Viewport, Platform: Refresh monitor list (win32, glfw) + avoid calling GetWindowFocus before platform window creation to not require of backend to null-check things inconsistently. (#1542)

TODO.txt

@@ -262,6 +262,9 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - 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: need to clarify how to use GetMousePos() from a user point of view.
+ - platform: glfw: no support for ImGuiBackendFlags_HasMouseHoveredViewport. 
+ - platform: sdl: no support for ImGuiBackendFlags_HasMouseHoveredViewport. maybe we could use SDL_GetMouseFocus() / SDL_WINDOW_MOUSE_FOCUS if imgui could fallback on its heuristic when NoInputs is set
+ - platform: sdl: no refresh of monitor/display (SDL doesn't seem to have an event for it).
 
  - 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.
  - inputs: rework IO system to be able to pass actual ordered/timestamped events. use an event queue? (~#335, #71)

examples/imgui_impl_glfw.cpp

@@ -53,10 +53,12 @@ static GlfwClientApi    g_ClientApi = GlfwClientApi_Unknown;
 static double           g_Time = 0.0f;
 static bool             g_MouseJustPressed[5] = { false, false, false, false, false };
 static GLFWcursor*      g_MouseCursors[ImGuiMouseCursor_Count_] = { 0 };
+static bool             g_WantUpdateMonitors = true;
 
 // Forward Declarations
 static void ImGui_ImplGlfw_InitPlatformInterface();
 static void ImGui_ImplGlfw_ShutdownPlatformInterface();
+static void ImGui_ImplGlfw_UpdateMonitors();
 
 static const char* ImGui_ImplGlfw_GetClipboardText(void* user_data)
 {
@@ -271,6 +273,8 @@ void ImGui_ImplGlfw_NewFrame()
     glfwGetFramebufferSize(g_Window, &display_w, &display_h);
     io.DisplaySize = ImVec2((float)w, (float)h);
     io.DisplayFramebufferScale = ImVec2(w > 0 ? ((float)display_w / w) : 0, h > 0 ? ((float)display_h / h) : 0);
+    if (g_WantUpdateMonitors)
+        ImGui_ImplGlfw_UpdateMonitors();
 
     // Setup time step
     double current_time = glfwGetTime();
@@ -562,7 +566,6 @@ static int ImGui_ImplGlfw_CreateVkSurface(ImGuiViewport* viewport, ImU64 vk_inst
 }
 #endif // GLFW_HAS_VULKAN
 
-// FIXME-PLATFORM: Update monitor list when changed (using glfwSetMonitorCallback?)
 // FIXME-PLATFORM: GLFW doesn't export monitor work area (see https://github.com/glfw/glfw/pull/989)
 static void ImGui_ImplGlfw_UpdateMonitors()
 {
@@ -586,6 +589,12 @@ static void ImGui_ImplGlfw_UpdateMonitors()
 #endif
         platform_io.Monitors.push_back(monitor);
     }
+    g_WantUpdateMonitors = false;
+}
+
+static void ImGui_ImplGlfw_MonitorCallback(GLFWmonitor*, int)
+{
+    g_WantUpdateMonitors = true;
 }
 
 static void ImGui_ImplGlfw_InitPlatformInterface()
@@ -614,7 +623,9 @@ static void ImGui_ImplGlfw_InitPlatformInterface()
     platform_io.Platform_SetImeInputPos = ImGui_ImplWin32_SetImeInputPos;
 #endif
 
+    // Note: monitor callback are broken GLFW 3.2 and earlier (see github.com/glfw/glfw/issues/784)
     ImGui_ImplGlfw_UpdateMonitors();
+    glfwSetMonitorCallback(ImGui_ImplGlfw_MonitorCallback);
 
     // Register main window handle (which is owned by the main application, not by us)
     ImGuiViewport* main_viewport = ImGui::GetMainViewport();

examples/imgui_impl_sdl2.cpp

@@ -418,8 +418,7 @@ static void ImGui_ImplSDL2_SetWindowFocus(ImGuiViewport* viewport)
 static bool ImGui_ImplSDL2_GetWindowFocus(ImGuiViewport* viewport)
 {
     ImGuiViewportDataSDL2* data = (ImGuiViewportDataSDL2*)viewport->PlatformUserData;
-    bool focus = (SDL_GetWindowFlags(data->Window) & SDL_WINDOW_INPUT_FOCUS) != 0;
-    return focus;
+    return (SDL_GetWindowFlags(data->Window) & SDL_WINDOW_INPUT_FOCUS) != 0;
 }
 
 static void ImGui_ImplSDL2_RenderWindow(ImGuiViewport* viewport, void*)
@@ -452,7 +451,7 @@ static int ImGui_ImplSDL2_CreateVkSurface(ImGuiViewport* viewport, ImU64 vk_inst
 }
 #endif // SDL_HAS_VULKAN
 
