Viewport: Removed the need for the back-end to fill io.MousePosViewport, it seems unnecessary at this point. (#1542)

examples/imgui_impl_glfw.cpp

@@ -207,7 +207,6 @@ static void ImGui_ImplGlfw_UpdateMousePosAndButtons()
     ImGuiIO& io = ImGui::GetIO();
     const ImVec2 mouse_pos_backup = io.MousePos;
     io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
-    io.MousePosViewport = 0;
     io.MouseHoveredViewport = 0;
 
     // Update buttons
@@ -236,7 +235,6 @@ static void ImGui_ImplGlfw_UpdateMousePosAndButtons()
                 glfwGetCursorPos(window, &mouse_x, &mouse_y);
                 io.MousePos = ImVec2((float)mouse_x + viewport->Pos.x, (float)mouse_y + viewport->Pos.y);
             }
-            io.MousePosViewport = viewport->ID;
             for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++)
                 io.MouseDown[i] |= glfwGetMouseButton(window, i) != 0;
         }

examples/imgui_impl_sdl.cpp

@@ -233,7 +233,6 @@ static void ImGui_ImplSDL2_UpdateMousePosAndButtons()
     ImGuiIO& io = ImGui::GetIO();
     const ImVec2 mouse_pos_backup = io.MousePos;
     io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
-    io.MousePosViewport = 0;
     io.MouseHoveredViewport = 0;
 
     // Set OS mouse position if requested (rarely used, only when ImGuiConfigFlags_NavEnableSetMousePos is enabled by user)
@@ -268,10 +267,7 @@ static void ImGui_ImplSDL2_UpdateMousePosAndButtons()
         my -= wy;
     }
     if (ImGuiViewport* viewport = ImGui::FindViewportByPlatformHandle((void*)focused_window))
-    {
         io.MousePos = ImVec2(viewport->Pos.x + (float)mx, viewport->Pos.y + (float)my);
-        io.MousePosViewport = viewport->ID;
-    }
 
     // We already retrieve global mouse position, SDL_CaptureMouse() also let the OS know e.g. that our imgui drag outside the SDL window boundaries shouldn't trigger the OS window resize cursor
     // The function is only supported from SDL 2.0.4 (released Jan 2016)

examples/imgui_impl_win32.cpp

@@ -137,8 +137,7 @@ static bool ImGui_ImplWin32_UpdateMouseCursor()
 // B) In Multi-viewport mode imgui needs: (when ImGuiConfigFlags_ViewportsEnable is set)
 //   - io.MousePos ............... mouse position, in OS absolute coordinates (what you'd get from GetCursorPos(), or from WM_MOUSEMOVE+viewport->Pos). 
 //                                 io.MousePos is (0,0) when the mouse is on the upper-left of the primary monitor.
-//   - io.MousePosViewport ....... viewport which mouse position is based from (generally the focused/active/capturing viewport)
-//   - io.MouseHoveredViewport ... [optional] viewport which mouse is hovering, with _very_ specific/strict conditions (Read comments next to io.MouseHoveredViewport. This is _NOT_ easy to provide in many high-level engine because of how we handle the ImGuiViewportFlags_NoInputs flag)
+//   - io.MouseHoveredViewport ... [optional] viewport which mouse is hovering, with _VERY_ specific and strict conditions (Read comments next to io.MouseHoveredViewport. This is _NOT_ easy to provide in many high-level engine because of how we use the ImGuiViewportFlags_NoInputs flag)
 static void ImGui_ImplWin32_UpdateMousePos()
 {
     ImGuiIO& io = ImGui::GetIO();
@@ -154,7 +153,6 @@ static void ImGui_ImplWin32_UpdateMousePos()
     }
 
     io.MousePos = ImVec2(-FLT_MAX, -FLT_MAX);
-    io.MousePosViewport = 0;
     io.MouseHoveredViewport = 0;
 
     // Set mouse position and viewport
@@ -168,7 +166,6 @@ static void ImGui_ImplWin32_UpdateMousePos()
             POINT client_pos = pos;
             ::ScreenToClient(focused_hwnd, &client_pos);
             io.MousePos = ImVec2(viewport->Pos.x + (float)client_pos.x, viewport->Pos.y + (float)client_pos.y);
-            io.MousePosViewport = viewport->ID;
         }
 
     // Our back-end can tell which window is under the mouse cursor (not every back-end can), so pass that info to imgui

imgui.cpp

@@ -3912,13 +3912,15 @@ static void ImGui::UpdateViewports()
     }
     if (viewport_hovered != NULL)
         g.MouseLastHoveredViewport = viewport_hovered;
+    else if (g.MouseLastHoveredViewport == NULL)
+        g.MouseLastHoveredViewport = g.Viewports[0];
 
     // Update mouse reference viewport
     // (when moving a window we aim at its viewport, but this will be overwritten below if we go in drag and drop mode)
     if (g.MovingWindow)
         g.MouseViewport = g.MovingWindow->Viewport; 
     else
-        g.MouseViewport = g.IO.MousePosViewport ? FindViewportByID(g.IO.MousePosViewport) : g.Viewports[0];
+        g.MouseViewport = g.MouseLastHoveredViewport;
 
