[core] Fix gestures for `PLATFORM_DESKTOP_SDL` (#3499)

* Fix gestures for SDL

* Review the gesture handling for SDL

* Review 2

src/platforms/rcore_desktop_sdl.c

@@ -964,6 +964,15 @@ void PollInputEvents(void)
     // so, if mouse is not moved it returns a (0, 0) position... this behaviour should be reviewed!
     //for (int i = 0; i < MAX_TOUCH_POINTS; i++) CORE.Input.Touch.position[i] = (Vector2){ 0, 0 };
 
+    // Map touch position to mouse position for convenience
+    // WARNING: If the target desktop device supports touch screen, this behavious should be reviewed!
+    // https://www.codeproject.com/Articles/668404/Programming-for-Multi-Touch
+    // https://docs.microsoft.com/en-us/windows/win32/wintouch/getting-started-with-multi-touch-messages
+    CORE.Input.Touch.position[0] = CORE.Input.Mouse.currentPosition;
+
+    int touchAction = -1;       // 0-TOUCH_ACTION_UP, 1-TOUCH_ACTION_DOWN, 2-TOUCH_ACTION_MOVE
+    bool gestureUpdate = false; // Flag to note gestures require to update
+
     // Register previous keys states
     // NOTE: Android supports up to 260 keys
     for (int i = 0; i < MAX_KEYBOARD_KEYS; i++)
@@ -1077,10 +1086,16 @@ void PollInputEvents(void)
             case SDL_MOUSEBUTTONDOWN:
             {
                 CORE.Input.Mouse.currentButtonState[event.button.button - 1] = 1;
+
+                touchAction = 1;
+                gestureUpdate = true;
             } break;
             case SDL_MOUSEBUTTONUP:
             {
                 CORE.Input.Mouse.currentButtonState[event.button.button - 1] = 0;
+
+                touchAction = 0;
+                gestureUpdate = true;
             } break;
             case SDL_MOUSEWHEEL:
             {
@@ -1100,6 +1115,10 @@ void PollInputEvents(void)
                     CORE.Input.Mouse.currentPosition.x = (float)event.motion.x;
                     CORE.Input.Mouse.currentPosition.y = (float)event.motion.y;
                 }
+
+                CORE.Input.Touch.position[0] = CORE.Input.Mouse.currentPosition;
+                touchAction = 2;
+                gestureUpdate = true;
             } break;
 
             // Check gamepad events
@@ -1122,11 +1141,38 @@ void PollInputEvents(void)
             } break;
             default: break;
         }
+
+#if defined(SUPPORT_GESTURES_SYSTEM)
+        if (gestureUpdate)
+        {
+            // Process mouse events as touches to be able to use mouse-gestures
+            GestureEvent gestureEvent = { 0 };
+
+            // Register touch actions
+            gestureEvent.touchAction = touchAction;
+
+            // Assign a pointer ID
+            gestureEvent.pointId[0] = 0;
+
+            // Register touch points count
+            gestureEvent.pointCount = 1;
+
+            // Register touch points position, only one point registered
+            if (touchAction == 2) gestureEvent.position[0] = CORE.Input.Touch.position[0];
+            else gestureEvent.position[0] = GetMousePosition();
+
+            // Normalize gestureEvent.position[0] for CORE.Window.screen.width and CORE.Window.screen.height
+            gestureEvent.position[0].x /= (float)GetScreenWidth();
+            gestureEvent.position[0].y /= (float)GetScreenHeight();
+
+            // Gesture data is sent to gestures-system for processing
+            ProcessGestureEvent(gestureEvent);
+        }
+#endif
     }
     //-----------------------------------------------------------------------------
 }
 
-
 //----------------------------------------------------------------------------------
 // Module Internal Functions Definition
 //----------------------------------------------------------------------------------