Added support for mousewheel on iOS

src/video/uikit/SDL_uikitview.m

@@ -66,6 +66,13 @@ extern int SDL_AppleTVRemoteOpenedAsJoystick;
         UISwipeGestureRecognizer *swipeRight = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(swipeGesture:)];
         swipeRight.direction = UISwipeGestureRecognizerDirectionRight;
         [self addGestureRecognizer:swipeRight];
+#else
+        if (@available(iOS 13.4, *)) {
+            UIPanGestureRecognizer *mouseWheelRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(mouseWheelGesture:)];
+            mouseWheelRecognizer.allowedScrollTypesMask = UIScrollTypeMaskDiscrete;
+            mouseWheelRecognizer.allowedTouchTypes = @[ @(UITouchTypeIndirectPointer) ];
+            [self addGestureRecognizer:mouseWheelRecognizer];
+        }
 #endif
 
         self.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
@@ -428,6 +435,29 @@ extern int SDL_AppleTVRemoteOpenedAsJoystick;
 
 #endif /* TARGET_OS_TV || defined(__IPHONE_9_1) */
 
+-(void)mouseWheelGesture:(UIPanGestureRecognizer *)gesture
+{
+    if (gesture.state == UIGestureRecognizerStateBegan ||
+        gesture.state == UIGestureRecognizerStateChanged ||
+        gesture.state == UIGestureRecognizerStateEnded) {
+        CGPoint velocity = [gesture velocityInView:self];
+
+        if (velocity.x > 0.0f) {
+            velocity.x = -1.0;
+        } else if (velocity.x < 0.0f) {
+            velocity.x = 1.0f;
+        }
+        if (velocity.y > 0.0f) {
+            velocity.y = -1.0;
+        } else if (velocity.y < 0.0f) {
+            velocity.y = 1.0f;
+        }
+        if (velocity.x != 0.0f || velocity.y != 0.0f) {
+            SDL_SendMouseWheel(sdlwindow, 0, velocity.x, velocity.y, SDL_MOUSEWHEEL_NORMAL);
+        }
+    }
+}
+
 #if TARGET_OS_TV
 -(void)swipeGesture:(UISwipeGestureRecognizer *)gesture
 {