add basic calendar

src/main.cpp

@@ -149,13 +149,13 @@ int main(int, char**)
         ImGui_ImplWin32_NewFrame();
         ImGui::NewFrame();
 
+        //work calendar app
+        per_frame();
+
         // 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
         if (show_demo_window)
             ImGui::ShowDemoWindow(&show_demo_window);
 
-        //work calendar app
-        per_frame();
-
         // Rendering
         ImGui::Render();
         const float clear_color_with_alpha[4] = { clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w };

src/work-calendar.cpp

@@ -1,6 +1,82 @@
 #include <imgui.h>
 
-void per_frame(){
-    //TODO
-    //ImGui::Begin();
+
+bool is_leap_year(int year) {
+    return  ((year % 4) == 0 && (year % 100) != 0) || year % 400 == 0;
 }
+
+int weekday_from_day(int year, int month, int day) {
+    int a = (14 - month) / 12;
+    int y = year - a;
+    int m = month + (12 * a) - 2;
+    return (day + y + (y / 4) - (y / 100) + (y / 400) + ((31 * m) / 12)) % 7;
+}
+
+int calendar_week_from_day(int year, int month, int day){
+    int days_sum[] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
+    int days = days_sum[month - 1];
+    if(is_leap_year(year) && month > 2)
+        days++;
+    
+    return (10 + days + day - weekday_from_day(year, month, day)) / 7;
+}
+
+int days_per_month(int year, int month){
+    int days_in_month[] = { 31,28,31,30,31,30,31,31,30,31,30,31 };
+    if (month == 2) {
+        return is_leap_year(year) ? 29 : 28;
+    }
+    return days_in_month[month - 1];
+}
+
+void per_frame(){
+    static bool use_work_area = true;
+    static ImGuiWindowFlags flags = ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoSavedSettings;
+    // We demonstrate using the full viewport area or the work area (without menu-bars, task-bars etc.)
+    // Based on your use case you may want one or the other.
+    const ImGuiViewport* viewport = ImGui::GetMainViewport();
+    ImGui::SetNextWindowPos(use_work_area ? viewport->WorkPos : viewport->Pos);
+    ImGui::SetNextWindowSize(use_work_area ? viewport->WorkSize : viewport->Size);
+
+    //Begin
+    ImGui::Begin("Work Calendar", 0, flags);
+
+    for (int month = 1; month <= 12; month++) {
+        ImGui::PushID(month);
+        //month
+        if(ImGui::BeginTable("Month", 8, ImGuiTableFlags_SizingFixedSame | ImGuiTableFlags_NoHostExtendX)) {
+            ImGui::TableSetupColumn("KW");
+            ImGui::TableSetupColumn("Mo");
+            ImGui::TableSetupColumn("Di");
+            ImGui::TableSetupColumn("Mi");
+            ImGui::TableSetupColumn("Do");
+            ImGui::TableSetupColumn("Fr");
+            ImGui::TableSetupColumn("Sa");
+            ImGui::TableSetupColumn("So");
+            ImGui::TableHeadersRow();
+            
+            int offset = weekday_from_day(2025, month, 1);
+            //tage
+            for (int day = 1; day <= days_per_month(2025, month); day++) {
+                int weekday = weekday_from_day(2025, month, day);
+
+                if(weekday == 0 || day == 1){
+                    ImGui::TableNextRow();
+                    ImGui::TableSetColumnIndex(0);
+                    ImGui::Text("%d", calendar_week_from_day(2025, month, day));
+                }
+
+                ImGui::TableSetColumnIndex(weekday + 1);
+                ImGui::Text("%d", day);
+            }
+
+            ImGui::EndTable();
+            if ((month % 4) != 0)
+                ImGui::SameLine();
+        }
+        ImGui::PopID();
+    }
+
+    ImGui::End();
+}
+