Inputs, Scrolling: better selection of scrolling window when hovering nested windows and backend/OS is emitting dual-axis wheeling inputs. (#3795, #4559)

docs/CHANGELOG.txt

@@ -39,6 +39,10 @@ Breaking changes:
 
 Other changes:
 
+- Inputs, Scrolling: better selection of scrolling window when hovering nested windows
+  and when backend/OS is emitting dual-axis wheeling inputs (typically touch pads on macOS).
+  We now select a primary axis based on recent events, and select a target window based on it.
+  We expect this behavior to be further improved/tweaked. (#3795, #4559) [@ocornut, @folays]
 - Text: fixed layouting of wrapped-text block when the last source line is above the
   clipping region. Regression added in 1.89. (#5720, #5919)
 - Misc: fixed parameters to IMGUI_DEBUG_LOG() not being dead-stripped when building

imgui.cpp

@@ -4367,13 +4367,58 @@ static void LockWheelingWindow(ImGuiWindow* window, float wheel_amount)
     IMGUI_DEBUG_LOG_IO("LockWheelingWindow() \"%s\"\n", window ? window->Name : "NULL");
     g.WheelingWindow = window;
     g.WheelingWindowRefMousePos = g.IO.MousePos;
+    if (window == NULL)
+    {
+        g.WheelingWindowStartFrame = -1;
+        g.WheelingAxisAvg = ImVec2(0.0f, 0.0f);
+    }
+}
+
+static ImGuiWindow* FindBestWheelingWindow(const ImVec2& wheel)
+{
+    // For each axis, find window in the hierarchy that may want to use scrolling
+    ImGuiContext& g = *GImGui;
+    ImGuiWindow* windows[2] = { NULL, NULL };
+    for (int axis = 0; axis < 2; axis++)
+        if (wheel[axis] != 0.0f)
+            for (ImGuiWindow* window = windows[axis] = g.HoveredWindow; window->Flags & ImGuiWindowFlags_ChildWindow; window = windows[axis] = window->ParentWindow)
+            {
+                // Bubble up into parent window if:
+                // - a child window doesn't allow any scrolling.
+                // - a child window has the ImGuiWindowFlags_NoScrollWithMouse flag.
+                //// - a child window doesn't need scrolling because it is already at the edge for the direction we are going in (FIXME-WIP)
+                const bool has_scrolling = (window->ScrollMax[axis] != 0.0f);
+                const bool inputs_disabled = (window->Flags & ImGuiWindowFlags_NoScrollWithMouse) && !(window->Flags & ImGuiWindowFlags_NoMouseInputs);
+                //const bool scrolling_past_limits = (wheel_v < 0.0f) ? (window->Scroll[axis] <= 0.0f) : (window->Scroll[axis] >= window->ScrollMax[axis]);
+                if (has_scrolling && !inputs_disabled) // && !scrolling_past_limits)
+                    break; // select this window
+            }
+    if (windows[0] == NULL && windows[1] == NULL)
+        return NULL;
+
+    // If there's only one window or only one axis then there's no ambiguity
+    if (windows[0] == windows[1] || windows[0] == NULL || windows[1] == NULL)
+        return windows[1] ? windows[1] : windows[0];
+
+    // If candidate are different windows we need to decide which one to prioritize
+    // - First frame: only find a winner if one axis is zero.
+    // - Subsequent frames: only find a winner when one is more than the other.
+    if (g.WheelingWindowStartFrame == -1)
+        g.WheelingWindowStartFrame = g.FrameCount;
+    if ((g.WheelingWindowStartFrame == g.FrameCount && wheel.x != 0.0f && wheel.y != 0.0f) || (g.WheelingAxisAvg.x == g.WheelingAxisAvg.y))
+    {
+        g.WheelingWindowWheelRemainder = wheel;
+        return NULL;
+    }
+    return (g.WheelingAxisAvg.x > g.WheelingAxisAvg.y) ? windows[0] : windows[1];
 }
 
 void ImGui::UpdateMouseWheel()
 {
     ImGuiContext& g = *GImGui;
 
