From f7da9204c13ad098bba18e36864eca7a60cf4f35 Mon Sep 17 00:00:00 2001
From: Henrik Rydgard <hrydgard@gmail.com>
Date: Wed, 5 Apr 2017 09:57:26 +0200
Subject: [PATCH] Allow using any touchId to scroll. Should help #9554.

---
 ext/native/ui/viewgroup.cpp |  8 +++++---
 ext/native/ui/viewgroup.h   | 30 +++++++++++-------------------
 2 files changed, 16 insertions(+), 22 deletions(-)

diff --git a/ext/native/ui/viewgroup.cpp b/ext/native/ui/viewgroup.cpp
index bd7a25d8c59d..2c0e248599ff 100644
--- a/ext/native/ui/viewgroup.cpp
+++ b/ext/native/ui/viewgroup.cpp
@@ -734,25 +734,27 @@ const float friction = 0.92f;
 const float stop_threshold = 0.1f;
 
 void ScrollView::Touch(const TouchInput &input) {
-	if ((input.flags & TOUCH_DOWN) && input.id == 0) {
+	if ((input.flags & TOUCH_DOWN) && scrollTouchId_ == -1) {
 		scrollStart_ = scrollPos_;
 		inertia_ = 0.0f;
+		scrollTouchId_ = input.id;
 	}
 
 	Gesture gesture = orientation_ == ORIENT_VERTICAL ? GESTURE_DRAG_VERTICAL : GESTURE_DRAG_HORIZONTAL;
 
-	if (input.flags & TOUCH_UP) {
+	if ((input.flags & TOUCH_UP) && input.id == scrollTouchId_) {
 		float info[4];
 		if (gesture_.GetGestureInfo(gesture, info)) {
 			inertia_ = info[1];
 		}
+		scrollTouchId_ = -1;
 	}
 
 	TouchInput input2;
 	if (CanScroll()) {
 		input2 = gesture_.Update(input, bounds_);
 		float info[4];
-		if (gesture_.GetGestureInfo(gesture, info) && !(input.flags & TOUCH_DOWN)) {
+		if (gesture_.GetGestureInfo(gesture, info) && !(input.flags & TOUCH_DOWN) && input.id == scrollTouchId_) {
 			float pos = scrollStart_ - info[0];
 			scrollPos_ = pos;
 			scrollTarget_ = pos;
diff --git a/ext/native/ui/viewgroup.h b/ext/native/ui/viewgroup.h
index 8dcf49b57563..65d89a5a1ff4 100644
--- a/ext/native/ui/viewgroup.h
+++ b/ext/native/ui/viewgroup.h
@@ -222,17 +222,8 @@ class GridLayout : public ViewGroup {
 // A scrollview usually contains just a single child - a linear layout or similar.
 class ScrollView : public ViewGroup {
 public:
-	ScrollView(Orientation orientation, LayoutParams *layoutParams = 0) :
-		ViewGroup(layoutParams),
-		orientation_(orientation),
-		scrollPos_(0),
-		scrollStart_(0),
-		scrollTarget_(0),
-		scrollToTarget_(false),
-		inertia_(0.0f),
-		pull_(0.0f),
-		lastViewSize_(0.0f),
-		scrollToTopOnSizeChange_(false) {}
+	ScrollView(Orientation orientation, LayoutParams *layoutParams = 0)
+		: ViewGroup(layoutParams), orientation_(orientation) {}
 
 	void Measure(const UIContext &dc, MeasureSpec horiz, MeasureSpec vert) override;
 	void Layout() override;
@@ -261,14 +252,15 @@ class ScrollView : public ViewGroup {
 
 	GestureDetector gesture_;
 	Orientation orientation_;
-	float scrollPos_;
-	float scrollStart_;
-	float scrollTarget_;
-	bool scrollToTarget_;
-	float inertia_;
-	float pull_;
-	float lastViewSize_;
-	bool scrollToTopOnSizeChange_;
+	float scrollPos_ = 0.0f;
+	float scrollStart_ = 0.0f;
+	float scrollTarget_ = 0.0f;
+	int scrollTouchId_ = -1;
+	bool scrollToTarget_ = false;
+	float inertia_ = 0.0f;
+	float pull_ = 0.0f;
+	float lastViewSize_ = 0.0f;
+	bool scrollToTopOnSizeChange_ = false;
 };
 
 class ViewPager : public ScrollView {