GetMouseDragDelta(): also returns the delta on the mouse button released frame. Verify that mouse positions are valid otherwise returns zero. Removed obsolete comment. Tweaked demo. (#2419)

docs/CHANGELOG.txt

@@ -36,6 +36,8 @@ HOW TO UPDATE?
 Breaking Changes:
 
 Other Changes:
+- GetMouseDragDelta(): also returns the delta on the mouse button released frame. (#2419)
+- GetMouseDragDelta(): verify that mouse positions are valid otherwise returns zero.
 - Examples: OpenGL: Added a dummy GL call + comments in ImGui_ImplOpenGL3_Init() to detect uninitialized
   GL function loaders early, and help users understand what they are missing. (#2421)
 

imgui.cpp

@@ -4206,7 +4206,7 @@ bool ImGui::IsMousePosValid(const ImVec2* mouse_pos)
     return p.x >= MOUSE_INVALID && p.y >= MOUSE_INVALID;
 }
 
-// Return the delta from the initial clicking position.
+// Return the delta from the initial clicking position while the mouse button is clicked or was just released.
 // This is locked and return 0.0f until the mouse moves past a distance threshold at least once.
 // NB: This is only valid if IsMousePosValid(). Back-ends in theory should always keep mouse position valid when dragging even outside the client window.
 ImVec2 ImGui::GetMouseDragDelta(int button, float lock_threshold)
@@ -4215,9 +4215,10 @@ ImVec2 ImGui::GetMouseDragDelta(int button, float lock_threshold)
     IM_ASSERT(button >= 0 && button < IM_ARRAYSIZE(g.IO.MouseDown));
     if (lock_threshold < 0.0f)
         lock_threshold = g.IO.MouseDragThreshold;
-    if (g.IO.MouseDown[button])
+    if (g.IO.MouseDown[button] || g.IO.MouseReleased[button])
         if (g.IO.MouseDragMaxDistanceSqr[button] >= lock_threshold * lock_threshold)
-            return g.IO.MousePos - g.IO.MouseClickedPos[button];     // Assume we can only get active with left-mouse button (at the moment).
+            if (IsMousePosValid(&g.IO.MousePos) && IsMousePosValid(&g.IO.MouseClickedPos[button]))
+                return g.IO.MousePos - g.IO.MouseClickedPos[button];
     return ImVec2(0.0f, 0.0f);
 }
 

imgui.h

@@ -662,7 +662,7 @@ namespace ImGui
     IMGUI_API bool          IsMousePosValid(const ImVec2* mouse_pos = NULL);                    // by convention we use (-FLT_MAX,-FLT_MAX) to denote that there is no mouse
     IMGUI_API ImVec2        GetMousePos();                                                      // shortcut to ImGui::GetIO().MousePos provided by user, to be consistent with other calls
     IMGUI_API ImVec2        GetMousePosOnOpeningCurrentPopup();                                 // retrieve backup of mouse position at the time of opening popup we have BeginPopup() into
-    IMGUI_API ImVec2        GetMouseDragDelta(int button = 0, float lock_threshold = -1.0f);    // return the delta from the initial clicking position. This is locked and return 0.0f until the mouse moves past a distance threshold at least once. If lock_threshold < -1.0f uses io.MouseDraggingThreshold
+    IMGUI_API ImVec2        GetMouseDragDelta(int button = 0, float lock_threshold = -1.0f);    // return the delta from the initial clicking position while the mouse button is pressed or was just released. This is locked and return 0.0f until the mouse moves past a distance threshold at least once. If lock_threshold < -1.0f uses io.MouseDraggingThreshold.
     IMGUI_API void          ResetMouseDragDelta(int button = 0);                                //
     IMGUI_API ImGuiMouseCursor GetMouseCursor();                                                // get desired cursor type, reset in ImGui::NewFrame(), this is updated during the frame. valid before Render(). If you use software rendering by setting io.MouseDrawCursor ImGui will render those for you
     IMGUI_API void          SetMouseCursor(ImGuiMouseCursor type);                              // set desired cursor type

imgui_demo.cpp

@@ -2646,22 +2646,17 @@ static void ShowDemoWindowMisc()
             for (int button = 0; button < 3; button++)
                 ImGui::Text("IsMouseDragging(%d):\n  w/ default threshold: %d,\n  w/ zero threshold: %d\n  w/ large threshold: %d",
                     button, ImGui::IsMouseDragging(button), ImGui::IsMouseDragging(button, 0.0f), ImGui::IsMouseDragging(button, 20.0f));
+        
             ImGui::Button("Drag Me");
             if (ImGui::IsItemActive())
-            {
-                // Draw a line between the button and the mouse cursor
-                ImDrawList* draw_list = ImGui::GetWindowDrawList();
-                draw_list->PushClipRectFullScreen();
-                draw_list->AddLine(io.MouseClickedPos[0], io.MousePos, ImGui::GetColorU32(ImGuiCol_Button), 4.0f);
-                draw_list->PopClipRect();
-
-                // Drag operations gets "unlocked" when the mouse has moved past a certain threshold (the default threshold is stored in io.MouseDragThreshold)
-                // You can request a lower or higher threshold using the second parameter of IsMouseDragging() and GetMouseDragDelta()
-                ImVec2 value_raw = ImGui::GetMouseDragDelta(0, 0.0f);
-                ImVec2 value_with_lock_threshold = ImGui::GetMouseDragDelta(0);
-                ImVec2 mouse_delta = io.MouseDelta;
-                ImGui::SameLine(); ImGui::Text("Raw (%.1f, %.1f), WithLockThresold (%.1f, %.1f), MouseDelta (%.1f, %.1f)", value_raw.x, value_raw.y, value_with_lock_threshold.x, value_with_lock_threshold.y, mouse_delta.x, mouse_delta.y);
-            }
+                ImGui::GetForegroundDrawList()->AddLine(io.MouseClickedPos[0], io.MousePos, ImGui::GetColorU32(ImGuiCol_Button), 4.0f); // Draw a line between the button and the mouse cursor
+
+            // Drag operations gets "unlocked" when the mouse has moved past a certain threshold (the default threshold is stored in io.MouseDragThreshold)
+            // You can request a lower or higher threshold using the second parameter of IsMouseDragging() and GetMouseDragDelta()
+            ImVec2 value_raw = ImGui::GetMouseDragDelta(0, 0.0f);
+            ImVec2 value_with_lock_threshold = ImGui::GetMouseDragDelta(0);
+            ImVec2 mouse_delta = io.MouseDelta;
+            ImGui::Text("GetMouseDragDelta(0):\n  w/ default threshold: (%.1f, %.1f),\n  w/ zero threshold: (%.1f, %.1f)\nMouseDelta: (%.1f, %.1f)", value_with_lock_threshold.x, value_with_lock_threshold.y, value_raw.x, value_raw.y, mouse_delta.x, mouse_delta.y);
             ImGui::TreePop();
         }