-    // Reset the locked window if we move the mouse or after the timer elapses
+    // Reset the locked window if we move the mouse or after the timer elapses.
+    // FIXME: Ideally we could refactor to have one timer for "changing window w/ same axis" and a shorter timer for "changing window or axis w/ other axis" (#3795)
     if (g.WheelingWindow != NULL)
     {
         g.WheelingWindowReleaseTimer -= g.IO.DeltaTime;
@@ -4386,8 +4431,6 @@ void ImGui::UpdateMouseWheel()
     ImVec2 wheel;
     wheel.x = TestKeyOwner(ImGuiKey_MouseWheelX, ImGuiKeyOwner_None) ? g.IO.MouseWheelH : 0.0f;
     wheel.y = TestKeyOwner(ImGuiKey_MouseWheelY, ImGuiKeyOwner_None) ? g.IO.MouseWheel : 0.0f;
-    if (wheel.x == 0.0f && wheel.y == 0.0f)
-        return;
 
     //IMGUI_DEBUG_LOG("MouseWheel X:%.3f Y:%.3f\n", wheel_x, wheel_y);
     ImGuiWindow* mouse_window = g.WheelingWindow ? g.WheelingWindow : g.HoveredWindow;
@@ -4425,39 +4468,41 @@ void ImGui::UpdateMouseWheel()
         wheel.y = 0.0f;
     }
 
-    // Vertical Mouse Wheel scrolling
+    // Maintain a rough average of moving magnitude on both axises
-    // Bubble up into parent window if:
+    // FIXME: should by based on wall clock time rather than frame-counter
-    // - a child window doesn't allow any scrolling.
+    g.WheelingAxisAvg.x = ImExponentialMovingAverage(g.WheelingAxisAvg.x, ImAbs(wheel.x), 30);
-    // - a child window doesn't need scrolling because it is already at the edge for the direction we are going in.
+    g.WheelingAxisAvg.y = ImExponentialMovingAverage(g.WheelingAxisAvg.y, ImAbs(wheel.y), 30);
-    // - a child window has the ImGuiWindowFlags_NoScrollWithMouse flag.
-    if (wheel.y != 0.0f)
-    {
-        ImGuiWindow* window = mouse_window;
-        while ((window->Flags & ImGuiWindowFlags_ChildWindow) && ((window->ScrollMax.y == 0.0f) || ((window->Flags & ImGuiWindowFlags_NoScrollWithMouse) && !(window->Flags & ImGuiWindowFlags_NoMouseInputs))))
-            window = window->ParentWindow;
-        if (!(window->Flags & ImGuiWindowFlags_NoScrollWithMouse) && !(window->Flags & ImGuiWindowFlags_NoMouseInputs))
-        {
-            LockWheelingWindow(mouse_window, wheel.y);
-            float max_step = window->InnerRect.GetHeight() * 0.67f;
-            float scroll_step = ImFloor(ImMin(5 * window->CalcFontSize(), max_step));
-            SetScrollY(window, window->Scroll.y - wheel.y * scroll_step);
-        }
-    }
 
