From 1af47603cfbb12cec88df44654073be6f38276b2 Mon Sep 17 00:00:00 2001
From: Michael Ortiz <mike@glooko.com>
Date: Wed, 27 Apr 2016 22:07:30 -0700
Subject: [PATCH] Fix ReactNativeART arc drawing on Android

Summary:
**Motivation**: Arc drawing has been broken on Android for some time. dgladkov submitted a PR, which ended up having a bug and was never merged. This PR should fix that bug as well as provide screenshots to prove it works.

**Reproducing the Bug:** dgladkov made a simple test app which helps to illustrate the bug. The repo can be found [here](https://github.com/dgladkov/RNArtArcDrawingBug). The demo app illustrates that on iOS, wedges are drawn correctly, but Android only draws full circles. [Direct Link to iOS Before](https://github.com/dgladkov/RNArtArcDrawingBug/blob/master/images/ios.png). [Direct Link to Android Before](https://github.com/dgladkov/RNArtArcDrawingBug/blob/master/images/android.png).

**Proof The Bug is Fixed:** [Here is a direct link to Android After pic.](http://i.imgur.com/9dTU2Xn.png) You can see the wedges match the iOS Before screenshot.

**What went wrong:** dgladkov's solution relied on Java's modulus, which in fact, implements modulus in a non-standard way. Modulus should a
Closes https://github.com/facebook/react-native/pull/7049

Differential Revision: D3234404

Pulled By: spicyj

fb-gh-sync-id: 4974b818dc49d9d16f2483c49b462c459a8bb479
fbshipit-source-id: 4974b818dc49d9d16f2483c49b462c459a8bb479
---
 .../react/views/art/ARTShapeShadowNode.java   | 29 ++++++++++++++++---
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/art/ARTShapeShadowNode.java b/ReactAndroid/src/main/java/com/facebook/react/views/art/ARTShapeShadowNode.java
index ce8b5e136..21d8849ad 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/art/ARTShapeShadowNode.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/art/ARTShapeShadowNode.java
@@ -191,6 +191,20 @@ public class ARTShapeShadowNode extends ARTVirtualNode {
     return false;
   }
 
+  /**
+   * Returns the floor modulus of the float arguments. Java modulus will return a negative remainder
+   * when the divisor is negative. Modulus should always be positive. This mimics the behavior of
+   * Math.floorMod, introduced in Java 8.
+   */
+  private float modulus(float x, float y) {
+    float remainder = x % y;
+    float modulus = remainder;
+    if (remainder < 0) {
+      modulus += y;
+    }
+    return modulus;
+  }
+
   /**
    * Creates a {@link Path} from an array of instructions constructed by JS
    * (see ARTSerializablePath.js). Each instruction starts with a type (see PATH_TYPE_*) followed
@@ -232,11 +246,18 @@ public class ARTShapeShadowNode extends ARTVirtualNode {
           float r = data[i++] * mScale;
           float start = (float) Math.toDegrees(data[i++]);
           float end = (float) Math.toDegrees(data[i++]);
-          boolean clockwise = data[i++] == 0f;
-          if (!clockwise) {
-            end = 360 - end;
+          boolean clockwise = data[i++] == 1f;
+          float sweep = end - start;
+          if (Math.abs(sweep) > 360) {
+            sweep = 360;
+          } else {
+            sweep = modulus(sweep, 360);
           }
-          float sweep = start - end;
+          if (!clockwise && sweep < 360) {
+            start = end;
+            sweep = 360 - sweep;
+          }
+
           RectF oval = new RectF(x - r, y - r, x + r, y + r);
           path.addArc(oval, start, sweep);
           break;