I6839 fix multi viewport window position (#5448)

* fix search free position for window

* fix blink window position

* fix and test

* update

* update

* fixes

* small fixes, added comments

---------

Co-authored-by: Grant Karapetyan <grant.karapetyan@meshinspector.com>

Author: ABSitf

source/MRViewer/ImGuiMenu.cpp

@@ -293,8 +293,28 @@ void ImGuiMenu::startFrame()
             style.Colors[ImGuiCol_ModalWindowDimBg] = ImVec4( 0.9f, 0.9f, 0.9f, 0.5f );
 
     }
+
+    // checking for mouse or keyboard events
+    // this will start drawing multiple frames without a swapping to render the interface elements without flickering
+    bool needIncrement = false;
+    if ( ImGui::GetIO().ConfigFlags & ImGuiConfigFlags_ViewportsEnable && context_ )
+    {
+        if ( !context_->InputEventsQueue.empty() )
+        {
+            needIncrement = context_->InputEventsQueue.back().Type == ImGuiInputEventType_MouseButton ||
+                context_->InputEventsQueue.back().Type == ImGuiInputEventType_MouseWheel ||
+                context_->InputEventsQueue.back().Type == ImGuiInputEventType_Key;
+        }
+    }
+
     ImGui::NewFrame();
     UI::getDefaultWindowRectAllocator().invalidateClosedWindows();
+
+    if ( needIncrement && context_->MouseViewport != ImGui::GetMainViewport() ) // needIncrement can be true only if ImGui::GetIO().ConfigFlags & ImGuiConfigFlags_ViewportsEnable && context_
+    {
+        // drawing multiple frames without a swapping to render the interface elements without flickering
+        viewer->incrementForceRedrawFrames( viewer->forceRedrawMinimumIncrementAfterEvents, true );
+    }
 }
 
 void ImGuiMenu::finishFrame()
@@ -323,7 +343,33 @@ void ImGuiMenu::finishFrame()
         {
             GLFWwindow* backup_current_context = glfwGetCurrentContext();
             ImGui::UpdatePlatformWindows();
-            ImGui::RenderPlatformWindowsDefault();
+
+            if ( context_ )
+            {
+                for ( int i = 1; i < context_->Viewports.Size; ++i )
+                {
+                    const auto* vp = context_->Viewports[i];
+                    // if non-main viewport will be deleted in following frames we force redraw of main frame
+                    // to ensure that there is at least one frame when both removed viewport and main viewport renders the window
+                    if ( vp->LastFrameActive < context_->FrameCount )
+                    {
+                        viewer->forceSwapOnFrame();
+                        break;
+                    }
+                }
+
+                if ( viewer->isCurrentFrameSwapping() )
+                {
+                    ImGui::RenderPlatformWindowsDefault();
+
+                    // if in swapping frame new viewport appears deffer swapping for main viewport for one frame
+                    // to ensure that there is at least one frame when both new viewport and main viewport renders the window
+                    static int prevViewports = context_->Viewports.Size;
+                    if ( context_->Viewports.Size > prevViewports )
+                        viewer->incrementForceRedrawFrames( 1, true );
+                    prevViewports = context_->Viewports.Size;
+                }
+            }
             glfwMakeContextCurrent( backup_current_context );
         }
     }

source/MRViewer/MRUIRectAllocator.cpp

@@ -158,22 +158,50 @@ void WindowRectAllocator::setFreeNextWindowPos( const char* expectedWindowName,
 
