Optimize creating an identity matrix (#365)

Since we're starting from zero, only update the needed elements

Author: kevmoo

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 2.4.0-wip
 
 - Remove the deprecated `SimplexNoise` class.
+- Optimized the `identity` constructors on the `Matrix` classes.
 
 ## 2.3.0
 

lib/src/vector_math/matrix2.dart

@@ -62,7 +62,10 @@ class Matrix2 {
   Matrix2.zero() : _m2storage = Float32List(4);
 
   /// Identity matrix.
-  factory Matrix2.identity() => Matrix2.zero()..setIdentity();
+  factory Matrix2.identity() =>
+      Matrix2.zero()
+        .._m2storage[0] = 1.0
+        .._m2storage[3] = 1.0;
 
   /// Copies values from [other].
   factory Matrix2.copy(Matrix2 other) => Matrix2.zero()..setFrom(other);

lib/src/vector_math/matrix3.dart

@@ -131,7 +131,11 @@ class Matrix3 {
   Matrix3.zero() : _m3storage = Float32List(9);
 
   /// Identity matrix.
-  factory Matrix3.identity() => Matrix3.zero()..setIdentity();
+  factory Matrix3.identity() =>
+      Matrix3.zero()
+        .._m3storage[0] = 1.0
+        .._m3storage[4] = 1.0
+        .._m3storage[8] = 1.0;
 
   /// Copes values from [other].
   factory Matrix3.copy(Matrix3 other) => Matrix3.zero()..setFrom(other);

lib/src/vector_math/matrix4.dart

@@ -245,7 +245,12 @@ class Matrix4 {
   Matrix4.zero() : _m4storage = Float32List(16);
 
   /// Identity matrix.
-  factory Matrix4.identity() => Matrix4.zero()..setIdentity();
+  factory Matrix4.identity() =>
+      Matrix4.zero()
+        .._m4storage[0] = 1.0
+        .._m4storage[5] = 1.0
+        .._m4storage[10] = 1.0
+        .._m4storage[15] = 1.0;
 
   /// Copies values from [other].
   factory Matrix4.copy(Matrix4 other) => Matrix4.zero()..setFrom(other);
@@ -1777,7 +1782,7 @@ class Matrix4 {
   /// Computes the result of `arg x this` and stores the result in-place in
   /// `this`.
   ///
-  /// This method does not alter the [Matrix4] in `arg`.
+  /// This method does not alter the [Matrix4] in [arg].
   void leftMultiply(Matrix4 arg) {
     final argStorage = arg._m4storage;
     final m00 = argStorage[0];

lib/src/vector_math_64/matrix2.dart

@@ -62,7 +62,10 @@ class Matrix2 {
   Matrix2.zero() : _m2storage = Float64List(4);
 
   /// Identity matrix.
-  factory Matrix2.identity() => Matrix2.zero()..setIdentity();
+  factory Matrix2.identity() =>
+      Matrix2.zero()
+        .._m2storage[0] = 1.0
+        .._m2storage[3] = 1.0;
 
   /// Copies values from [other].
   factory Matrix2.copy(Matrix2 other) => Matrix2.zero()..setFrom(other);

lib/src/vector_math_64/matrix3.dart

@@ -131,7 +131,11 @@ class Matrix3 {
   Matrix3.zero() : _m3storage = Float64List(9);
 
   /// Identity matrix.
-  factory Matrix3.identity() => Matrix3.zero()..setIdentity();
+  factory Matrix3.identity() =>
+      Matrix3.zero()
+        .._m3storage[0] = 1.0
+        .._m3storage[4] = 1.0
+        .._m3storage[8] = 1.0;
 
   /// Copes values from [other].
   factory Matrix3.copy(Matrix3 other) => Matrix3.zero()..setFrom(other);

lib/src/vector_math_64/matrix4.dart

@@ -245,7 +245,12 @@ class Matrix4 {
   Matrix4.zero() : _m4storage = Float64List(16);
 
   /// Identity matrix.
-  factory Matrix4.identity() => Matrix4.zero()..setIdentity();
+  factory Matrix4.identity() =>
+      Matrix4.zero()
+        .._m4storage[0] = 1.0
+        .._m4storage[5] = 1.0
+        .._m4storage[10] = 1.0
+        .._m4storage[15] = 1.0;
 
   /// Copies values from [other].
   factory Matrix4.copy(Matrix4 other) => Matrix4.zero()..setFrom(other);