Viewport: Fixed mouse hover flicker on mouse button release frame after moving a window. (#1542)

Platform: Clarifying some comments in back-ends.

TODO.txt

@@ -262,6 +262,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - viewport: platform: introduce getfocus/setfocus api, so e.g. focus flags can be honored, imgui-side ctrl-tab can focus os window, OS alt-tab can focus imgui window etc.
  - viewport: store per-viewport/monitor DPI in .ini file so an application reload or main window changing DPI on reload can be properly patched for.
  - viewport: vulkan renderer implementation. 
+ - viewport: fallback calculation of hovered window is very currently wrong without ImGuiBackendFlags_HasMouseHoveredViewport. typically affect half-overlapping viewported menus. 
  - viewport: need to clarify how to use GetMousePos() from a user point of view.
 
  - inputs: we need an explicit flag about whether the imgui window is focused, to be able to distinguish focused key releases vs alt-tabbing all release behaviors.

examples/imgui_impl_dx10.cpp

@@ -504,7 +504,9 @@ void ImGui_ImplDX10_NewFrame()
 }
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Interface (Optional, for multi-viewport support)
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
 //--------------------------------------------------------------------------------------------------------
 
 struct ImGuiViewportDataDx10
@@ -581,11 +583,7 @@ static void ImGui_ImplDX10_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)
         ID3D10Texture2D* pBackBuffer = NULL;
         data->SwapChain->ResizeBuffers(0, (UINT)size.x, (UINT)size.y, DXGI_FORMAT_UNKNOWN, 0);
         data->SwapChain->GetBuffer(0, IID_PPV_ARGS(&pBackBuffer));
-        if (pBackBuffer == NULL)
-        {
-            fprintf(stderr, "ImGui_ImplDX10_SetWindowSize() can't created buffers.\n");
-            return;
-        }
+        if (pBackBuffer == NULL) { fprintf(stderr, "ImGui_ImplDX10_SetWindowSize() failed creating buffers.\n"); return; }
         g_pd3dDevice->CreateRenderTargetView(pBackBuffer, NULL, &data->RTView);
         pBackBuffer->Release();
     }

examples/imgui_impl_dx11.cpp

@@ -512,7 +512,9 @@ void ImGui_ImplDX11_NewFrame()
 }
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Interface (Optional, for multi-viewport support)
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
 //--------------------------------------------------------------------------------------------------------
 
 struct ImGuiViewportDataDx11
@@ -589,11 +591,7 @@ static void ImGui_ImplDX11_SetWindowSize(ImGuiViewport* viewport, ImVec2 size)
         ID3D11Texture2D* pBackBuffer = NULL;
         data->SwapChain->ResizeBuffers(0, (UINT)size.x, (UINT)size.y, DXGI_FORMAT_UNKNOWN, 0);
         data->SwapChain->GetBuffer(0, IID_PPV_ARGS(&pBackBuffer));
-        if (pBackBuffer == NULL)
-        {
-            fprintf(stderr, "ImGui_ImplDX11_SetWindowSize() can't created buffers.\n");
-            return;
-        }
+        if (pBackBuffer == NULL) { fprintf(stderr, "ImGui_ImplDX11_SetWindowSize() failed creating buffers.\n"); return; }
         g_pd3dDevice->CreateRenderTargetView(pBackBuffer, NULL, &data->RTView);
         pBackBuffer->Release();
     }

examples/imgui_impl_dx12.cpp

@@ -637,7 +637,9 @@ void ImGui_ImplDX12_NewFrame(ID3D12GraphicsCommandList* command_list)
 }
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Interface (Optional, for multi-viewport support)
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
 //--------------------------------------------------------------------------------------------------------
 
 struct ImGuiViewportDataDx12

examples/imgui_impl_glfw.cpp

@@ -317,9 +317,11 @@ void ImGui_ImplGlfw_NewFrame()
     ImGui::NewFrame();
 }
 
-// --------------------------------------------------------------------------------------------------------
-// Platform Windows
-// --------------------------------------------------------------------------------------------------------
+//--------------------------------------------------------------------------------------------------------
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
+//--------------------------------------------------------------------------------------------------------
 
 struct ImGuiViewportDataGlfw
 {

examples/imgui_impl_opengl2.cpp

@@ -211,7 +211,9 @@ void    ImGui_ImplOpenGL2_DestroyDeviceObjects()
 }
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Interface (Optional, for multi-viewport support)
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
 //--------------------------------------------------------------------------------------------------------
 
 static void ImGui_ImplOpenGL2_RenderWindow(ImGuiViewport* viewport, void*)

examples/imgui_impl_opengl3.cpp

@@ -330,7 +330,9 @@ void    ImGui_ImplOpenGL3_DestroyDeviceObjects()
 }
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Interface (Optional, for multi-viewport support)
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
 //--------------------------------------------------------------------------------------------------------
 
 static void ImGui_ImplOpenGL3_RenderWindow(ImGuiViewport* viewport, void*)

examples/imgui_impl_sdl2.cpp

@@ -276,7 +276,9 @@ void ImGui_ImplSDL2_NewFrame(SDL_Window* window)
 }
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Interface (Optional, for multi-viewport support)
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
 //--------------------------------------------------------------------------------------------------------
 
 struct ImGuiViewportDataSDL2

examples/imgui_impl_vulkan.cpp

@@ -1059,7 +1059,10 @@ void ImGui_ImplVulkanH_DestroyWindowData(VkInstance instance, VkDevice device, I
 }
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Interface (Optional, for multi-viewport support)
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
+//--------------------------------------------------------------------------------------------------------
 // FIXME-PLATFORM: Vulkan support unfinished
 //--------------------------------------------------------------------------------------------------------
 

examples/imgui_impl_win32.cpp

@@ -390,7 +390,9 @@ static void ImGui_ImplWin32_SetImeInputPos(ImGuiViewport* viewport, ImVec2 pos)
 #endif
 
 //--------------------------------------------------------------------------------------------------------
-// Platform Windows
+// MULTI-VIEWPORT / PLATFORM INTERFACE SUPPORT
+// This is an _advanced_ and _optional_ feature, allowing the back-end to create and handle multiple viewports simultaneously.
+// If you are new to dear imgui or creating a new binding for dear imgui, it is recommended that you completely ignore this section first..
 //--------------------------------------------------------------------------------------------------------
 
 struct ImGuiViewportDataWin32

imgui.cpp

@@ -3357,7 +3357,11 @@ static void ImGui::UpdateMovingWindow()
         {
             UpdateTryMergeWindowIntoHostViewport(moving_window, g.MouseRefViewport);
 
-            // Clear the NoInput flag set by the Viewport system
+            // Patch the mouse viewport so that we don't hover under the moved window during the mouse released frame
+            if (!IsDragDropPayloadBeingAccepted())
+                g.MouseRefViewport = moving_window->Viewport;
+
+            // Clear the NoInput window flag set by the Viewport system
             moving_window->Viewport->Flags &= ~ImGuiViewportFlags_NoInputs;
 
             ClearActiveID();