From f1b1ba8963ff152d995c3cd132bc0755413bc44f Mon Sep 17 00:00:00 2001
From: swittk <switt1995@gmail.com>
Date: Wed, 28 Jul 2021 18:34:45 -0700
Subject: [PATCH] Makes "force" property available to Apple Pencil based
 events. (#31780)

Summary:
Fixes https://github.com/facebook/react-native/issues/31779

For more detailed explanation, see issue https://github.com/facebook/react-native/issues/31779

React Native touch handler events (onTouchStart, onTouchMoved, etc..) are intended to have "force" properties when used on devices which support pressure input (3D Touch & Apple Pencil events). However, due to a check in RCTForceTouchAvailable() function which checks for UITraitCollection's "forceTouchCapability" to be equal to UIForceTouchCapabilityAvailable, the check returns NO on iPad-based devices, due to iPad devices returning UIForceTouchCapabilityUnavailable at all times. This causes "force" values of Apple Pencils to never be passed on to React Native.
Since simply passing 0 as a value for force across the RN bridge for every touch event seemed like a change that might seem jarring to some, I decided that a simple additional boolean check if the touch event's type is UITouchTypePencil (this is the same as UITouchTypeStylus) should also suffice.

## Changelog

<!-- Help reviewers and the release process by writing your own changelog entry. For an example, see:
https://github.com/facebook/react-native/wiki/Changelog
-->

[iOS] [Fixed] - Fixed "force" property of touch events for Apple Pencil/Stylus devices.
[iOS] [Feature] - Added "altitudeAngle" property to touch events from Apple Pencil/Stylus devices.

Pull Request resolved: https://github.com/facebook/react-native/pull/31780

Test Plan:
The code compiles and runs, and trying a simple handler for a View like
````
  touchMove = (e: GestureResponderEvent) => {
    console.log(`pressure, altitude (${e.nativeEvent.force}, ${e.nativeEvent.altitudeAngle})`);
````
results in
<img width="424" alt="Screen Shot 2564-06-28 at 17 13 22" src="https://user-images.githubusercontent.com/5000572/123621055-0b563f00-d835-11eb-9eff-526ba27fdf7b.png">
and when pencil is oriented perpendicular to the screen and pressed with full force shows
<img width="412" alt="Screen Shot 2564-06-28 at 17 13 58" src="https://user-images.githubusercontent.com/5000572/123621139-1c06b500-d835-11eb-8207-68a49720d708.png">

Reviewed By: sammy-SC

Differential Revision: D29964102

Pulled By: sota000

fbshipit-source-id: 5a1f41d64c6fe325afbd2b9579eaf20a522e92dc
---
 React/Base/RCTTouchHandler.m | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/React/Base/RCTTouchHandler.m b/React/Base/RCTTouchHandler.m
index bfcadc3d607335..d1754c93e158d2 100644
--- a/React/Base/RCTTouchHandler.m
+++ b/React/Base/RCTTouchHandler.m
@@ -175,6 +175,10 @@ - (void)_updateReactTouchAtIndex:(NSInteger)touchIndex
   if (RCTForceTouchAvailable()) {
     reactTouch[@"force"] = @(RCTZeroIfNaN(nativeTouch.force / nativeTouch.maximumPossibleForce));
   }
+  else if (nativeTouch.type == UITouchTypePencil) {
+    reactTouch[@"force"] = @(RCTZeroIfNaN(nativeTouch.force / nativeTouch.maximumPossibleForce));
+    reactTouch[@"altitudeAngle"] = @(RCTZeroIfNaN(nativeTouch.altitudeAngle));
+  }
 }
 
 /**