From 17035c7480e12c816ed13e4dcd75b3fac9802798 Mon Sep 17 00:00:00 2001
From: Andrea Bogazzi <andreabogazzi79@gmail.com>
Date: Mon, 24 Apr 2017 02:13:18 +0200
Subject: [PATCH] reduce angle calculation error for cosin of 90 and 270
 degrees (#3872)

* reduce angle calculation error

* reduce angle calculation error
---
 src/canvas.class.js                 | 23 ++++++++++++-----------
 src/mixins/object_geometry.mixin.js |  4 ++++
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/canvas.class.js b/src/canvas.class.js
index a8179c4d5b7..5adaa13f51f 100644
--- a/src/canvas.class.js
+++ b/src/canvas.class.js
@@ -976,13 +976,6 @@
           angle = radiansToDegrees(curAngle - lastAngle + t.theta),
           hasRoated = true;
 
-      // normalize angle to positive value
-      if (angle < 0) {
-        angle = 360 + angle;
-      }
-
-      angle %= 360;
-
       if (t.target.snapAngle > 0) {
         var snapAngle  = t.target.snapAngle,
             snapThreshold  = t.target.snapThreshold || snapAngle,
@@ -995,13 +988,21 @@
         else if (Math.abs(angle - rightAngleLocked) < snapThreshold) {
           angle = rightAngleLocked;
         }
+      }
 
-        if (t.target.angle === angle) {
-          hasRoated = false;
-        }
+      // normalize angle to positive value
+      if (angle < 0) {
+        angle = 360 + angle;
+      }
+      angle %= 360;
+
+      if (t.target.angle === angle) {
+        hasRoated = false;
+      }
+      else {
+        t.target.angle = angle;
       }
 
-      t.target.angle = angle;
       return hasRoated;
     },
 
diff --git a/src/mixins/object_geometry.mixin.js b/src/mixins/object_geometry.mixin.js
index 152d8d7b5d8..52ebd87d2aa 100644
--- a/src/mixins/object_geometry.mixin.js
+++ b/src/mixins/object_geometry.mixin.js
@@ -450,6 +450,10 @@
     _calcRotateMatrix: function() {
       if (this.angle) {
         var theta = degreesToRadians(this.angle), cos = Math.cos(theta), sin = Math.sin(theta);
+        // trying to keep rounding error small, ugly but it works.
+        if (cos === 6.123233995736766e-17 || cos === -1.8369701987210297e-16) {
+          cos = 0;
+        }
         return [cos, sin, -sin, cos, 0, 0];
       }
       return fabric.iMatrix.concat();