patern_preview: Adding patern preview

This adds a preview of the patern placement, checking out of bound

src/main.cpp

@@ -25,6 +25,7 @@
 #include <selection_menu.hpp>
 #include <selection.hpp>
 #include <paterns_menu.hpp>
+#include <patern_preview.hpp>
 
 int main(int ac, char **av) {
   std::shared_ptr<gol::ctx> context = std::make_shared<gol::ctx>();
@@ -107,6 +108,7 @@ int main(int ac, char **av) {
   context->selection_menu = std::make_shared<gol::SelectionMenu>(context);
   context->selection = std::make_shared<gol::Selection>(context);
   context->paterns_menu = std::make_shared<gol::PaternsMenu>(context);
+  context->patern_preview = std::make_shared<gol::PaternPreview>(context);
 
   // Speed handling values
   float sim_speed = 1.0f;
@@ -136,6 +138,7 @@ int main(int ac, char **av) {
 
     // Selection behaviour
     context->selection->update();
+    context->patern_preview->update();
     context->selection_menu->update();
     context->settings_menu->update();
 
@@ -154,6 +157,7 @@ int main(int ac, char **av) {
     ClearBackground(BLACK);
     context->render->display(context->world);
     context->selection->display();
+    context->patern_preview->display();
     // Start ImGui frame
     rlImGuiBegin();
     context->control_menu->display();

src/patern_preview.cpp

@@ -0,0 +1,65 @@
+/*
+* File name: patern_preview.cpp
+* Author: lejulien
+* Date created: 01-01-1970 00:59:59
+// Date modified: 12-01-2026 21:30:10
+* ------
+*/
+
+#include <imgui.h>
+#include <raylib.h>
+#include <rlImGui.h>
+
+#include <patern_preview.hpp>
+#include <paterns_menu.hpp>
+#include <settings_menu.hpp>
+#include <snapping.hpp>
+#include <world.hpp>
+
+namespace gol {
+
+PaternPreview::PaternPreview(std::shared_ptr<ctx> context)
+    : context_(context) {}
+
+void PaternPreview::start() { is_started = true; }
+
+void PaternPreview::update() {
+  if (!is_started) return;
+  mouse_pos_ = GetMousePosition();
+  if (ImGui::IsMouseClicked(1)) {
+    is_started = false;
+    return;
+  }
+  // if right click stop the preview
+  // if left click, apply patern to current world
+  // mouse should pass through any present windows
+}
+
+void PaternPreview::display() {
+  if (!is_started) return;
+  std::cout << "preview display started " << std::endl;
+  auto cell_size = context_->settings_menu->getCellSize();
+  auto mouse_in_grid =
+      screenToGrid(mouse_pos_, context_->settings_menu->getCellSize());
+  bool is_unplacable =
+      ((mouse_in_grid.x + context_->paterns_menu->patern_width_ >
+        context_->world->getWidth()) ||
+       (mouse_in_grid.y + context_->paterns_menu->patern_height_ >
+        context_->world->getHeight()));
+  std::cout << "mx:" << mouse_in_grid.x << ", my:" << mouse_in_grid.y
+            << ", cs:" << context_->settings_menu->getCellSize() << std::endl;
+  for (int j = 0; j < context_->paterns_menu->patern_height_; j++) {
+    for (int i = 0; i < context_->paterns_menu->patern_width_; i++) {
+      auto cell =
+          context_->paterns_menu
+              ->loaded_patern_[i + (j * context_->paterns_menu->patern_width_)];
+      if (cell) {
+        DrawRectangle((i + mouse_in_grid.x) * cell_size,
+                      (j + mouse_in_grid.y) * cell_size, cell_size, cell_size,
+                      (is_unplacable) ? RED : BLUE);
+      }
+    }
+  }
+}
+
+};  // namespace gol

src/paterns_menu.cpp

@@ -14,6 +14,7 @@
 #include <fstream>
 #include <iostream>
 #include <paterns_menu.hpp>
+#include <patern_preview.hpp>
 #include <sstream>
 
 namespace gol {
@@ -63,7 +64,7 @@ bool PaternsMenu::loadPatern(std::string &path) {
     }
   } catch (std::exception &e) {
     std::cerr << "Failure in loading patern : " << path << std::endl;
-    return 1;
+    return false;
   }
   return true;
 }
@@ -77,9 +78,8 @@ void PaternsMenu::display() {
     for (auto patern_name : paterns_name_list_) {
       ImGui::PushID(patern_name.c_str());
       if (ImGui::Button(patern_name.c_str()) &&
-          loadPatern(paterns_paths_list_[patern_name])) {
-        // TODO: If patern is loaded successfuly, start the preview in the
-        // editor
+        loadPatern(paterns_paths_list_[patern_name])) {
+        context_->patern_preview->start();
       }
       ImGui::PopID();
       ImGui::SameLine(ImGui::GetWindowWidth() - 57.);

src/snapping.cpp

@@ -0,0 +1,19 @@
+/*
+* File name: snapping.hpp
+* Author: lejulien
+* Date created: 01-01-1970 00:59:59
+// Date modified: 12-01-2026 21:30:10
+* ------
+*/
+
+#include <snapping.hpp>
+
+Vector2 snapToGrid(Vector2 screen, int cell_size) {
+  return {static_cast<float>(round(screen.x / cell_size) * cell_size),
+          static_cast<float>(round(screen.y / cell_size) * cell_size)};
+}
+
+Vector2i screenToGrid(Vector2 screen, int cell_size) {
+  return {static_cast<int>(round(screen.x / cell_size)),
+          static_cast<int>(round(screen.y / cell_size))};
+}