-    // Horizontal Mouse Wheel scrolling, or Vertical Mouse Wheel w/ Shift held
+    // In the rare situation where FindBestWheelingWindow() had to defer first frame of wheeling due to ambiguous main axis, reinject it now.
-    if (wheel.x != 0.0f)
+    wheel += g.WheelingWindowWheelRemainder;
-    {
+    g.WheelingWindowWheelRemainder = ImVec2(0.0f, 0.0f);
-        ImGuiWindow* window = mouse_window;
+    if (wheel.x == 0.0f && wheel.y == 0.0f)
-        while ((window->Flags & ImGuiWindowFlags_ChildWindow) && ((window->ScrollMax.x == 0.0f) || ((window->Flags & ImGuiWindowFlags_NoScrollWithMouse) && !(window->Flags & ImGuiWindowFlags_NoMouseInputs))))
+        return;
-            window = window->ParentWindow;
+
+    // Mouse wheel scrolling: find target and apply
+    // - don't renew lock if axis doesn't apply on the window.
+    // - select a main axis when both axises are being moved.
+    if (ImGuiWindow* window = (g.WheelingWindow ? g.WheelingWindow : FindBestWheelingWindow(wheel)))
         if (!(window->Flags & ImGuiWindowFlags_NoScrollWithMouse) && !(window->Flags & ImGuiWindowFlags_NoMouseInputs))
         {
-            LockWheelingWindow(mouse_window, wheel.x);
+            bool do_scroll[2] = { wheel.x != 0.0f && window->ScrollMax.x != 0.0f, wheel.y != 0.0f && window->ScrollMax.y != 0.0f };
-            float max_step = window->InnerRect.GetWidth() * 0.67f;
+            if (do_scroll[ImGuiAxis_X] && do_scroll[ImGuiAxis_Y])
-            float scroll_step = ImFloor(ImMin(2 * window->CalcFontSize(), max_step));
+                do_scroll[(g.WheelingAxisAvg.x > g.WheelingAxisAvg.y) ? ImGuiAxis_Y : ImGuiAxis_X] = false;
-            SetScrollX(window, window->Scroll.x - wheel.x * scroll_step);
+            if (do_scroll[ImGuiAxis_X])
+            {
+                LockWheelingWindow(window, wheel.x);
+                float max_step = window->InnerRect.GetWidth() * 0.67f;
+                float scroll_step = ImFloor(ImMin(2 * window->CalcFontSize(), max_step));
+                SetScrollX(window, window->Scroll.x - wheel.x * scroll_step);
+            }
+            if (do_scroll[ImGuiAxis_Y])
+            {
+                LockWheelingWindow(window, wheel.y);
+                float max_step = window->InnerRect.GetHeight() * 0.67f;
+                float scroll_step = ImFloor(ImMin(5 * window->CalcFontSize(), max_step));
+                SetScrollY(window, window->Scroll.y - wheel.y * scroll_step);
+            }
         }
-    }
 }
 
 // The reason this is exposed in imgui_internal.h is: on touch-based system that don't have hovering, we want to dispatch inputs to the right target (imgui vs imgui+app)
@@ -8427,7 +8472,7 @@ static void DebugPrintInputEvent(const char* prefix, const ImGuiInputEvent* e)
     ImGuiContext& g = *GImGui;
     if (e->Type == ImGuiInputEventType_MousePos)    { if (e->MousePos.PosX == -FLT_MAX && e->MousePos.PosY == -FLT_MAX) IMGUI_DEBUG_LOG_IO("%s: MousePos (-FLT_MAX, -FLT_MAX)\n", prefix); else IMGUI_DEBUG_LOG_IO("%s: MousePos (%.1f, %.1f)\n", prefix, e->MousePos.PosX, e->MousePos.PosY); return; }
     if (e->Type == ImGuiInputEventType_MouseButton) { IMGUI_DEBUG_LOG_IO("%s: MouseButton %d %s\n", prefix, e->MouseButton.Button, e->MouseButton.Down ? "Down" : "Up"); return; }
-    if (e->Type == ImGuiInputEventType_MouseWheel)  { IMGUI_DEBUG_LOG_IO("%s: MouseWheel (%.1f, %.1f)\n", prefix, e->MouseWheel.WheelX, e->MouseWheel.WheelY); return; }
+    if (e->Type == ImGuiInputEventType_MouseWheel)  { IMGUI_DEBUG_LOG_IO("%s: MouseWheel (%.3f, %.3f)\n", prefix, e->MouseWheel.WheelX, e->MouseWheel.WheelY); return; }
     if (e->Type == ImGuiInputEventType_Key)         { IMGUI_DEBUG_LOG_IO("%s: Key \"%s\" %s\n", prefix, ImGui::GetKeyName(e->Key.Key), e->Key.Down ? "Down" : "Up"); return; }
     if (e->Type == ImGuiInputEventType_Text)        { IMGUI_DEBUG_LOG_IO("%s: Text: %c (U+%08X)\n", prefix, e->Text.Char, e->Text.Char); return; }
     if (e->Type == ImGuiInputEventType_Focus)       { IMGUI_DEBUG_LOG_IO("%s: AppFocused %d\n", prefix, e->AppFocused.Focused); return; }
@@ -13409,6 +13454,13 @@ void ImGui::ShowMetricsWindow(bool* p_open)
         Text("NavWindowingTarget: '%s'", g.NavWindowingTarget ? g.NavWindowingTarget->Name : "NULL");
         Unindent();
 
