Docking: Added io.ConfigDockingTransparentPayload option (to use with ImGuiConfigFlags_ViewportsNoMerge)

imgui.cpp

@@ -920,6 +920,9 @@ static const float NAV_WINDOWING_LIST_APPEAR_DELAY          = 0.15f;    // Time
 static const float RESIZE_WINDOWS_FROM_EDGES_HALF_THICKNESS = 4.0f;     // Extend outside and inside windows. Affect FindHoveredWindow().
 static const float RESIZE_WINDOWS_FROM_EDGES_FEEDBACK_TIMER = 0.04f;    // Reduce visual noise by only highlighting the border after a certain time.
 
+// Docking
+static const float DOCKING_TRANSPARENT_PAYLOAD_ALPHA        = 0.50f;    // For use with io.ConfigDockingTransparentPayload. Apply to Viewport _or_ WindowBg in host viewport.
+
 //-------------------------------------------------------------------------
 // [SECTION] FORWARD DECLARATIONS
 //-------------------------------------------------------------------------
@@ -1114,6 +1117,7 @@ ImGuiIO::ImGuiIO()
 
     // Miscellaneous configuration options
     ConfigDockingWithShift = false;
+    ConfigDockingTransparentPayload = false;
 #ifdef __APPLE__
     ConfigMacOSXBehaviors = true;  // Set Mac OS X style defaults based on __APPLE__ compile time flag
 #else
@@ -3281,6 +3285,8 @@ void ImGui::NewFrame()
             IM_ASSERT(g.PlatformIO.Platform_GetWindowSize != NULL  && "Platform init didn't install handlers?");
             IM_ASSERT(g.PlatformIO.Platform_SetWindowSize != NULL  && "Platform init didn't install handlers?");
             IM_ASSERT((g.Viewports[0]->PlatformUserData != NULL || g.Viewports[0]->PlatformHandle != NULL) && "Platform init didn't setup main viewport.");
+            if (g.IO.ConfigDockingTransparentPayload && (g.IO.ConfigFlags & ImGuiConfigFlags_DockingEnable))
+                IM_ASSERT(g.PlatformIO.Platform_SetWindowAlpha != NULL && "Platform_SetWindowAlpha handler is required to use io.ConfigDockingTransparent!");
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
             IM_ASSERT(g.IO.RenderDrawListsFn == NULL);  // Call ImGui::Render() then pass ImGui::GetDrawData() yourself to your render function!
 #endif
@@ -5367,13 +5373,29 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             // Window background
             if (!(flags & ImGuiWindowFlags_NoBackground))
             {
+                bool is_docking_transparent_payload = false;
+                if (g.DragDropActive && (g.FrameCount - g.DragDropAcceptFrameCount) <= 1 && g.IO.ConfigDockingTransparentPayload)
+                    if (g.DragDropPayload.IsDataType(IMGUI_PAYLOAD_TYPE_WINDOW) && *(ImGuiWindow**)g.DragDropPayload.Data == window)
+                        is_docking_transparent_payload = true;
+
                 ImU32 bg_col = GetColorU32(GetWindowBgColorIdxFromFlags(flags));
-                if (g.NextWindowData.BgAlphaCond != 0)
-                    bg_col = (bg_col & ~IM_COL32_A_MASK) | (IM_F32_TO_INT8_SAT(g.NextWindowData.BgAlphaVal) << IM_COL32_A_SHIFT);
                 if (window->ViewportOwned)
                 {
-                    //window->Viewport->Alpha = ((bg_col & IM_COL32_A_MASK) >> IM_COL32_A_SHIFT) / 255.0f;
+                    // No alpha
                     bg_col = (bg_col | IM_COL32_A_MASK);
+                    if (is_docking_transparent_payload)
+                        window->Viewport->Alpha *= DOCKING_TRANSPARENT_PAYLOAD_ALPHA;
+                }
+                else
+                {
+                    // Adjust alpha. For docking
+                    float alpha = 1.0f;
+                    if (g.NextWindowData.BgAlphaCond != 0)
+                        alpha = g.NextWindowData.BgAlphaVal;
+                    if (is_docking_transparent_payload)
+                        alpha *= DOCKING_TRANSPARENT_PAYLOAD_ALPHA;
+                    if (alpha != 1.0f)
+                        bg_col = (bg_col & ~IM_COL32_A_MASK) | (IM_F32_TO_INT8_SAT(alpha) << IM_COL32_A_SHIFT);
                 }
                 window->DrawList->AddRectFilled(window->Pos + ImVec2(0, window->TitleBarHeight()), window->Pos + window->Size, bg_col, window_rounding, (flags & ImGuiWindowFlags_NoTitleBar) ? ImDrawCornerFlags_All : ImDrawCornerFlags_Bot);
             }
@@ -7534,7 +7556,7 @@ static void ImGui::UpdateViewports()
             if (g.PlatformIO.Platform_GetWindowMinimized && (n == 0 || viewport->CreatedPlatformWindow))
                 viewport->PlatformIsMinimized = g.PlatformIO.Platform_GetWindowMinimized(viewport);
 
-            // Apply Position and Size (from Platform Window to ImGui) if requested. 
+            // Update Position and Size (from Platform Window to ImGui) if requested. 
             // We do it early in the frame instead of waiting for UpdatePlatformWindows() to avoid a frame of lag when moving/resizing using OS facilities.
             if (!viewport->PlatformIsMinimized)
             {
@@ -7548,6 +7570,9 @@ static void ImGui::UpdateViewports()
             viewport->PlatformMonitor = FindPlatformMonitorForRect(viewport->GetRect());
         }
 
