From dd1b4f27c89b5baeed26e2518f843ecbbd1e8312 Mon Sep 17 00:00:00 2001
From: Dan Paulat <dpaulat@gmail.com>
Date: Sun, 20 Nov 2022 22:12:05 -0600
Subject: [PATCH] Connect ImGui render to QOpenGLWidgets

---
 scwx-qt/source/scwx/qt/main/main.cpp          |  7 ++-
 .../scwx/qt/manager/resource_manager.cpp      | 56 +++++++++++++++++--
 .../scwx/qt/manager/resource_manager.hpp      |  3 +-
 scwx-qt/source/scwx/qt/map/map_widget.cpp     | 16 ++++++
 4 files changed, 76 insertions(+), 6 deletions(-)

diff --git a/scwx-qt/source/scwx/qt/main/main.cpp b/scwx-qt/source/scwx/qt/main/main.cpp
index 594d9a53..b360aa1e 100644
--- a/scwx-qt/source/scwx/qt/main/main.cpp
+++ b/scwx-qt/source/scwx/qt/main/main.cpp
@@ -21,6 +21,8 @@ int main(int argc, char* argv[])
    scwx::util::Logger::Initialize();
    spdlog::set_level(spdlog::level::debug);
 
+   QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts, true);
+
    QApplication a(argc, argv);
 
    QCoreApplication::setApplicationName("Supercell Wx");
@@ -61,7 +63,7 @@ int main(int argc, char* argv[])
    // Initialize application
    scwx::qt::config::RadarSite::Initialize();
    scwx::qt::manager::SettingsManager::Initialize();
-   scwx::qt::manager::ResourceManager::PreLoad();
+   scwx::qt::manager::ResourceManager::Initialize();
 
    // Run Qt main loop
    int result;
@@ -78,6 +80,9 @@ int main(int argc, char* argv[])
    work.reset();
    threadPool.join();
 
+   // Shutdown application
+   scwx::qt::manager::ResourceManager::Shutdown();
+
    // Shutdown AWS SDK
    Aws::ShutdownAPI(awsSdkOptions);
 
diff --git a/scwx-qt/source/scwx/qt/manager/resource_manager.cpp b/scwx-qt/source/scwx/qt/manager/resource_manager.cpp
index c8cceb1d..ffbd364f 100644
--- a/scwx-qt/source/scwx/qt/manager/resource_manager.cpp
+++ b/scwx-qt/source/scwx/qt/manager/resource_manager.cpp
@@ -2,6 +2,12 @@
 #include <scwx/qt/config/county_database.hpp>
 #include <scwx/qt/util/font.hpp>
 #include <scwx/qt/util/texture_atlas.hpp>
+#include <scwx/util/logger.hpp>
+
+#include <backends/imgui_impl_opengl3.h>
+#include <imgui.h>
+#include <QOffscreenSurface>
+#include <QOpenGLContext>
 
 namespace scwx
 {
@@ -11,20 +17,54 @@ namespace manager
 {
 namespace ResourceManager
 {
-static void LoadFonts();
+static const std::string logPrefix_ = "scwx::qt::manager::ResourceManager";
+static const auto        logger_    = scwx::util::Logger::Create(logPrefix_);
 
-void PreLoad()
+static void InitializeImGui();
+static void LoadFonts();
+static void LoadTextures();
+static void ShutdownImGui();
+
+static std::unique_ptr<QOffscreenSurface> surface_ {};
+
+void Initialize()
 {
+   config::CountyDatabase::Initialize();
+
+   InitializeImGui();
    LoadFonts();
+   LoadTextures();
+}
+
+void Shutdown()
+{
+   ShutdownImGui();
+}
+
+static void InitializeImGui()
+{
+   // Create OpenGL Offscreen Surface
+   surface_ = std::make_unique<QOffscreenSurface>();
+   surface_->create();
+   if (!QOpenGLContext::globalShareContext()->makeCurrent(surface_.get()))
+   {
+      logger_->warn("Failed to initialize offscreen surface");
+   }
+
+   // Initialize ImGui
+   ImGui::CreateContext();
+   ImGui_ImplOpenGL3_Init();
+   QOpenGLContext::globalShareContext()->doneCurrent();
 }
 
 static void LoadFonts()
 {
-   config::CountyDatabase::Initialize();
-
    util::Font::Create(":/res/fonts/din1451alt.ttf");
    util::Font::Create(":/res/fonts/din1451alt_g.ttf");
+}
 
+static void LoadTextures()
+{
    util::TextureAtlas& textureAtlas = util::TextureAtlas::Instance();
    textureAtlas.RegisterTexture("lines/default-1x7",
                                 ":/res/textures/lines/default-1x7.png");
@@ -33,6 +73,14 @@ static void LoadFonts()
    textureAtlas.BuildAtlas(8, 8);
 }
 
+static void ShutdownImGui()
+{
+   QOpenGLContext::globalShareContext()->makeCurrent(surface_.get());
+   ImGui_ImplOpenGL3_Shutdown();
+   ImGui::DestroyContext();
+   QOpenGLContext::globalShareContext()->doneCurrent();
+}
+
 } // namespace ResourceManager
 } // namespace manager
 } // namespace qt
diff --git a/scwx-qt/source/scwx/qt/manager/resource_manager.hpp b/scwx-qt/source/scwx/qt/manager/resource_manager.hpp
index ee30bb8f..797779d2 100644
--- a/scwx-qt/source/scwx/qt/manager/resource_manager.hpp
+++ b/scwx-qt/source/scwx/qt/manager/resource_manager.hpp
@@ -8,7 +8,8 @@ namespace manager
 {
 namespace ResourceManager
 {
-void PreLoad();
+void Initialize();
+void Shutdown();
 } // namespace ResourceManager
 } // namespace manager
 } // namespace qt
diff --git a/scwx-qt/source/scwx/qt/map/map_widget.cpp b/scwx-qt/source/scwx/qt/map/map_widget.cpp
index 1a635255..581d6199 100644
--- a/scwx-qt/source/scwx/qt/map/map_widget.cpp
+++ b/scwx-qt/source/scwx/qt/map/map_widget.cpp
@@ -13,6 +13,8 @@
 #include <scwx/util/threads.hpp>
 #include <scwx/util/time.hpp>
 
+#include <backends/imgui_impl_opengl3.h>
+#include <imgui.h>
 #include <QApplication>
 #include <QColor>
 #include <QDebug>
@@ -682,10 +684,24 @@ void MapWidget::initializeGL()
 void MapWidget::paintGL()
 {
    p->frameDraws_++;
+
+   // Setup ImGui Frame
+   ImGui::GetIO().DisplaySize = {static_cast<float>(size().width()),
+                                 static_cast<float>(size().height())};
+
+   // Start ImGui Frame
+   ImGui_ImplOpenGL3_NewFrame();
+   ImGui::NewFrame();
+
+   // Render QMapLibreGL Map
    p->map_->resize(size());
    p->map_->setFramebufferObject(defaultFramebufferObject(),
                                  size() * pixelRatio());
    p->map_->render();
+
+   // Render ImGui Frame
+   ImGui::Render();
+   ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
 }
 
 void MapWidget::mapChanged(QMapLibreGL::Map::MapChange mapChange)