drag scroll

Author: wkjarosz

include/imgui_ext.h

@@ -1,4 +1,5 @@
 #include "imgui.h"
+#include "imgui_internal.h"
 
 namespace ImGui
 {
@@ -38,4 +39,24 @@ inline bool MenuItem(const string &label, const string &shortcut, bool *p_select
     return MenuItem(label.c_str(), shortcut.c_str(), p_selected, enabled);
 }
 
+// from https://github.com/ocornut/imgui/issues/3379#issuecomment-1678718752
+void ScrollWhenDraggingOnVoid(const ImVec2 &delta, ImGuiMouseButton mouse_button)
+{
+    ImGuiContext &g       = *ImGui::GetCurrentContext();
+    ImGuiWindow  *window  = g.CurrentWindow;
+    bool          hovered = false;
+    bool          held    = false;
+    ImGuiID       id      = window->GetID("##scrolldraggingoverlay");
+    ImGui::KeepAliveID(id);
+    ImGuiButtonFlags button_flags = (mouse_button == 0)   ? ImGuiButtonFlags_MouseButtonLeft
+                                    : (mouse_button == 1) ? ImGuiButtonFlags_MouseButtonRight
+                                                          : ImGuiButtonFlags_MouseButtonMiddle;
+    if (g.HoveredId == 0) // If nothing hovered so far in the frame (not same as IsAnyItemHovered()!)
+        ImGui::ButtonBehavior(window->Rect(), id, &hovered, &held, button_flags);
+    if (held && delta.x != 0.0f)
+        ImGui::SetScrollX(window, window->Scroll.x + delta.x);
+    if (held && delta.y != 0.0f)
+        ImGui::SetScrollY(window, window->Scroll.y + delta.y);
+}
+
 } // namespace ImGui

src/app.cpp

@@ -646,6 +646,7 @@ void SampleViewer::draw_about_dialog()
         }
         // ImGui::SetItemDefaultFocus();
 
+        ImGui::ScrollWhenDraggingOnVoid(ImVec2(0.0f, -ImGui::GetIO().MouseDelta.y), ImGuiMouseButton_Left);
         ImGui::EndPopup();
         g_open_help = false;
     }
@@ -963,6 +964,7 @@ void SampleViewer::draw_editor()
         ImGui::Dummy({0, HelloImGui::EmSize(0.25f)});
     }
     ImGui::PopItemWidth();
+    ImGui::ScrollWhenDraggingOnVoid(ImVec2(0.0f, -ImGui::GetIO().MouseDelta.y), ImGuiMouseButton_Left);
 }
 
 bool SampleViewer::process_event(void *e)