From 596c4945e32d43fe7b8a19ed994152aaf3d2e504 Mon Sep 17 00:00:00 2001
From: brentfpage <brentfpage@gmail.com>
Date: Tue, 29 Sep 2026 22:26:15 -0700
Subject: [PATCH] add support for SDL pinch events

---
 backends/imgui_impl_sdl3.cpp |  7 +++++++
 imgui.cpp                    | 25 +++++++++++++++++++++++++
 imgui.h                      |  3 +++
 3 files changed, 35 insertions(+)

diff --git a/backends/imgui_impl_sdl3.cpp b/backends/imgui_impl_sdl3.cpp
index 05f6498f1..07f75259c 100644
--- a/backends/imgui_impl_sdl3.cpp
+++ b/backends/imgui_impl_sdl3.cpp
@@ -477,6 +477,13 @@ bool ImGui_ImplSDL3_ProcessEvent(const SDL_Event* event)
             bd->WantUpdateGamepadsList = true;
             return true;
         }
+        case SDL_EVENT_PINCH_UPDATE:
+        {
+            io.AddMouseSourceEvent(ImGuiMouseSource_TouchScreen);
+            io.AddPinchUpdateEvent(event->pinch.scale, event->pinch.span_x, event->pinch.span_y, event->pinch.focus_x, event->pinch.focus_y);
+            return true;
+        }
+
         default:
             break;
     }
diff --git a/imgui.cpp b/imgui.cpp
index 57ed579af..1b9910849 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -2073,6 +2073,31 @@ void ImGuiIO::AddFocusEvent(bool focused)
     g.InputEventsQueue.push_back(e);
 }
 
+// Queue a pinch status update.  Represent the pinch event as a wheel event, using MouseWheel.Wheel(X|Y) for the pinch x|y amounts.  Pass the pinch centroid into PosOther.
+void ImGuiIO::AddPinchUpdateEvent(float scale, float span_x, float span_y, float focus_x, float focus_y)
+{
+    IM_ASSERT(Ctx != NULL);
+    ImGuiContext& g = *Ctx;
+
+    if (!AppAcceptingEvents || (scale == 1.0f))
+        return;
+    ImGuiInputEvent e;
+    e.Type = ImGuiInputEventType_MouseWheel;
+    e.Source = ImGuiInputSource_Mouse;
+    e.EventId = g.InputEventsNextEventId++;
+    float norm = ImSqrt(ImPow(span_x,2) + ImPow(span_y,2));
+    e.MouseWheel.WheelX = (1-scale)*100*span_x/norm;
+    e.MouseWheel.WheelY = (1-scale)*100*span_y/norm;
+    e.MouseWheel.MouseSource = g.InputEventsNextMouseSource;
+    g.InputEventsQueue.push_back(e);
+
+    ImVec2 finger_pos_middle(focus_x, focus_y);
+    g.IO.PosOther = finger_pos_middle;
+}
+
+
+
+
 ImGuiPlatformIO::ImGuiPlatformIO()
 {
     // Most fields are initialized with zero
diff --git a/imgui.h b/imgui.h
index a108888a2..aafd0ac13 100644
--- a/imgui.h
+++ b/imgui.h
@@ -2584,6 +2584,8 @@ struct ImGuiIO
     IMGUI_API void  AddMouseWheelEvent(float wheel_x, float wheel_y);       // Queue a mouse wheel update. wheel_y<0: scroll down, wheel_y>0: scroll up, wheel_x<0: scroll right, wheel_x>0: scroll left.
     IMGUI_API void  AddMouseSourceEvent(ImGuiMouseSource source);           // Queue a mouse source change (Mouse/TouchScreen/Pen)
     IMGUI_API void  AddFocusEvent(bool focused);                            // Queue a gain/loss of focus for the application (generally based on OS/platform focus of your window)
+    IMGUI_API void  AddPinchUpdateEvent(float scale, float span_x, float span_y, float focus_x, float focus_y);                            // Queue a pinch status update
+
     IMGUI_API void  AddInputCharacter(unsigned int c);                      // Queue a new character input
     IMGUI_API void  AddInputCharacterUTF16(ImWchar16 c);                    // Queue a new character input from a UTF-16 character, it can be a surrogate
     IMGUI_API void  AddInputCharactersUTF8(const char* str);                // Queue a new characters input from a UTF-8 string
@@ -2658,6 +2660,7 @@ struct ImGuiIO
     bool        AppAcceptingEvents;                 // Only modify via SetAppAcceptingEvents()
     ImWchar16   InputQueueSurrogate;                // For AddInputCharacterUTF16()
     ImVector<ImWchar> InputQueueCharacters;         // Queue of _characters_ input (obtained by platform backend). Fill using AddInputCharacter() helper.
+    ImVec2      PosOther;                           // Convenience slot for a screen position, e.g., the centroid of the two finger positions relevant to a pinch gesture on mobile
 
     // Legacy: before 1.87, we required backend to fill io.KeyMap[] (imgui->native map) during initialization and io.KeysDown[] (native indices) every frame.
     // This is still temporarily supported as a legacy feature. However the new preferred scheme is for backend to call io.AddKeyEvent().