From 6ea11c9aefae745543801b4c6e6522e75fcfac46 Mon Sep 17 00:00:00 2001
From: Pavel Rojtberg <rojtberg@gmail.com>
Date: Sat, 6 Jun 2020 15:50:31 +0200
Subject: [PATCH] Overlay: ImGuiOverlay - update API to avoid NewFrame/
 EndFrame mismatch

---
 Components/Overlay/include/OgreImGuiOverlay.h |  3 ++-
 Components/Overlay/src/OgreImGuiOverlay.cpp   | 10 ++++++++--
 Samples/Simple/include/ImGuiDemo.h            | 16 +++++++---------
 3 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/Components/Overlay/include/OgreImGuiOverlay.h b/Components/Overlay/include/OgreImGuiOverlay.h
index f78f6f80612..6aa12b69326 100644
--- a/Components/Overlay/include/OgreImGuiOverlay.h
+++ b/Components/Overlay/include/OgreImGuiOverlay.h
@@ -23,7 +23,8 @@ class _OgreOverlayExport ImGuiOverlay : public Overlay
     /// must be called before first show()
     ImFont* addFont(const String& name, const String& group OGRE_RESOURCE_GROUP_INIT);
 
-    static void NewFrame(const FrameEvent& evt);
+    static void NewFrame();
+    OGRE_DEPRECATED static void NewFrame(const FrameEvent& evt) { NewFrame(); }
 
     void _findVisibleObjects(Camera* cam, RenderQueue* queue, Viewport* vp);
 
diff --git a/Components/Overlay/src/OgreImGuiOverlay.cpp b/Components/Overlay/src/OgreImGuiOverlay.cpp
index 68db4406dcb..97577bdb45e 100644
--- a/Components/Overlay/src/OgreImGuiOverlay.cpp
+++ b/Components/Overlay/src/OgreImGuiOverlay.cpp
@@ -19,6 +19,7 @@
 #include <OgreRenderQueue.h>
 #include <OgreFrameListener.h>
 #include <OgreRoot.h>
+#include <OgreTimer.h>
 
 namespace Ogre
 {
@@ -125,13 +126,18 @@ void ImGuiOverlay::ImGUIRenderable::createFontTexture()
 
     mFontTex->getBuffer()->blitFromMemory(PixelBox(Box(0, 0, width, height), PF_BYTE_RGBA, pixels));
 }
-void ImGuiOverlay::NewFrame(const FrameEvent& evt)
+void ImGuiOverlay::NewFrame()
 {
+    static auto lastTime = Root::getSingleton().getTimer()->getMilliseconds();
+    auto now = Root::getSingleton().getTimer()->getMilliseconds();
+
     ImGuiIO& io = ImGui::GetIO();
     io.DeltaTime = std::max<float>(
-        evt.timeSinceLastFrame,
+        float(now - lastTime)/1000,
         1e-4f); // see https://github.com/ocornut/imgui/commit/3c07ec6a6126fb6b98523a9685d1f0f78ca3c40c
 
+    lastTime = now;
+
     // Read keyboard modifiers inputs
     io.KeyAlt = false;
     io.KeySuper = false;
diff --git a/Samples/Simple/include/ImGuiDemo.h b/Samples/Simple/include/ImGuiDemo.h
index d9326642130..258fde65bf2 100644
--- a/Samples/Simple/include/ImGuiDemo.h
+++ b/Samples/Simple/include/ImGuiDemo.h
@@ -7,7 +7,7 @@
 using namespace Ogre;
 using namespace OgreBites;
 
-class _OgreSampleClassExport Sample_ImGui : public SdkSample
+class _OgreSampleClassExport Sample_ImGui : public SdkSample, public RenderTargetListener
 {
     std::unique_ptr<ImGuiInputListener> mImguiListener;
     InputListenerChain mListenerChain;
@@ -21,16 +21,13 @@ class _OgreSampleClassExport Sample_ImGui : public SdkSample
         mInfo["Thumbnail"] = "thumb_imgui.png";
     }
 
-    bool frameStarted(const FrameEvent& e)
+    void preViewportUpdate(const RenderTargetViewportEvent& evt)
     {
-        if(mWindow->isActive())
-        {
-            ImGuiOverlay::NewFrame(e);
+        if(!evt.source->getOverlaysEnabled()) return;
 
-            ImGui::ShowDemoWindow();
-        }
+        ImGuiOverlay::NewFrame();
 
-        return SdkSample::frameStarted(e);
+        ImGui::ShowDemoWindow();
     }
 
     bool keyPressed(const KeyboardEvent& evt) { return mListenerChain.keyPressed(evt); }
@@ -50,11 +47,12 @@ class _OgreSampleClassExport Sample_ImGui : public SdkSample
 
         /*
             NOTE:
-            Custom apps will ASSERT on ImGuiOverlay::NewFrame(e) and not display any UI if they
+            Custom apps will ASSERT on ImGuiOverlay::NewFrame() and not display any UI if they
             have not registered the overlay system by calling mSceneMgr->addRenderQueueListener(mOverlaySystem).
             OgreBites::SampleBrowser does this on behalf of the ImGuiDemo but custom applications will need to
             call this themselves.  See ApplicationContextBase::createDummyScene().
         */
+        mWindow->addListener(this);
 
         mImguiListener.reset(new ImGuiInputListener());
         mListenerChain = InputListenerChain({mTrayMgr.get(), mImguiListener.get(), mCameraMan.get()});