Fix imprecise rotations bug.

The bug this fixes is documented here: http://youtrack.sk89q.com/issue/WORLDEDIT-3220

worldedit-core/src/main/java/com/sk89q/worldedit/math/MathUtils.java

@@ -47,4 +47,62 @@ public final class MathUtils {
         return (int) (a - n * Math.floor(Math.floor(a) / n));
     }
 
+    /**
+     * Returns the cosine of an angle given in degrees. This is better than
+     * just {@code Math.cos(Math.toRadians(degrees))} because it provides a
+     * more accurate result for angles divisible by 90 degrees.
+     *
+     * @param degrees the angle
+     * @return the cosine of the given angle
+     */
+    public static double dCos(double degrees) {
+        int dInt = (int) degrees;
+        if (degrees == dInt && dInt % 90 == 0) {
+            dInt %= 360;
+            if (dInt < 0) {
+                dInt += 360;
+            }
+            switch (dInt) {
+            case 0:
+                return 1.0;
+            case 90:
+                return 0.0;
+            case 180:
+                return -1.0;
+            case 270:
+                return 0.0;
+            }
+        }
+        return Math.cos(Math.toRadians(degrees));
+    }
+
+    /**
+     * Returns the sine of an angle given in degrees. This is better than just
+     * {@code Math.cos(Math.toRadians(degrees))} because it provides a more
+     * accurate result for angles divisible by 90 degrees.
+     *
+     * @param degrees the angle
+     * @return the sine of the given angle
+     */
+    public static double dSin(double degrees) {
+        int dInt = (int) degrees;
+        if (degrees == dInt && dInt % 90 == 0) {
+            dInt %= 360;
+            if (dInt < 0) {
+                dInt += 360;
+            }
+            switch (dInt) {
+            case 0:
+                return 0.0;
+            case 90:
+                return 1.0;
+            case 180:
+                return 0.0;
+            case 270:
+                return -1.0;
+            }
+        }
+        return Math.cos(Math.toRadians(degrees));
+    }
+
 }

worldedit-core/src/main/java/com/sk89q/worldedit/math/transform/AffineTransform.java

@@ -20,6 +20,7 @@
 package com.sk89q.worldedit.math.transform;
 
 import com.sk89q.worldedit.Vector;
+import com.sk89q.worldedit.math.MathUtils;
 
 /**
  * An affine transform.
@@ -244,9 +245,8 @@ public class AffineTransform implements Transform {
     }
 
     public AffineTransform rotateX(double theta) {
-        theta = Math.toRadians(theta);
-        double cot = Math.cos(theta);
-        double sit = Math.sin(theta);
+        double cot = MathUtils.dCos(theta);
+        double sit = MathUtils.dSin(theta);
         return concatenate(
                 new AffineTransform(
                         1, 0, 0, 0,
@@ -255,9 +255,8 @@ public class AffineTransform implements Transform {
     }
 
     public AffineTransform rotateY(double theta) {
-        theta = Math.toRadians(theta);
-        double cot = Math.cos(theta);
-        double sit = Math.sin(theta);
+        double cot = MathUtils.dCos(theta);
+        double sit = MathUtils.dSin(theta);
         return concatenate(
                 new AffineTransform(
                         cot, 0, sit, 0,
@@ -266,9 +265,8 @@ public class AffineTransform implements Transform {
     }
 
     public AffineTransform rotateZ(double theta) {
-        theta = Math.toRadians(theta);
-        double cot = Math.cos(theta);
-        double sit = Math.sin(theta);
+        double cot = MathUtils.dCos(theta);
+        double sit = MathUtils.dSin(theta);
         return concatenate(
                 new AffineTransform(
                         cot, -sit, 0, 0,