From 4c10f9321c9d01dbcac4808e7e6674cba12f3aa5 Mon Sep 17 00:00:00 2001
From: Ranjan Shrestha <ranjan@sharingapples.com>
Date: Wed, 30 Jan 2019 09:45:10 -0800
Subject: [PATCH] Make perspective transformation look exactly same on iOS and
 Android (#18302)

Summary:
There is a variation in iOS and Android output while performing perspective transformation. The variation exists even when used in Android devices with different screen density.
Pull Request resolved: https://github.com/facebook/react-native/pull/18302

Differential Revision: D13877483

Pulled By: cpojer

fbshipit-source-id: e48be047a8047c7562722923a67666cb098243d8
---
 .../com/facebook/react/uimanager/BaseViewManager.java  | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/uimanager/BaseViewManager.java b/ReactAndroid/src/main/java/com/facebook/react/uimanager/BaseViewManager.java
index 0eeac09cf2a485..5e805675d4c243 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/uimanager/BaseViewManager.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/uimanager/BaseViewManager.java
@@ -44,7 +44,7 @@ public abstract class BaseViewManager<T extends View, C extends LayoutShadowNode
   private static final String PROP_TRANSLATE_Y = "translateY";
 
   private static final int PERSPECTIVE_ARRAY_INVERTED_CAMERA_DISTANCE_INDEX = 2;
-  private static final float CAMERA_DISTANCE_NORMALIZATION_MULTIPLIER = 5;
+  private static final float CAMERA_DISTANCE_NORMALIZATION_MULTIPLIER = (float)Math.sqrt(5);
 
   /**
    * Used to locate views in end-to-end (UI) tests.
@@ -234,8 +234,12 @@ private static void setTransformProperty(View view, ReadableArray transforms) {
       float scale = DisplayMetricsHolder.getScreenDisplayMetrics().density;
 
       // The following converts the matrix's perspective to a camera distance
-      // such that the camera perspective looks the same on Android and iOS
-      float normalizedCameraDistance = scale * cameraDistance * CAMERA_DISTANCE_NORMALIZATION_MULTIPLIER;
+      // such that the camera perspective looks the same on Android and iOS.
+      // The native Android implementation removed the screen density from the
+      // calculation, so squaring and a normalization value of
+      // sqrt(5) produces an exact replica with iOS.
+      // For more information, see https://github.com/facebook/react-native/pull/18302
+      float normalizedCameraDistance = scale * scale * cameraDistance * CAMERA_DISTANCE_NORMALIZATION_MULTIPLIER;
       view.setCameraDistance(normalizedCameraDistance);
 
     }