-// FIXME-PLATFORM: Update monitor list when changed?
+// FIXME-PLATFORM: SDL doesn't have an event to notify the application of display/monitor changes
 static void ImGui_ImplSDL2_UpdateMonitors()
 {
     ImGuiPlatformIO& platform_io = ImGui::GetPlatformIO();

examples/imgui_impl_win32.cpp

@@ -8,6 +8,7 @@
 #include <tchar.h>
 
 // CHANGELOG
+// (minor and older changes stripped away, please see git history for details)
 //  2018-XX-XX: Platform: Added support for multiple windows via the ImGuiPlatformIO interface.
 //  2018-03-20: Misc: Setup io.BackendFlags ImGuiBackendFlags_HasMouseCursors and ImGuiBackendFlags_HasSetMousePos flags + honor ImGuiConfigFlags_NoMouseCursorChange flag.
 //  2018-02-20: Inputs: Added support for mouse cursors (ImGui::GetMouseCursor() value and WM_SETCURSOR message handling).
@@ -26,10 +27,12 @@ static HWND                 g_hWnd = 0;
 static INT64                g_Time = 0;
 static INT64                g_TicksPerSecond = 0;
 static ImGuiMouseCursor     g_LastMouseCursor = ImGuiMouseCursor_Count_;
+static bool                 g_WantUpdateMonitors = true;
 
 // Forward Declarations
 static void ImGui_ImplWin32_InitPlatformInterface();
 static void ImGui_ImplWin32_ShutdownPlatformInterface();
+static void ImGui_ImplWin32_UpdateMonitors();
 
 // Functions
 bool    ImGui_ImplWin32_Init(void* hwnd)
@@ -159,6 +162,8 @@ void    ImGui_ImplWin32_NewFrame()
     RECT rect;
     ::GetClientRect(g_hWnd, &rect);
     io.DisplaySize = ImVec2((float)(rect.right - rect.left), (float)(rect.bottom - rect.top));
+    if (g_WantUpdateMonitors)
+        ImGui_ImplWin32_UpdateMonitors();
 
     // Setup time step
     INT64 current_time;
@@ -251,7 +256,7 @@ IMGUI_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARAM wPa
         io.MouseWheelH += GET_WHEEL_DELTA_WPARAM(wParam) > 0 ? +1.0f : -1.0f;
         return 0;
     case WM_MOUSEMOVE:
-        io.MousePos.x = (signed short)(lParam);
+        io.MousePos.x = (signed short)(lParam);                 // Note: this is used for single-viewport support, but in reality the code in ImGui_ImplWin32_UpdateMousePos() overwrite this.
         io.MousePos.y = (signed short)(lParam >> 16);
         return 0;
     case WM_KEYDOWN:
@@ -273,6 +278,9 @@ IMGUI_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARAM wPa
         if (LOWORD(lParam) == HTCLIENT && ImGui_ImplWin32_UpdateMouseCursor())
             return 1;
         return 0;
+    case WM_DISPLAYCHANGE:
+        g_WantUpdateMonitors = true;
+        return 0;
     }
     return 0;
 }
@@ -623,11 +631,11 @@ static BOOL CALLBACK ImGui_ImplWin32_UpdateMonitors_EnumFunc(HMONITOR monitor, H
     return TRUE;
 }
 
-// FIXME-PLATFORM: Update monitor list when changed (WM_DISPLAYCHANGE?)
 static void ImGui_ImplWin32_UpdateMonitors()
 {
     ImGui::GetPlatformIO().Monitors.resize(0);
     ::EnumDisplayMonitors(NULL, NULL, ImGui_ImplWin32_UpdateMonitors_EnumFunc, NULL);
+    g_WantUpdateMonitors = false;
 }
 
 static void ImGui_ImplWin32_InitPlatformInterface()

imgui.cpp

@@ -3580,21 +3580,6 @@ void ImGui::UpdatePlatformWindows()
     if (!(g.IO.ConfigFlags & ImGuiConfigFlags_ViewportsEnable))
         return;
 
-    // Update our implicit z-order knowledge of platform windows, which is used when the back-end cannot provide io.MouseHoveredViewport.
-    if (g.PlatformIO.Platform_GetWindowFocus)
-    {
-        ImGuiViewportP* focused_viewport = NULL;
-        for (int i = 0; i < g.Viewports.Size && focused_viewport == NULL; i++)
-            if (g.PlatformIO.Platform_GetWindowFocus(g.Viewports[i]))
-                focused_viewport = g.Viewports[i];
-        if (focused_viewport && g.PlatformLastFocusedViewport != focused_viewport->ID)
-        {
-            if (focused_viewport->LastFrontMostStampCount != g.WindowsFrontMostStampCount)
-                focused_viewport->LastFrontMostStampCount = ++g.WindowsFrontMostStampCount;
-            g.PlatformLastFocusedViewport = focused_viewport->ID;
-        }
-    }
-
     // Create/resize/destroy platform windows to match each active viewport.
     // Skip the main viewport (index 0), which is always fully handled by the application!
     for (int i = 1; i < g.Viewports.Size; i++)
@@ -3631,13 +3616,14 @@ void ImGui::UpdatePlatformWindows()
         }
 
