget.cc
   app/gui/input.cc
   app/gui/style.cc
   app/gui/color.cc

src/app/gui/widgets/palette_editor_widget.cc

@@ -0,0 +1,176 @@
+#include "palette_editor_widget.h"
+
+#include "absl/strings/str_format.h"
+#include "imgui/imgui.h"
+
+namespace yaze {
+namespace gui {
+
+void PaletteEditorWidget::Initialize(Rom* rom) {
+  rom_ = rom;
+  current_palette_id_ = 0;
+  selected_color_index_ = -1;
+}
+
+void PaletteEditorWidget::Draw() {
+  if (!rom_ || !rom_->is_loaded()) {
+    ImGui::TextColored(ImVec4(1, 0, 0, 1), "ROM not loaded");
+    return;
+  }
+  
+  ImGui::BeginGroup();
+  
+  // Palette selector dropdown
+  DrawPaletteSelector();
+  
+  ImGui::Separator();
+  
+  // Color grid display
+  DrawColorGrid();
+  
+  ImGui::Separator();
+  
+  // Color picker for selected color
+  if (selected_color_index_ >= 0) {
+    DrawColorPicker();
+  } else {
+    ImGui::TextDisabled("Select a color to edit");
+  }
+  
+  ImGui::EndGroup();
+}
+
+void PaletteEditorWidget::DrawPaletteSelector() {
+  auto& dungeon_pal_group = rom_->mutable_palette_group()->dungeon_main;
+  int num_palettes = dungeon_pal_group.size();
+  
+  ImGui::Text("Dungeon Palette:");
+  ImGui::SameLine();
+  
+  if (ImGui::BeginCombo("##PaletteSelect", 
+                        absl::StrFormat("Palette %d", current_palette_id_).c_str())) {
+    for (int i = 0; i < num_palettes; i++) {
+      bool is_selected = (current_palette_id_ == i);
+      if (ImGui::Selectable(absl::StrFormat("Palette %d", i).c_str(), is_selected)) {
+        current_palette_id_ = i;
+        selected_color_index_ = -1;  // Reset color selection
+      }
+      if (is_selected) {
+        ImGui::SetItemDefaultFocus();
+      }
+    }
+    ImGui::EndCombo();
+  }
+}
+
+void PaletteEditorWidget::DrawColorGrid() {
+  auto& dungeon_pal_group = rom_->mutable_palette_group()->dungeon_main;
+  
+  if (current_palette_id_ < 0 || current_palette_id_ >= (int)dungeon_pal_group.size()) {
+    ImGui::TextColored(ImVec4(1, 0, 0, 1), "Invalid palette ID");
+    return;
+  }
+  
+  auto palette = dungeon_pal_group[current_palette_id_];
+  int num_colors = palette.size();
+  
+  ImGui::Text("Colors (%d):", num_colors);
+  
+  // Draw color grid (15 colors per row for good layout)
+  const int colors_per_row = 15;
+  const float color_button_size = 24.0f;
+  
+  for (int i = 0; i < num_colors; i++) {
+    ImGui::PushID(i);
+    
+    // Get color as RGB (0-255)
+    auto color = palette[i];
+    ImVec4 col(color.rgb().x / 255.0f, 
+               color.rgb().y / 255.0f,
+               color.rgb().z / 255.0f,
+               1.0f);
+    
+    // Color button
+    bool is_selected = (i == selected_color_index_);
+    if (is_selected) {
+      ImGui::PushStyleColor(ImGuiCol_Border, ImVec4(1, 1, 0, 1));  // Yellow border
+      ImGui::PushStyleVar(ImGuiStyleVar_FrameBorderSize, 2.0f);
+    }
+    
+    if (ImGui::ColorButton(absl::StrFormat("##color%d", i).c_str(), col,
+                          ImGuiColorEditFlags_NoAlpha | ImGuiColorEditFlags_NoPicker,
+                          ImVec2(color_button_size, color_button_size))) {
+      selected_color_index_ = i;
+      editing_color_ = col;
+    }
+    
+    if (is_selected) {
+      ImGui::PopStyleVar();
+      ImGui::PopStyleColor();
+    }
+    
+    // Tooltip showing color index and SNES value
+    if (ImGui::IsItemHovered()) {
+      ImGui::SetTooltip("Color %d\nSNES: 0x%04X\nRGB: (%d, %d, %d)", 
+                       i, color.snes(),
+                       (int)color.rgb().x, (int)color.rgb().y, (int)color.rgb().z);
+    }
+    
+    // Layout: 15 per row
+    if ((i + 1) % colors_per_row != 0 && i < num_colors - 1) {
+      ImGui::SameLine();
+    }
+    
+    ImGui::PopID();
+  }
+}
+
+void PaletteEditorWidget::DrawColorPicker() {
+  ImGui::SeparatorText(absl::StrFormat("Edit Color %d", selected_color_index_).c_str());
+  
+  auto& dungeon_pal_group = rom_->mutable_palette_group()->dungeon_main;
+  auto palette = dungeon_pal_group[current_palette_id_];  // Get copy, not reference
+  auto original_color = palette[selected_color_index_];
+  
+  // Color picker
+  if (ImGui::ColorEdit3("Color", &editing_color_.x, 
+                       ImGuiColorEditFlags_NoAlpha | ImGuiColorEditFlags_PickerHueWheel)) {
+    // Convert ImGui color (0-1) to SNES color (0-31 per channel)
+    int r = static_cast<int>(editing_color_.x * 31.0f);
+    int g = static_cast<int>(editing_color_.y * 31.0f);
+    int b = static_cast<int>(editing_color_.z * 31.0f);
+    
+    // Create SNES color (15-bit BGR555 format)
+    uint16_t snes_color = (b << 10) | (g << 5) | r;
+    
+    // Update palette in ROM (need to write back through the group)
+    palette[selected_color_index_] = gfx::SnesColor(snes_color);
+    dungeon_pal_group[current_palette_id_] = palette;  // Write back
+    
+    // Notify that palette changed
+    if (on_palette_changed_) {
+      on_palette_changed_(current_palette_id_);
+    }
+  }
+  
+  // Show RGB values
+  ImGui::Text("RGB (0-255): (%d, %d, %d)",
+             (int)(editing_color_.x * 255),
+             (int)(editing_color_.y * 255),
+             (int)(editing_color_.z * 255));
+  
+  // Show SNES BGR555 value
+  ImGui::Text("SNES BGR555: 0x%04X", original_color.snes());
+  
+  // Reset button
+  if (ImGui::Button("Reset to Original")) {
+    editing_color_ = ImVec4(original_color.rgb().x / 255.0f,
+                           original_color.rgb().y / 255.0f,
+                           original_color.rgb().z / 255.0f,
+                           1.0f);
+  }
+}
+
+}  // namespace gui
+}  // namespace yaze
+