     // When dragging something, always refer to the last hovered viewport. 
     // - when releasing a moving window we will revert to aiming behind (at viewport_hovered)
@@ -15165,7 +15167,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
             ImGui::Text("NavDisableHighlight: %d, NavDisableMouseHover: %d", g.NavDisableHighlight, g.NavDisableMouseHover);
             ImGui::Text("NavWindowingTarget: '%s'", g.NavWindowingTarget ? g.NavWindowingTarget->Name : "NULL");
             ImGui::Text("DragDrop: %d, SourceId = 0x%08X, Payload \"%s\" (%d bytes)", g.DragDropActive, g.DragDropPayload.SourceId, g.DragDropPayload.DataType, g.DragDropPayload.DataSize);
-            ImGui::Text("MousePosViewport: 0x%08X, Hovered: 0x%08X -> Ref 0x%08X", g.IO.MousePosViewport, g.IO.MouseHoveredViewport, g.MouseViewport->ID);
+            ImGui::Text("MouseViewport: 0x%08X (UserHovered 0x%08X, LastHovered 0x%08X)", g.MouseViewport->ID, g.IO.MouseHoveredViewport, g.MouseLastHoveredViewport->ID);
             ImGui::TreePop();
         }
 

imgui.h

@@ -1144,7 +1144,6 @@ struct ImGuiIO
     bool        MouseDown[5];                   // Mouse buttons: 0=left, 1=right, 2=middle + extras. ImGui itself mostly only uses left button (BeginPopupContext** are using right button). Others buttons allows us to track if the mouse is being used by your application + available to user as a convenience via IsMouse** API.
     float       MouseWheel;                     // Mouse wheel Vertical: 1 unit scrolls about 5 lines text.
     float       MouseWheelH;                    // Mouse wheel Horizontal. Most users don't have a mouse with an horizontal wheel, may not be filled by all back-ends.
-    ImGuiID     MousePosViewport;               // (Optional) When using multiple viewports: viewport from which io.MousePos is based from (when dragging this is generally the captured/focused viewport, even though we can drag outside of it and then it's not hovered anymore). (0 == default viewport)
     ImGuiID     MouseHoveredViewport;           // (Optional) When using multiple viewports: viewport the OS mouse cursor is hovering _IGNORING_ viewports with the ImGuiViewportFlags_NoInputs flag, and _REGARDLESS_ of whether another viewport is focused. Set io.BackendFlags |= ImGuiBackendFlags_HasMouseHoveredViewport if you can provide this info. If you don't imgui will use a decent heuristic instead.
     bool        MouseDrawCursor;                // Request ImGui to draw a mouse cursor for you (if you are on a platform without a mouse cursor).
     bool        KeyCtrl;                        // Keyboard modifier pressed: Control

imgui_demo.cpp

@@ -2133,7 +2133,6 @@ void ImGui::ShowDemoWindow(bool* p_open)
             ImGui::Text("Mouse dbl-clicked:"); for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++) if (ImGui::IsMouseDoubleClicked(i)) { ImGui::SameLine(); ImGui::Text("b%d", i); }
             ImGui::Text("Mouse released:"); for (int i = 0; i < IM_ARRAYSIZE(io.MouseDown); i++) if (ImGui::IsMouseReleased(i))         { ImGui::SameLine(); ImGui::Text("b%d", i); }
             ImGui::Text("Mouse wheel: %.1f", io.MouseWheel);
-            ImGui::Text("Mouse viewport: Ref 0x%08X Hovered 0x%08X", io.MousePosViewport, io.MouseHoveredViewport);
 
             ImGui::Text("Keys down:");      for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (io.KeysDownDuration[i] >= 0.0f)     { ImGui::SameLine(); ImGui::Text("%d (%.02f secs)", i, io.KeysDownDuration[i]); }
             ImGui::Text("Keys pressed:");   for (int i = 0; i < IM_ARRAYSIZE(io.KeysDown); i++) if (ImGui::IsKeyPressed(i))             { ImGui::SameLine(); ImGui::Text("%d", i); }

imgui_internal.h

@@ -701,7 +701,7 @@ struct ImGuiContext
     ImVector<ImGuiViewportP*> Viewports;                        // Active viewports (always 1+, and generally 1 unless multi-viewports are enabled). Each viewports hold their copy of ImDrawData. 
     ImGuiViewportP*         CurrentViewport;                    // We track changes of viewport (happening in Begin) so we can call Platform_OnChangedViewport()
     ImGuiViewportP*         MouseViewport;
-    ImGuiViewportP*         MouseLastHoveredViewport;           // Last known viewport that was hovered by mouse (even if we are not hovering any viewport any more)
+    ImGuiViewportP*         MouseLastHoveredViewport;           // Last known viewport that was hovered by mouse (even if we are not hovering any viewport any more) + honoring the _NoInputs flag.
     ImGuiID                 PlatformLastFocusedViewport;        // Record of last focused platform window/viewport, when this changes we stamp the viewport as front-most
 
     // Navigation data (for gamepad/keyboard)