IO: Input queue trickling adjustment for touch screens. (#2702, #4921)

+ amend two comments in imgui.h

docs/CHANGELOG.txt

@@ -58,6 +58,16 @@ Other changes:
   Windows Close and Collapse Buttons.
 - Misc: Fixed ImVec2 operator[] violating aliasing rules causing issue with Intel C++
   compiler. (#6272) [@BayesBug]
+- IO: Input queue trickling adjustment for touch screens. (#2702, #4921)
+  This fixes single-tapping to move simulated mouse and immediately click on a widget
+  that is using the ImGuiButtonFlags_AllowItemOverlap policy.
+  - This only works if the backend can distinguish TouchScreen vs Mouse.
+    See 'Demo->Tools->Metrics->Inputs->Mouse Source' to verify.
+  - Fixed tapping on BeginTabItem() on a touch-screen. (#2702)
+  - Fixed tapping on CollapsingHeader() with a close button on a touch-screen.
+  - Fixed tapping on TreeNode() using ImGuiTreeNodeFlags_AllowItemOverlap on a touch-screen.
+  - Fixed tapping on Selectable() using ImGuiSelectableFlags_AllowItemOverlap on a touch-screen.
+  - Fixed tapping on TableHeader() on a touch-screen.
 - IO: Added io.AddMouseSourceEvent() and ImGuiMouseSource enum. This is to allow backend to
   specify actual event source between Mouse/TouchScreen/Pen. (#2702, #2334, #2372, #3453, #5693)
 - IO: Fixed support for calling io.AddXXXX functions fron inactive context (wrongly

imgui.cpp

@@ -8733,6 +8733,8 @@ void ImGui::UpdateInputEvents(bool trickle_fast_inputs)
             IM_ASSERT(button >= 0 && button < ImGuiMouseButton_COUNT);
             if (trickle_fast_inputs && ((mouse_button_changed & (1 << button)) || mouse_wheeled))
                 break;
+            if (trickle_fast_inputs && e->MouseButton.MouseSource == ImGuiMouseSource_TouchScreen && mouse_moved) // #2702: TouchScreen have no initial hover.
+                break;
             io.MouseDown[button] = e->MouseButton.Down;
             io.MouseSource = e->MouseButton.MouseSource;
             mouse_button_changed |= (1 << button);

imgui.h

@@ -167,7 +167,7 @@ struct ImGuiViewport;               // A Platform Window (always only one in 'ma
 //   In Visual Studio IDE: CTRL+comma ("Edit.GoToAll") can follow symbols in comments, whereas CTRL+F12 ("Edit.GoToImplementation") cannot.
 //   With Visual Assist installed: ALT+G ("VAssistX.GoToImplementation") can also follow symbols in comments.
 enum ImGuiKey : int;                // -> enum ImGuiKey              // Enum: A key identifier (ImGuiKey_XXX or ImGuiMod_XXX value)
-enum ImGuiMouseSource : int;        // -> enum ImGuiMouseSource      // Enum; A mouse input source identifier (Mouse, TouchPad, TouchScreen, Pen)
+enum ImGuiMouseSource : int;        // -> enum ImGuiMouseSource      // Enum; A mouse input source identifier (Mouse, TouchScreen, Pen)
 typedef int ImGuiCol;               // -> enum ImGuiCol_             // Enum: A color identifier for styling
 typedef int ImGuiCond;              // -> enum ImGuiCond_            // Enum: A condition for many Set*() functions
 typedef int ImGuiDataType;          // -> enum ImGuiDataType_        // Enum: A primary data type
@@ -2049,7 +2049,7 @@ struct ImGuiIO
     bool        MouseDown[5];                       // Mouse buttons: 0=left, 1=right, 2=middle + extras (ImGuiMouseButton_COUNT == 5). Dear ImGui mostly uses left and right buttons. Other buttons allow 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. >0 scrolls Up, <0 scrolls Down. Hold SHIFT to turn vertical scroll into horizontal scroll.
     float       MouseWheelH;                        // Mouse wheel Horizontal. >0 scrolls Left, <0 scrolls Right. Most users don't have a mouse with a horizontal wheel, may not be filled by all backends.
-    ImGuiMouseSource MouseSource;                   // Mouse actual input peripheral (Mouse/TouchPad/TouchScreen/Pen).
+    ImGuiMouseSource MouseSource;                   // Mouse actual input peripheral (Mouse/TouchScreen/Pen).
     bool        KeyCtrl;                            // Keyboard modifier down: Control
     bool        KeyShift;                           // Keyboard modifier down: Shift
     bool        KeyAlt;                             // Keyboard modifier down: Alt