+        Text("MOUSE WHEELING");
+        Indent();
+        Text("WheelingWindow: '%s'", g.WheelingWindow ? g.WheelingWindow->Name : "NULL");
+        Text("WheelingWindowReleaseTimer: %.2f", g.WheelingWindowReleaseTimer);
+        Text("WheelingAxisAvg[] = { %.3f, %.3f }, Main Axis: %s", g.WheelingAxisAvg.x, g.WheelingAxisAvg.y, (g.WheelingAxisAvg.x > g.WheelingAxisAvg.y) ? "X" : (g.WheelingAxisAvg.x < g.WheelingAxisAvg.y) ? "Y" : "<none>");
+        Unindent();
+
         TreePop();
     }
 

imgui.h

@@ -23,7 +23,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM > 12345')
 #define IMGUI_VERSION               "1.89.2 WIP"
-#define IMGUI_VERSION_NUM           18912
+#define IMGUI_VERSION_NUM           18913
 #define IMGUI_HAS_TABLE
 
 /*

imgui_internal.h

@@ -477,6 +477,7 @@ static inline ImVec2 ImRotate(const ImVec2& v, float cos_a, float sin_a)
 static inline float  ImLinearSweep(float current, float target, float speed)    { if (current < target) return ImMin(current + speed, target); if (current > target) return ImMax(current - speed, target); return current; }
 static inline ImVec2 ImMul(const ImVec2& lhs, const ImVec2& rhs)                { return ImVec2(lhs.x * rhs.x, lhs.y * rhs.y); }
 static inline bool   ImIsFloatAboveGuaranteedIntegerPrecision(float f)          { return f <= -16777216 || f >= 16777216; }
+static inline float  ImExponentialMovingAverage(float avg, float sample, int n) { avg -= avg / n; avg += sample / n; return avg; }
 IM_MSVC_RUNTIME_CHECKS_RESTORE
 
 // Helpers: Geometry
@@ -1764,7 +1765,10 @@ struct ImGuiContext
     ImGuiWindow*            MovingWindow;                       // Track the window we clicked on (in order to preserve focus). The actual window that is moved is generally MovingWindow->RootWindow.
     ImGuiWindow*            WheelingWindow;                     // Track the window we started mouse-wheeling on. Until a timer elapse or mouse has moved, generally keep scrolling the same window even if during the course of scrolling the mouse ends up hovering a child window.
     ImVec2                  WheelingWindowRefMousePos;
+    int                     WheelingWindowStartFrame;           // This may be set one frame before WheelingWindow is != NULL
     float                   WheelingWindowReleaseTimer;
+    ImVec2                  WheelingWindowWheelRemainder;
+    ImVec2                  WheelingAxisAvg;
 
     // Item/widgets state and tracking information
     ImGuiID                 DebugHookIdInfo;                    // Will call core hooks: DebugHookIdInfo() from GetID functions, used by Stack Tool [next HoveredId/ActiveId to not pull in an extra cache-line]
@@ -2030,6 +2034,7 @@ struct ImGuiContext
         HoveredWindowUnderMovingWindow = NULL;
         MovingWindow = NULL;
         WheelingWindow = NULL;
+        WheelingWindowStartFrame = -1;
         WheelingWindowReleaseTimer = 0.0f;
 
         DebugHookIdInfo = 0;