On second thought, the math optimizations are OK.

(reverted from commit 547ea760d82c3c7e1dc825704eb2046a218317b1)
If inaccuracy becomes a problem at runtime (which is unlikely), users can decide to remove the optimizations.

spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/Bone.java

@@ -94,8 +94,7 @@ public class Bone implements Updatable {
 		appliedScaleX = scaleX;
 		appliedScaleY = scaleY;
 
-		rotation *= MathUtils.degRad;
-		float cos = (float)Math.cos(rotation), sin = (float)Math.sin(rotation);
+		float cos = MathUtils.cosDeg(rotation), sin = MathUtils.sinDeg(rotation);
 		float la = cos * scaleX, lb = -sin * scaleY, lc = sin * scaleX, ld = cos * scaleY;
 		Bone parent = this.parent;
 		if (parent == null) { // Root bone.
@@ -139,9 +138,8 @@ public class Bone implements Updatable {
 				pc = 0;
 				pd = 1;
 				do {
-					rotation = parent.appliedRotation * MathUtils.degRad;
-					cos = (float)Math.cos(rotation);
-					sin = (float)Math.sin(rotation);
+					cos = MathUtils.cosDeg(parent.appliedRotation);
+					sin = MathUtils.sinDeg(parent.appliedRotation);
 					float temp = pa * cos + pb * sin;
 					pb = pa * -sin + pb * cos;
 					pa = temp;
@@ -162,9 +160,9 @@ public class Bone implements Updatable {
 				pc = 0;
 				pd = 1;
 				do {
-					rotation = parent.appliedRotation * MathUtils.degRad;
-					cos = (float)Math.cos(rotation);
-					sin = (float)Math.sin(rotation);
+					float r = parent.appliedRotation;
+					cos = MathUtils.cosDeg(r);
+					sin = MathUtils.sinDeg(r);
 					float psx = parent.appliedScaleX, psy = parent.appliedScaleY;
 					float za = cos * psx, zb = -sin * psy, zc = sin * psx, zd = cos * psy;
 					float temp = pa * za + pb * zc;
@@ -174,9 +172,9 @@ public class Bone implements Updatable {
 					pd = pc * zb + pd * zd;
 					pc = temp;
 
-					if (psx < 0) rotation = -rotation;
-					cos = (float)Math.cos(-rotation);
-					sin = (float)Math.sin(-rotation);
+					if (psx < 0) r = -r;
+					cos = MathUtils.cosDeg(-r);
+					sin = MathUtils.sinDeg(-r);
 					temp = pa * cos + pb * sin;
 					pb = pa * -sin + pb * cos;
 					pa = temp;
@@ -318,11 +316,11 @@ public class Bone implements Updatable {
 	}
 
 	public float getWorldRotationX () {
-		return (float)Math.atan2(c, a) * MathUtils.radDeg;
+		return MathUtils.atan2(c, a) * MathUtils.radDeg;
 	}
 
 	public float getWorldRotationY () {
-		return (float)Math.atan2(d, b) * MathUtils.radDeg;
+		return MathUtils.atan2(d, b) * MathUtils.radDeg;
 	}
 
 	public float getWorldScaleX () {

spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/IkConstraint.java

@@ -124,7 +124,7 @@ public class IkConstraint implements Updatable {
 	static public void apply (Bone bone, float targetX, float targetY, float alpha) {
 		float parentRotation = bone.parent == null ? 0 : bone.parent.getWorldRotationX();
 		float rotation = bone.rotation;
-		float rotationIK = (float)Math.atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg - parentRotation;
+		float rotationIK = atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg - parentRotation;
 		if ((bone.worldSignX != bone.worldSignY) != (bone.skeleton.flipX != bone.skeleton.flipY)) rotationIK = 360 - rotationIK;
 		if (rotationIK > 180)
 			rotationIK -= 360;
@@ -190,10 +190,10 @@ public class IkConstraint implements Updatable {
 				cos = -1;
 			else if (cos > 1) cos = 1;
 			a2 = (float)Math.acos(cos) * bendDir;
-			float a = l1 + l2 * cos, o = l2 * (float)Math.sin(a2);
-			a1 = (float)Math.atan2(ty * a - tx * o, tx * a + ty * o);
+			float a = l1 + l2 * cos, o = l2 * sin(a2);
+			a1 = atan2(ty * a - tx * o, tx * a + ty * o);
 		} else {
-			float a = psx * l2, b = psy * l2, ta = (float)Math.atan2(ty, tx);
+			float a = psx * l2, b = psy * l2, ta = atan2(ty, tx);
 			float aa = a * a, bb = b * b, ll = l1 * l1, dd = tx * tx + ty * ty;
 			float c0 = bb * ll + aa * dd - aa * bb, c1 = -2 * bb * l1, c2 = bb - aa;
 			float d = c1 * c1 - 4 * c2 * c0;
@@ -205,8 +205,8 @@ public class IkConstraint implements Updatable {
 				float r = Math.abs(r0) < Math.abs(r1) ? r0 : r1;
 				if (r * r <= dd) {
 					float y = (float)Math.sqrt(dd - r * r) * bendDir;
-					a1 = ta - (float)Math.atan2(y, r);
-					a2 = (float)Math.atan2(y / psy, (r - l1) / psx);
+					a1 = ta - atan2(y, r);
+					a2 = atan2(y / psy, (r - l1) / psx);
 					break outer;
 				}
 			}
@@ -226,8 +226,8 @@ public class IkConstraint implements Updatable {
 				minX = x;
 			}
 			float angle = (float)Math.acos(-a * l1 / (aa - bb));
-			x = a * (float)Math.cos(angle) + l1;
-			float y = b * (float)Math.sin(angle);
+			x = a * cos(angle) + l1;
+			float y = b * sin(angle);
 			dist = x * x + y * y;
 			if (dist < minDist) {
 				minAngle = angle;
@@ -242,14 +242,14 @@ public class IkConstraint implements Updatable {
 				maxY = y;
 			}
 			if (dd <= (minDist + maxDist) / 2) {
-				a1 = ta - (float)Math.atan2(minY * bendDir, minX);
+				a1 = ta - atan2(minY * bendDir, minX);
 				a2 = minAngle * bendDir;
 			} else {
-				a1 = ta - (float)Math.atan2(maxY * bendDir, maxX);
+				a1 = ta - atan2(maxY * bendDir, maxX);
 				a2 = maxAngle * bendDir;
 			}
 		}
-		float os = (float)Math.atan2(cy, cx) * s2;
+		float os = atan2(cy, cx) * s2;
 		a1 = (a1 - os) * radDeg + os1;
 		a2 = (a2 + os) * radDeg * s2 + os2;
 		if (a1 > 180)

spine-libgdx/spine-libgdx/src/com/esotericsoftware/spine/attachments/RegionAttachment.java

@@ -92,9 +92,9 @@ public class RegionAttachment extends Attachment {
 		localY *= scaleY;
 		localX2 *= scaleX;
 		localY2 *= scaleY;
-		float rotation = getRotation() * MathUtils.degRad;
-		float cos = (float)Math.cos(rotation);
-		float sin = (float)Math.sin(rotation);
+		float rotation = getRotation();
+		float cos = MathUtils.cosDeg(rotation);
+		float sin = MathUtils.sinDeg(rotation);
 		float x = getX();
 		float y = getY();
 		float localXCos = localX * cos + x;