+        // Reset alpha every frame. Users of transparency (docking) needs to request a lower alpha back.
+        viewport->Alpha = 1.0f;
+
         // Translate imgui windows when a Host Viewport has been moved
         // (This additionally keeps windows at the same place when ImGuiConfigFlags_ViewportsEnable is toggled!)
         ImVec2 viewport_delta = viewport->Pos - viewport->LastPos;
@@ -11352,19 +11377,23 @@ static void ImGui::DockNodePreviewDockRender(ImGuiWindow* host_window, ImGuiDock
 {
     ImGuiContext& g = *GImGui;
 
+    // With this option, we only display the preview on the target viewport, and the payload viewport is made transparent.
+    // To compensate for the single layer obstructed by the payload, we'll increase the alpha of the preview nodes.
+    const bool is_transparent_payload = g.IO.ConfigDockingTransparentPayload;
+
     // In case the two windows involved are on different viewports, we will draw the overlay on each of them.
     int overlay_draw_lists_count = 0;
     ImDrawList* overlay_draw_lists[2];
     overlay_draw_lists[overlay_draw_lists_count++] = GetOverlayDrawList(host_window->Viewport);
-    if (host_window->Viewport != root_payload->Viewport)
+    if (host_window->Viewport != root_payload->Viewport && !is_transparent_payload)
         overlay_draw_lists[overlay_draw_lists_count++] = GetOverlayDrawList(root_payload->Viewport);
 
     // Draw main preview rectangle
     const ImU32 overlay_col_tabs = GetColorU32(ImGuiCol_TabActive);
-    const ImU32 overlay_col_main = GetColorU32(ImGuiCol_DockingPreview, 0.40f);
-    const ImU32 overlay_col_drop = GetColorU32(ImGuiCol_DockingPreview, 0.70f);
-    const ImU32 overlay_col_drop_hovered = GetColorU32(ImGuiCol_DockingPreview);
-    const ImU32 overlay_col_lines = GetColorU32(ImGuiCol_NavWindowingHighlight, 0.60f);
+    const ImU32 overlay_col_main = GetColorU32(ImGuiCol_DockingPreview, is_transparent_payload ? 0.60f : 0.40f);
+    const ImU32 overlay_col_drop = GetColorU32(ImGuiCol_DockingPreview, is_transparent_payload ? 0.90f : 0.70f);
+    const ImU32 overlay_col_drop_hovered = GetColorU32(ImGuiCol_DockingPreview, is_transparent_payload ? 1.20f : 1.00f);
+    const ImU32 overlay_col_lines = GetColorU32(ImGuiCol_NavWindowingHighlight, is_transparent_payload ? 0.80f : 0.60f);
 
     // Display area preview
     const bool can_preview_tabs = (root_payload->DockNodeAsHost == NULL || root_payload->DockNodeAsHost->Windows.Size > 0);

imgui.h

@@ -1277,6 +1277,7 @@ struct ImGuiIO
     // Miscellaneous configuration options
     bool          MouseDrawCursor;                  // = false      // Request ImGui to draw a mouse cursor for you (if you are on a platform without a mouse cursor). Cannot be easily renamed to 'io.ConfigXXX' because this is frequently used by back-end implementations.
     bool          ConfigDockingWithShift;           // = false      // Enable docking with holding Shift key (reduce visual noise, allows dropping in wider space)
+    bool          ConfigDockingTransparentPayload;  // = false      // [BETA] Make window or viewport transparent when docking and only display docking boxes on the target viewport. Useful if rendering of multiple viewport can be synced. Best used with ImGuiConfigFlags_ViewportsNoMerge.
     bool          ConfigMacOSXBehaviors;            // = defined(__APPLE__) // OS X style: Text editing cursor movement using Alt instead of Ctrl, Shortcuts using Cmd/Super instead of Ctrl, Line/Text Start and End using Cmd+Arrows instead of Home/End, Double click selects by word instead of selecting whole text, Multi-selection in lists uses Cmd/Super instead of Ctrl (was called io.OptMacOSXBehaviors prior to 1.63)
     bool          ConfigInputTextCursorBlink;       // = true       // Set to false to disable blinking cursor, for users who consider it distracting. (was called: io.OptCursorBlink prior to 1.63)
     bool          ConfigResizeWindowsFromEdges;     // = true       // [BETA] Enable resizing of windows from their edges and from the lower-left corner. This requires (io.BackendFlags & ImGuiBackendFlags_HasMouseCursors) because it needs mouse cursor feedback. (This used to be the ImGuiWindowFlags_ResizeFromAnySide flag)

imgui_internal.h

@@ -1490,6 +1490,7 @@ namespace ImGui
     inline bool             IsNavInputPressedAnyOfTwo(ImGuiNavInput n1, ImGuiNavInput n2, ImGuiInputReadMode mode) { return (GetNavInputAmount(n1, mode) + GetNavInputAmount(n2, mode)) > 0.0f; }
     
     // Docking
+    // (some functions are only declared in imgui.cpp, see Docking section)
     IMGUI_API void          DockContextInitialize(ImGuiContext* ctx);
     IMGUI_API void          DockContextShutdown(ImGuiContext* ctx);
     IMGUI_API void          DockContextOnLoadSettings(ImGuiContext* ctx);