src/app/gui/widgets/palette_editor_widget.h

@@ -0,0 +1,56 @@
+#ifndef YAZE_APP_GUI_WIDGETS_PALETTE_EDITOR_WIDGET_H
+#define YAZE_APP_GUI_WIDGETS_PALETTE_EDITOR_WIDGET_H
+
+#include <functional>
+#include <vector>
+
+#include "app/gfx/snes_palette.h"
+#include "app/rom.h"
+#include "imgui/imgui.h"
+
+namespace yaze {
+namespace gui {
+
+/**
+ * @brief Simple visual palette editor with color picker
+ * 
+ * Displays dungeon palettes in a grid, allows editing colors,
+ * and notifies when palettes change so rooms can re-render.
+ */
+class PaletteEditorWidget {
+ public:
+  PaletteEditorWidget() = default;
+  
+  void Initialize(Rom* rom);
+  void Draw();
+  
+  // Callback when palette is modified
+  void SetOnPaletteChanged(std::function<void(int palette_id)> callback) {
+    on_palette_changed_ = callback;
+  }
+  
+  // Get/Set current editing palette
+  int current_palette_id() const { return current_palette_id_; }
+  void set_current_palette_id(int id) { current_palette_id_ = id; }
+  
+ private:
+  void DrawPaletteSelector();
+  void DrawColorGrid();
+  void DrawColorPicker();
+  
+  Rom* rom_ = nullptr;
+  int current_palette_id_ = 0;
+  int selected_color_index_ = -1;
+  
+  // Callback for palette changes
+  std::function<void(int palette_id)> on_palette_changed_;
+  
+  // Temp color for editing (RGB 0-1 range for ImGui)
+  ImVec4 editing_color_{0, 0, 0, 1};
+};
+
+}  // namespace gui
+}  // namespace yaze
+
+#endif  // YAZE_APP_GUI_WIDGETS_PALETTE_EDITOR_WIDGET_H
+