Mat44Arg: add an isIdentity() method

Author: stephengold

src/main/java/com/github/stephengold/joltjni/Mat44.java

@@ -453,6 +453,20 @@ public boolean isEqual(Mat44Arg m2) {
         return result;
     }
 
+    /**
+     * Test whether the current matrix is an identity matrix. The matrix is
+     * unaffected.
+     *
+     * @return {@code true} if exactly equal, otherwise {@code false}
+     */
+    @Override
+    public boolean isIdentity() {
+        long matrixVa = va();
+        boolean result = isIdentity(matrixVa);
+
+        return result;
+    }
+
     /**
      * Multiply the current matrix by the argument. The current matrix is
      * unaffected.
@@ -635,6 +649,8 @@ native private static void getQuaternion(
 
     native private static long inversedRotationTranslation(long currentVa);
 
+    native private static boolean isIdentity(long matrixVa);
+
     native private static long multiply(long m1Va, long m2Va);
 
     native private static long multiply3x3(long currentVa, long argVa);

src/main/java/com/github/stephengold/joltjni/readonly/Mat44Arg.java

@@ -1,5 +1,5 @@
 /*
-Copyright (c) 2024 Stephen Gold
+Copyright (c) 2024-2025 Stephen Gold
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -101,6 +101,14 @@ public interface Mat44Arg extends ConstJoltPhysicsObject {
      */
     boolean isEqual(Mat44Arg m2);
 
+    /**
+     * Test whether the current matrix is an identity matrix. The matrix is
+     * unaffected.
+     *
+     * @return {@code true} if equal, {@code false} if unequal
+     */
+    boolean isIdentity();
+
     /**
      * Multiply the current matrix by the specified matrix. The current matrix
      * is unaffected.

src/main/native/glue/m/Mat44.cpp

@@ -293,6 +293,18 @@ JNIEXPORT jlong JNICALL Java_com_github_stephengold_joltjni_Mat44_inversedRotati
     return reinterpret_cast<jlong> (pResult);
 }
 
+/*
+ * Class:     com_github_stephengold_joltjni_Mat44
+ * Method:    isIdentity
+ * Signature: (J)Z
+ */
+JNIEXPORT jboolean JNICALL Java_com_github_stephengold_joltjni_Mat44_isIdentity
+  (JNIEnv *, jclass, jlong matrixVa) {
+    const Mat44 * const pMatrix = reinterpret_cast<Mat44 *> (matrixVa);
+    const bool result = (*pMatrix == Mat44::sIdentity());
+    return result;
+}
+
 /*
  * Class:     com_github_stephengold_joltjni_Mat44
  * Method:    multiply