From bd680b34b58c8bf6dee8e7e1895108764f5a49a5 Mon Sep 17 00:00:00 2001
From: AnyOldName3 <krizdjali@gmail.com>
Date: Mon, 7 Oct 2024 18:49:01 +0100
Subject: [PATCH] Win32 interactive resizing proof-of-concept

Basically works by setting up a callback to draw a new frame which we do when the WM_PAINT event arrives, which is how Windows tries to tell us it's time to redraw the window due to a resize etc.

Unlike the WM_SIZE event, it only happens when we've consumed the whole message queue, so it should be pretty similar to the regular situation where a frame happens after `pollEvents` is called.

This approach is necessary in the first place because Win32 window messages can be reentrant, so the handler for one event, like a click on the corner of a window, can in turn fire a series of extra messages for the drag and resizes and release, without first returning.
---
 include/vsg/app/Viewer.h                |  3 +++
 include/vsg/app/Window.h                |  2 ++
 src/vsg/app/Viewer.cpp                  | 25 +++++++++++++++++++++++++
 src/vsg/platform/win32/Win32_Window.cpp |  2 ++
 4 files changed, 32 insertions(+)

diff --git a/include/vsg/app/Viewer.h b/include/vsg/app/Viewer.h
index 880f0ee5c6..145e6e074f 100644
--- a/include/vsg/app/Viewer.h
+++ b/include/vsg/app/Viewer.h
@@ -101,6 +101,9 @@ namespace vsg
         /// If still active, poll for pending events and place them in the Events list and advance to the next frame, generate updated FrameStamp to signify the advancement to a new frame and return true.
         virtual bool advanceToNextFrame(double simulationTime = UseTimeSinceStartPoint);
 
+        virtual bool advanceToNextFramePhaseOne();
+        virtual bool advanceToNextFramePhaseTwo(double simulationTime = UseTimeSinceStartPoint);
+
         /// pass the Events into any registered EventHandlers
         virtual void handleEvents();
 
diff --git a/include/vsg/app/Window.h b/include/vsg/app/Window.h
index d1b475d251..e89f478c17 100644
--- a/include/vsg/app/Window.h
+++ b/include/vsg/app/Window.h
@@ -58,6 +58,8 @@ namespace vsg
 
         virtual void resize() {}
 
+        std::function<void()> resizeCallback = {};
+
         ref_ptr<WindowTraits> traits() { return _traits; }
         const ref_ptr<WindowTraits> traits() const { return _traits; }
 
diff --git a/src/vsg/app/Viewer.cpp b/src/vsg/app/Viewer.cpp
index d15ce5dba1..3dceb0e239 100644
--- a/src/vsg/app/Viewer.cpp
+++ b/src/vsg/app/Viewer.cpp
@@ -79,6 +79,14 @@ void Viewer::addWindow(ref_ptr<Window> window)
     if (itr != _windows.end()) return;
 
     _windows.push_back(window);
+
+    window->resizeCallback = [this]() {
+        advanceToNextFramePhaseTwo();
+        handleEvents();
+        update();
+        recordAndSubmit();
+        present();
+    };
 }
 
 void Viewer::removeWindow(ref_ptr<Window> window)
@@ -88,6 +96,8 @@ void Viewer::removeWindow(ref_ptr<Window> window)
 
     _windows.erase(itr);
 
+    window->resizeCallback = nullptr;
+
     // create a new list of CommandGraphs not associated with removed window
     CommandGraphs commandGraphs;
     for (const auto& task : recordAndSubmitTasks)
@@ -153,6 +163,14 @@ bool Viewer::pollEvents(bool discardPreviousEvents)
 }
 
 bool Viewer::advanceToNextFrame(double simulationTime)
+{
+    if (!advanceToNextFramePhaseOne())
+        return false;
+
+    return advanceToNextFramePhaseTwo(simulationTime);
+}
+
+bool vsg::Viewer::advanceToNextFramePhaseOne()
 {
     static constexpr SourceLocation s_frame_source_location{"Viewer advanceToNextFrame", VsgFunctionName, __FILE__, __LINE__, COLOR_VIEWER, 1};
 
@@ -167,6 +185,13 @@ bool Viewer::advanceToNextFrame(double simulationTime)
     // poll all the windows for events.
     pollEvents(true);
 
+    return true;
+}
+
+bool vsg::Viewer::advanceToNextFramePhaseTwo(double simulationTime)
+{
+    static constexpr SourceLocation s_frame_source_location{"Viewer advanceToNextFrame", VsgFunctionName, __FILE__, __LINE__, COLOR_VIEWER, 1};
+
     if (!acquireNextFrame()) return false;
 
     // create FrameStamp for frame
diff --git a/src/vsg/platform/win32/Win32_Window.cpp b/src/vsg/platform/win32/Win32_Window.cpp
index fe1a05248e..4a7081c3f3 100644
--- a/src/vsg/platform/win32/Win32_Window.cpp
+++ b/src/vsg/platform/win32/Win32_Window.cpp
@@ -610,6 +610,8 @@ bool Win32_Window::handleWin32Messages(UINT msg, WPARAM wParam, LPARAM lParam)
         _windowMapped = false;
         return true;
     case WM_PAINT:
+        if (resizeCallback)
+            resizeCallback();
         ValidateRect(_window, NULL);
         return true;
     case WM_MOUSEMOVE: {