     if ( findLocation )
     {
-        // push into application window if it is out
-        const Vector2f appWindowSize = Vector2f( getViewerInstance().framebufferSize );
-        const Box2f appWindowBox = Box2f::fromMinAndSize( ImGuiMV::GetMainViewportShift(), appWindowSize );
         auto windowBox = Box2f::fromMinAndSize( defaultPos, window->Size );
-        defaultPos.x = std::clamp( windowBox.min.x, appWindowBox.min.x, std::max( 0.0f, windowBox.min.x + appWindowBox.min.x - ( windowBox.max.x - appWindowBox.max.x ) ) );
-        defaultPos.y = std::clamp( windowBox.min.y, appWindowBox.min.y, std::max( 0.0f, windowBox.min.y + appWindowBox.min.y - ( windowBox.max.y - appWindowBox.max.y ) ) );
+        Box2f boundsFixed;
+
+        Box2f workBox;
+
+        if ( ImGui::GetIO().ConfigFlags & ImGuiConfigFlags_ViewportsEnable )
+        {
+            const auto& monitors = ImGui::GetPlatformIO().Monitors;
+            for ( const auto& m : monitors )
+            {
+                Box2f mBox = Box2f::fromMinAndSize( m.WorkPos, m.WorkSize );
+                if ( mBox.intersects( windowBox ) ) // alternative way: calculate window area in current monitor
+                {
+                    workBox = mBox;
+                    break;
+                }
+            }
+        }
+        else
+        {
+            const Vector2f appWindowSize = Vector2f( getViewerInstance().framebufferSize );
+            workBox = Box2f::fromMinAndSize( ImGuiMV::GetMainViewportShift(), appWindowSize );
+        }
+        defaultPos.x = std::clamp( windowBox.min.x, workBox.min.x, std::max( 0.0f, workBox.max.x - windowBox.size().x ) );
+        defaultPos.y = std::clamp( windowBox.min.y, workBox.min.y, std::max( 0.0f, workBox.max.y - windowBox.size().y ) );
         windowBox = Box2f::fromMinAndSize( defaultPos, window->Size );
 
-        // convert viewport bounds from local to window space
-        Box2f viewportBounds = getViewerInstance().getViewportsBounds();
-        Box2f boundsFixed = viewportBounds;
-        boundsFixed.min.y = ImGui::GetIO().DisplaySize.y - boundsFixed.max.y;
-        boundsFixed.max.y = boundsFixed.min.y + viewportBounds.size().y;
-        // convert viewport bounds from window to screen space
-        boundsFixed.min = ImGuiMV::Window2ScreenSpaceVector2f( boundsFixed.min );
-        boundsFixed.max = ImGuiMV::Window2ScreenSpaceVector2f( boundsFixed.max );
+
+        if ( ImGui::GetIO().ConfigFlags & ImGuiConfigFlags_ViewportsEnable )
+        {
+            boundsFixed = workBox;
+        }
+        else
+        {
+            // convert viewport bounds from local to window space
+            Box2f viewportBounds = getViewerInstance().getViewportsBounds();
+            boundsFixed = viewportBounds;
+            boundsFixed.min.y = ImGui::GetIO().DisplaySize.y - boundsFixed.max.y;
+            boundsFixed.max.y = boundsFixed.min.y + viewportBounds.size().y;
+            // convert viewport bounds from window to screen space
+            boundsFixed.min = ImGuiMV::Window2ScreenSpaceVector2f( boundsFixed.min );
+            boundsFixed.max = ImGuiMV::Window2ScreenSpaceVector2f( boundsFixed.max );
+        }
+        // push into application window if it is out
 
         auto result = findFreeRect( windowBox, boundsFixed, [&]( Box2f rect, std::function<void( const char*, Box2f )> func )
         {

source/MRViewer/MRViewer.cpp

@@ -2419,9 +2419,14 @@ void Viewer::incrementForceRedrawFrames( int i /*= 1 */, bool swapOnLastOnly /*=
         forceRedrawFramesWithoutSwap_ = std::max( i, forceRedrawFramesWithoutSwap_ );
 }
 
+void Viewer::forceSwapOnFrame( int i /*= 0*/ )
+{
+    forceRedrawFramesWithoutSwap_ = std::min( i, forceRedrawFramesWithoutSwap_ );
+}
+
 bool Viewer::isCurrentFrameSwapping() const
 {
-    return forceRedrawFramesWithoutSwap_ == 0;
+    return forceRedrawFramesWithoutSwap_ <= 1;
 }
 
 size_t Viewer::getEventsCount( EventType type ) const

source/MRViewer/MRViewer.h

@@ -266,6 +266,9 @@ class MRVIEWER_CLASS Viewer
     // if `swapOnLastOnly` only last forced frame will be present on screen and all previous will not
     MRVIEWER_API void incrementForceRedrawFrames( int i = 1, bool swapOnLastOnly = false );
 
+    // Forces redraw no later than the specified number of frames
+    MRVIEWER_API void forceSwapOnFrame( int i = 0 );
+
     // Returns true if current frame will be shown on display
     MRVIEWER_API bool isCurrentFrameSwapping() const;