Viewport: Fixed not clearing request flags in main viewport, which led some back-end (SDL) to break on resize as PlatformRequestResize would stay true forever and inhibit new sizes passed to AddUpdateViewport(). (#1542)

imgui.cpp

@@ -3818,6 +3818,7 @@ void ImGui::EndFrame()
             IM_ASSERT(viewport->Window != NULL);
         g.PlatformIO.Viewports.push_back(viewport);
     }
+    g.Viewports[0]->ClearRequestFlags(); // Clear main viewport flags because UpdatePlatformWindows() won't do it and may not even be called
 
     // Sort the window list so that all child windows are after their parent
     // We cannot do that on FocusWindow() because childs may not exist yet
@@ -7760,7 +7761,7 @@ void ImGui::UpdatePlatformWindows()
         }
 
         // Clear request flags
-        viewport->PlatformRequestClose = viewport->PlatformRequestMove = viewport->PlatformRequestResize = false;
+        viewport->ClearRequestFlags();
     }
 
     // Update our implicit z-order knowledge of platform windows, which is used when the back-end cannot provide io.MouseHoveredViewport.
@@ -7865,7 +7866,7 @@ void ImGui::DestroyPlatformWindow(ImGuiViewportP* viewport)
     viewport->PlatformHandle = NULL;
     viewport->RendererUserData = viewport->PlatformHandle = NULL;
     viewport->PlatformWindowCreated = false;
-    viewport->PlatformRequestClose = viewport->PlatformRequestMove = viewport->PlatformRequestResize = false;
+    viewport->ClearRequestFlags();
 }
 
 void ImGui::DestroyPlatformWindows()

imgui_internal.h

@@ -675,7 +675,8 @@ struct ImGuiViewportP : public ImGuiViewport
     ImGuiViewportP()            { Idx = -1; LastFrameActive = LastFrameOverlayDrawList = LastFrontMostStampCount = -1; LastNameHash = 0; Alpha = LastAlpha = 1.0f; PlatformMonitor = -1; PlatformWindowCreated = PlatformWindowMinimized = false; Window = NULL; OverlayDrawList = NULL; LastPlatformPos = LastPlatformSize = LastRendererSize = ImVec2(FLT_MAX, FLT_MAX); }
     ~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); }
+    ImVec2  GetCenter() const   { return ImVec2(Pos.x + Size.x * 0.5f, Pos.y + Size.y * 0.5f); }
+    void    ClearRequestFlags() { PlatformRequestClose = PlatformRequestMove = PlatformRequestResize = false; }
 };
 
 struct ImGuiNavMoveResult