Inputs, IO: record MouseWheelRequestAxisSwap information. Apply in UpdateMouseWheel() before legacy ctrl+wheel.

imgui.cpp

@@ -8436,6 +8436,13 @@ static void ImGui::UpdateMouseInputs()
     ImGuiContext& g = *GImGui;
     ImGuiIO& io = g.IO;
 
+    // Mouse Wheel swapping flag
+    // As a standard behavior holding SHIFT while using Vertical Mouse Wheel triggers Horizontal scroll instead
+    // - We avoid doing it on OSX as it the OS input layer handles this already.
+    // - FIXME: However this means when running on OSX over Emscripten, Shift+WheelY will incur two swapping (1 in OS, 1 here), canceling the feature.
+    // - FIXME: When we can distinguish e.g. touchpad scroll events from mouse ones, we'll set this accordingly based on input source.
+    io.MouseWheelRequestAxisSwap = io.KeyShift && !io.ConfigMacOSXBehaviors;
+
     // Round mouse position to avoid spreading non-rounded position (e.g. UpdateManualResize doesn't support them well)
     if (IsMousePosValid(&io.MousePos))
         io.MousePos = g.MouseLastValidPos = ImFloorSigned(io.MousePos);
@@ -8596,15 +8603,9 @@ void ImGui::UpdateMouseWheel()
         return;
 
     // Mouse wheel scrolling
-    // As a standard behavior holding SHIFT while using Vertical Mouse Wheel triggers Horizontal scroll instead
-    // - We avoid doing it on OSX as it the OS input layer handles this already.
-    // - However this means when running on OSX over Emcripten, Shift+WheelY will incur two swappings (1 in OS, 1 here), cancelling the feature.
-    const bool swap_axis = g.IO.KeyShift && !g.IO.ConfigMacOSXBehaviors;
-    if (swap_axis)
-    {
-        wheel.x = wheel.y;
-        wheel.y = 0.0f;
-    }
+    // Read about io.MouseWheelRequestAxisSwap and its issue on Mac+Emscripten in UpdateMouseInputs()
+    if (g.IO.MouseWheelRequestAxisSwap)
+        wheel = ImVec2(wheel.y, 0.0f);
 
     // Maintain a rough average of moving magnitude on both axises
     // FIXME: should by based on wall clock time rather than frame-counter

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               "1.89.5 WIP"
-#define IMGUI_VERSION_NUM           18945
+#define IMGUI_VERSION_NUM           18946
 #define IMGUI_HAS_TABLE
 
 /*
@@ -2054,6 +2054,7 @@ struct ImGuiIO
     bool        MouseReleased[5];                   // Mouse button went from Down to !Down
     bool        MouseDownOwned[5];                  // Track if button was clicked inside a dear imgui window or over void blocked by a popup. We don't request mouse capture from the application if click started outside ImGui bounds.
     bool        MouseDownOwnedUnlessPopupClose[5];  // Track if button was clicked inside a dear imgui window.
+    bool        MouseWheelRequestAxisSwap;          // On a non-Mac system, holding SHIFT requests WheelY to perform the equivalent of a WheelX event. On a Mac system this is already enforced by the system.
     float       MouseDownDuration[5];               // Duration the mouse button has been down (0.0f == just clicked)
     float       MouseDownDurationPrev[5];           // Previous time the mouse button has been down
     float       MouseDragMaxDistanceSqr[5];         // Squared maximum distance of how much mouse has traveled from the clicking point (used for moving thresholds)