From 028769f54f66fcdabc369f59b94ac18c51801d99 Mon Sep 17 00:00:00 2001
From: NathanSweet <nathan.sweet@gmail.com>
Date: Fri, 30 Jan 2015 17:59:11 +0100
Subject: [PATCH] Fixed single bone IK with flipping and y-up coordinate
 systems.

---
 spine-as3/spine-as3/src/spine/IkConstraint.as | 4 +++-
 spine-c/src/spine/IkConstraint.c              | 4 +++-
 spine-csharp/src/IkConstraint.cs              | 4 +++-
 spine-js/spine.js                             | 4 +++-
 spine-lua/IkConstraint.lua                    | 6 +++++-
 5 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/spine-as3/spine-as3/src/spine/IkConstraint.as b/spine-as3/spine-as3/src/spine/IkConstraint.as
index 7e754b6d0..f51070e0c 100644
--- a/spine-as3/spine-as3/src/spine/IkConstraint.as
+++ b/spine-as3/spine-as3/src/spine/IkConstraint.as
@@ -77,7 +77,9 @@ public class IkConstraint {
 	static public function apply1 (bone:Bone, targetX:Number, targetY:Number, alpha:Number) : void {
 		var parentRotation:Number = (!bone._data.inheritRotation || bone._parent == null) ? 0 : bone._parent._worldRotation;
 		var rotation:Number = bone.rotation;
-		var rotationIK:Number = Math.atan2(targetY - bone._worldY, targetX - bone._worldX) * radDeg - parentRotation;
+		var rotationIK:Number = Math.atan2(targetY - bone._worldY, targetX - bone._worldX) * radDeg;
+		if (bone._worldFlipX != (bone._worldFlipY != Bone.yDown)) rotationIK = -rotationIK;
+		rotationIK -= parentRotation;
 		bone.rotationIK = rotation + (rotationIK - rotation) * alpha;
 	}
 
diff --git a/spine-c/src/spine/IkConstraint.c b/spine-c/src/spine/IkConstraint.c
index d23ada807..106b5ae51 100644
--- a/spine-c/src/spine/IkConstraint.c
+++ b/spine-c/src/spine/IkConstraint.c
@@ -69,7 +69,9 @@ void spIkConstraint_apply (spIkConstraint* self) {
 void spIkConstraint_apply1 (spBone* bone, float targetX, float targetY, float alpha) {
 	float parentRotation = (!bone->data->inheritRotation || !bone->parent) ? 0 : bone->parent->worldRotation;
 	float rotation = bone->rotation;
-	float rotationIK = ATAN2(targetY - bone->worldY, targetX - bone->worldX) * RAD_DEG - parentRotation;
+	float rotationIK = ATAN2(targetY - bone->worldY, targetX - bone->worldX) * RAD_DEG;
+	if (bone->worldFlipX != (bone->worldFlipY != yDown)) rotationIK = -rotationIK;
+	rotationIK -= parentRotation;
 	bone->rotationIK = rotation + (rotationIK - rotation) * alpha;
 }
 
diff --git a/spine-csharp/src/IkConstraint.cs b/spine-csharp/src/IkConstraint.cs
index 6261e083a..a2816e796 100644
--- a/spine-csharp/src/IkConstraint.cs
+++ b/spine-csharp/src/IkConstraint.cs
@@ -82,7 +82,9 @@ namespace Spine {
 		static public void apply (Bone bone, float targetX, float targetY, float alpha) {
 			float parentRotation = (!bone.data.inheritRotation || bone.parent == null) ? 0 : bone.parent.worldRotation;
 			float rotation = bone.rotation;
-			float rotationIK = (float)Math.Atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg - parentRotation;
+			float rotationIK = (float)Math.Atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg;
+			if (bone.worldFlipX != (bone.worldFlipY != Bone.yDown)) rotationIK = -rotationIK;
+			rotationIK -= parentRotation;
 			bone.rotationIK = rotation + (rotationIK - rotation) * alpha;
 		}
 
diff --git a/spine-js/spine.js b/spine-js/spine.js
index 522cc3f72..215b5c89e 100644
--- a/spine-js/spine.js
+++ b/spine-js/spine.js
@@ -226,7 +226,9 @@ spine.IkConstraint.prototype = {
 spine.IkConstraint.apply1 = function (bone, targetX, targetY, alpha) {
 	var parentRotation = (!bone.data.inheritRotation || !bone.parent) ? 0 : bone.parent.worldRotation;
 	var rotation = bone.rotation;
-	var rotationIK = Math.atan2(targetY - bone.worldY, targetX - bone.worldX) * spine.radDeg - parentRotation;
+	var rotationIK = Math.atan2(targetY - bone.worldY, targetX - bone.worldX) * spine.radDeg;
+	if (bone.worldFlipX != (bone.worldFlipY != spine.Bone.yDown)) rotationIK = -rotationIK;
+	rotationIK -= parentRotation;
 	bone.rotationIK = rotation + (rotationIK - rotation) * alpha;
 };
 /** Adjusts the parent and child bone rotations so the tip of the child is as close to the target position as possible. The
diff --git a/spine-lua/IkConstraint.lua b/spine-lua/IkConstraint.lua
index 7a23187b5..96317bdc8 100644
--- a/spine-lua/IkConstraint.lua
+++ b/spine-lua/IkConstraint.lua
@@ -72,7 +72,11 @@ function IkConstraint.apply1 (bone, targetX, targetY, alpha)
 		parentRotation = bone.parent.worldRotation
 	end
 	local rotation = bone.rotation
-	local rotationIK = math.atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg - parentRotation
+	local rotationIK = math.atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg
+	if bone.worldFlipX ~= bone.worldFlipY then
+		rotationIK = -rotationIK
+	end
+	rotationIK = rotationIK - parentRotation
 	bone.rotationIK = rotation + (rotationIK - rotation) * alpha
 end