Created DungeonEditor and Canvas

src/gui/canvas.cc

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+#include "canvas.h"
+
+#include <imgui/imgui.h>
+
+#include <cmath>
+#include <string>
+
+namespace yaze {
+namespace gui {
+
+void Canvas::Update() {
+  ImVec2 canvas_p0 = ImGui::GetCursorScreenPos();
+  ImVec2 canvas_sz = ImGui::GetContentRegionAvail();
+  auto canvas_p1 = ImVec2(canvas_p0.x + canvas_sz.x, canvas_p0.y + canvas_sz.y);
+
+  // Draw border and background color
+  const ImGuiIO &io = ImGui::GetIO();
+  ImDrawList *draw_list = ImGui::GetWindowDrawList();
+  draw_list->AddRectFilled(canvas_p0, canvas_p1, IM_COL32(32, 32, 32, 255));
+  draw_list->AddRect(canvas_p0, canvas_p1, IM_COL32(255, 255, 255, 255));
+
+  // This will catch our interactions
+  ImGui::InvisibleButton(
+      "canvas", canvas_sz,
+      ImGuiButtonFlags_MouseButtonLeft | ImGuiButtonFlags_MouseButtonRight);
+  const bool is_hovered = ImGui::IsItemHovered();  // Hovered
+  const bool is_active = ImGui::IsItemActive();    // Held
+  const ImVec2 origin(canvas_p0.x + scrolling_.x,
+                      canvas_p0.y + scrolling_.y);  // Lock scrolled origin
+  const ImVec2 mouse_pos_in_canvas(io.MousePos.x - origin.x,
+                                   io.MousePos.y - origin.y);
+
+  // Add first and second point
+  if (is_hovered && !dragging_select_ &&
+      ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
+    points_.push_back(mouse_pos_in_canvas);
+    points_.push_back(mouse_pos_in_canvas);
+    dragging_select_ = true;
+  }
+  if (dragging_select_) {
+    points_.back() = mouse_pos_in_canvas;
+    if (!ImGui::IsMouseDown(ImGuiMouseButton_Left)) dragging_select_ = false;
+  }
+
+  // Pan (we use a zero mouse threshold when there's no context menu)
+  const float mouse_threshold_for_pan = enable_context_menu_ ? -1.0f : 0.0f;
+  if (is_active &&
+      ImGui::IsMouseDragging(ImGuiMouseButton_Right, mouse_threshold_for_pan)) {
+    scrolling_.x += io.MouseDelta.x;
+    scrolling_.y += io.MouseDelta.y;
+  }
+
+  // Context menu (under default mouse threshold)
+  ImVec2 drag_delta = ImGui::GetMouseDragDelta(ImGuiMouseButton_Right);
+  if (enable_context_menu_ && drag_delta.x == 0.0f && drag_delta.y == 0.0f)
+    ImGui::OpenPopupOnItemClick("context", ImGuiPopupFlags_MouseButtonRight);
+  if (ImGui::BeginPopup("context")) {
+    if (dragging_select_) points_.resize(points_.size() - 2);
+    dragging_select_ = false;
+    if (ImGui::MenuItem("Remove one", nullptr, false, points_.Size > 0)) {
+      points_.resize(points_.size() - 2);
+    }
+    ImGui::EndPopup();
+  }
+
+  // Draw grid + all lines in the canvas
+  draw_list->PushClipRect(canvas_p0, canvas_p1, true);
+  if (enable_grid_) {
+    const float GRID_STEP = 64.0f;
+    for (float x = fmodf(scrolling_.x, GRID_STEP); x < canvas_sz.x;
+         x += GRID_STEP)
+      draw_list->AddLine(ImVec2(canvas_p0.x + x, canvas_p0.y),
+                         ImVec2(canvas_p0.x + x, canvas_p1.y),
+                         IM_COL32(200, 200, 200, 40));
+    for (float y = fmodf(scrolling_.y, GRID_STEP); y < canvas_sz.y;
+         y += GRID_STEP)
+      draw_list->AddLine(ImVec2(canvas_p0.x, canvas_p0.y + y),
+                         ImVec2(canvas_p1.x, canvas_p0.y + y),
+                         IM_COL32(200, 200, 200, 40));
+  }
+
+  for (int n = 0; n < points_.Size; n += 2) {
+    draw_list->AddRect(
+        ImVec2(origin.x + points_[n].x, origin.y + points_[n].y),
+        ImVec2(origin.x + points_[n + 1].x, origin.y + points_[n + 1].y),
+        IM_COL32(255, 255, 255, 255), 1.0f);
+  }
+
+  draw_list->PopClipRect();
+}
+
+}  // namespace gui
+}  // namespace yaze

src/gui/canvas.h

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+#ifndef YAZE_GUI_CANVAS_H
+#define YAZE_GUI_CANVAS_H
+
+#include <imgui/imgui.h>
+
+#include <cmath>
+#include <string>
+
+namespace yaze {
+namespace gui {
+class Canvas {
+ public:
+  Canvas() = default;
+
+  void Update();
+
+ private:
+  bool enable_grid_ = true;
+  bool enable_context_menu_ = true;
+  bool dragging_select_ = false;
+
+  std::string title_;
+
+  ImVector<ImVec2> points_;
+  ImVec2 scrolling_;
+};
+}  // namespace gui
+}  // namespace yaze
+
+#endif