         // Create window
-        bool is_new_window = (viewport->PlatformHandle == NULL && viewport->PlatformUserData == NULL && viewport->RendererUserData == NULL);
-        if (is_new_window && viewport->PlatformHandle == NULL && viewport->PlatformUserData == NULL)
-            g.PlatformIO.Platform_CreateWindow(viewport);
-        if (is_new_window && viewport->RendererUserData == NULL && g.PlatformIO.Renderer_CreateWindow != NULL)
+        bool is_new_window = (viewport->CreatedPlatformWindow == false);
+        if (is_new_window)
         {
-            g.PlatformIO.Renderer_CreateWindow(viewport);
+            g.PlatformIO.Platform_CreateWindow(viewport);
+            if (g.PlatformIO.Renderer_CreateWindow != NULL)
+                g.PlatformIO.Renderer_CreateWindow(viewport);
             viewport->RendererLastSize = viewport->Size;
+            viewport->CreatedPlatformWindow = true;
         }
 
         // Apply Position and Size (from ImGui to Platform/Renderer back-ends)
@@ -3682,6 +3668,22 @@ void ImGui::UpdatePlatformWindows()
         // Clear request flags
         viewport->PlatformRequestClose = viewport->PlatformRequestMove = viewport->PlatformRequestResize = false;
     }
+
+    // Update our implicit z-order knowledge of platform windows, which is used when the back-end cannot provide io.MouseHoveredViewport.
+    if (g.PlatformIO.Platform_GetWindowFocus != NULL)
+    {
+        ImGuiViewportP* focused_viewport = NULL;
+        for (int i = 0; i < g.Viewports.Size && focused_viewport == NULL; i++)
+            if (g.Viewports[i]->PlatformUserData != NULL || g.Viewports[i]->PlatformHandle != NULL || g.Viewports[i]->CreatedPlatformWindow)
+                if (g.PlatformIO.Platform_GetWindowFocus(g.Viewports[i]))
+                    focused_viewport = g.Viewports[i];
+        if (focused_viewport && g.PlatformLastFocusedViewport != focused_viewport->ID)
+        {
+            if (focused_viewport->LastFrontMostStampCount != g.WindowsFrontMostStampCount)
+                focused_viewport->LastFrontMostStampCount = ++g.WindowsFrontMostStampCount;
+            g.PlatformLastFocusedViewport = focused_viewport->ID;
+        }
+    }
 }
 
 // This is a default/basic function for performing the rendering/swap of multiple platform windows.

imgui_internal.h

@@ -515,6 +515,7 @@ struct ImGuiViewportP : public ImGuiViewport
     int                 LastFrontMostStampCount;  // Last stamp number from when a window hosted by this viewport was made front-most (by comparing this value between two viewport we have an implicit viewport z-order
     ImGuiID             LastNameHash;
     ImVec2              LastPos;
+    bool                CreatedPlatformWindow;
     float               Alpha;                    // Window opacity (when dragging dockable windows/viewports we make them transparent)
     float               LastAlpha;
     int                 PlatformMonitor;
@@ -524,7 +525,7 @@ struct ImGuiViewportP : public ImGuiViewport
     ImDrawDataBuilder   DrawDataBuilder;
     ImVec2              RendererLastSize;
 
-    ImGuiViewportP()         { Idx = 1; LastFrameActive = LastFrameOverlayDrawList = LastFrontMostStampCount = -1; LastNameHash = 0; Alpha = LastAlpha = 1.0f; PlatformMonitor = INT_MIN; Window = NULL; OverlayDrawList = NULL; RendererLastSize = ImVec2(-1.0f,-1.0f); }
+    ImGuiViewportP()         { Idx = 1; LastFrameActive = LastFrameOverlayDrawList = LastFrontMostStampCount = -1; LastNameHash = 0; CreatedPlatformWindow = false; Alpha = LastAlpha = 1.0f; PlatformMonitor = INT_MIN; Window = NULL; OverlayDrawList = NULL; RendererLastSize = ImVec2(-1.0f,-1.0f); }
     ~ImGuiViewportP()        { if (OverlayDrawList) IM_DELETE(OverlayDrawList); }
     ImRect  GetRect() const  { return ImRect(Pos.x, Pos.y, Pos.x + Size.x, Pos.y + Size.y); }
     ImVec2  GetCenter() const{ return ImVec2(Pos.x + Size.x * 0.5f, Pos.y + Size.y * 0.5f); }