Viewport: Fixed issue where resize grip would display hovered (before of extruded hit rectangle) while mouse is still off the OS bounds so click would miss it and focus the OS window behind expected one. (#1542)

imgui.cpp

@@ -5398,6 +5398,15 @@ static bool ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
     ImVec2 pos_target(FLT_MAX, FLT_MAX);
     ImVec2 size_target(FLT_MAX, FLT_MAX);
 
+    // Clip mouse interaction rectangles within the viewport (in practice the narrowing is going to happen most of the time).
+    // - Not narrowing would mostly benefit the situation where OS windows _without_ decoration have a threshold for hovering when outside their limits.
+    //   This is however not the case with current back-ends under Win32, but a custom borderless window implementation would benefit from it.
+    // - When decoration are enabled we typically benefit from that distance, but then our resize elements would be conflicting with OS resize elements, so we also narrow.
+    // - Note that we are unable to tell if the platform setup allows hovering with a distance threshold (on Win32, decorated window have such threshold).
+    ImRect clip_viewport_rect(-FLT_MAX, -FLT_MAX, +FLT_MAX, +FLT_MAX);
+    if (!(g.IO.BackendFlags & ImGuiBackendFlags_HasMouseHoveredViewport) || (g.IO.MouseHoveredViewport != window->ViewportId) || !(window->Viewport->Flags & ImGuiViewportFlags_NoDecoration))
+        clip_viewport_rect = window->Viewport->GetRect();
+
     // Resize grips and borders are on layer 1
     window->DC.NavLayerCurrent = ImGuiNavLayer_Menu;
     window->DC.NavLayerCurrentMask = (1 << ImGuiNavLayer_Menu);
@@ -5413,6 +5422,7 @@ static bool ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
         ImRect resize_rect(corner - grip.InnerDir * grip_hover_outer_size, corner + grip.InnerDir * grip_hover_inner_size);
         if (resize_rect.Min.x > resize_rect.Max.x) ImSwap(resize_rect.Min.x, resize_rect.Max.x);
         if (resize_rect.Min.y > resize_rect.Max.y) ImSwap(resize_rect.Min.y, resize_rect.Max.y);
+        resize_rect.ClipWith(clip_viewport_rect);
         bool hovered, held;
         ButtonBehavior(resize_rect, window->GetID((void*)(intptr_t)resize_grip_n), &hovered, &held, ImGuiButtonFlags_FlattenChildren | ImGuiButtonFlags_NoNavFocus);
         //GetForegroundDrawList(window)->AddRect(resize_rect.Min, resize_rect.Max, IM_COL32(255, 255, 0, 255));
@@ -5440,8 +5450,9 @@ static bool ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
     {
         bool hovered, held;
         ImRect border_rect = GetResizeBorderRect(window, border_n, grip_hover_inner_size, WINDOWS_RESIZE_FROM_EDGES_HALF_THICKNESS);
+        border_rect.ClipWith(clip_viewport_rect);
         ButtonBehavior(border_rect, window->GetID((void*)(intptr_t)(border_n + 4)), &hovered, &held, ImGuiButtonFlags_FlattenChildren);
-        //GetForegroundDrawLists(window)->AddRect(border_rect.Min, border_rect.Max, IM_COL32(255, 255, 0, 255));
+        //GetForegroundDrawList(window)->AddRect(border_rect.Min, border_rect.Max, IM_COL32(255, 255, 0, 255));
         if ((hovered && g.HoveredIdTimer > WINDOWS_RESIZE_FROM_EDGES_FEEDBACK_TIMER) || held)
         {
             g.MouseCursor = (border_n & 1) ? ImGuiMouseCursor_ResizeEW : ImGuiMouseCursor_ResizeNS;
@@ -5461,6 +5472,10 @@ static bool ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
     }
     PopID();
 
+    // Resize nav layer
+    window->DC.NavLayerCurrent = ImGuiNavLayer_Main;
+    window->DC.NavLayerCurrentMask = (1 << ImGuiNavLayer_Main);
+
     // Navigation resize (keyboard/gamepad)
     if (g.NavWindowingTarget && g.NavWindowingTarget->RootWindow == window)
     {
@@ -5493,10 +5508,6 @@ static bool ImGui::UpdateManualResize(ImGuiWindow* window, const ImVec2& size_au
         MarkIniSettingsDirty(window);
     }
 
-    // Resize nav layer
-    window->DC.NavLayerCurrent = ImGuiNavLayer_Main;
-    window->DC.NavLayerCurrentMask = (1 << ImGuiNavLayer_Main);
-
     window->Size = window->SizeFull;
     return ret_auto_fit;
 }