feat(Color): add withAlpha method to create color copies with specified alpha

- Introduced a new method `withAlpha` in the Color class to return a copy of the color with a specified alpha value.
- Updated the Color class in both `littlejs.release.js` and `engineMath.js`.
- Added unit tests to verify the functionality of the new method, ensuring it returns a new instance with the correct alpha while leaving the original color unchanged.

Author: KilledByAPixel

REFERENCE.md

@@ -102,6 +102,7 @@ Color.HSLA()                              // Get the color in HSLA format
 Color.mutate(amount=.05, alphaAmount=0)   // Randomly diverge from this color
 Color.setHex(hex)                         // Set this color from a hex code
 Color.setAlpha(a=1)                       // Set the alpha of this color
+Color.withAlpha(a=1)                      // Get a copy of this color with the alpha set
 Color.rgbaInt()                           // Get this color as 32 bit RGBA value
 Color.toString(useAlpha=true)             // Get hex color code as a string
 

dist/littlejs.d.ts

@@ -1395,6 +1395,10 @@ declare module "littlejsengine" {
         /** Returns a new color that is a copy of this
          * @return {Color} */
         copy(): Color;
+        /** Returns a copy of this color with the alpha set
+         *  @param {number} [a] - alpha
+         *  @return {Color} */
+        withAlpha(a?: number): Color;
         /** Returns a copy of this color plus the color passed in
          * @param {Color} c - other color
          * @return {Color} */

dist/littlejs.esm.js

@@ -2247,6 +2247,11 @@ class Color
      * @return {Color} */
     copy() { return new Color(this.r, this.g, this.b, this.a); }
 
+    /** Returns a copy of this color with the alpha set
+     *  @param {number} [a] - alpha
+     *  @return {Color} */
+    withAlpha(a=1) { return new Color(this.r, this.g, this.b, a); }
+
     /** Returns a copy of this color plus the color passed in
      * @param {Color} c - other color
      * @return {Color} */

dist/littlejs.esm.min.js

@@ -2247,6 +2247,11 @@ class Color
      * @return {Color} */
     copy() { return new Color(this.r, this.g, this.b, this.a); }
 
+    /** Returns a copy of this color with the alpha set
+     *  @param {number} [a] - alpha
+     *  @return {Color} */
+    withAlpha(a=1) { return new Color(this.r, this.g, this.b, a); }
+
     /** Returns a copy of this color plus the color passed in
      * @param {Color} c - other color
      * @return {Color} */

dist/littlejs.js

@@ -1559,6 +1559,11 @@ class Color
      * @return {Color} */
     copy() { return new Color(this.r, this.g, this.b, this.a); }
 
+    /** Returns a copy of this color with the alpha set
+     *  @param {number} [a] - alpha
+     *  @return {Color} */
+    withAlpha(a=1) { return new Color(this.r, this.g, this.b, a); }
+
     /** Returns a copy of this color plus the color passed in
      * @param {Color} c - other color
      * @return {Color} */

dist/littlejs.min.js

@@ -938,6 +938,11 @@ class Color
      * @return {Color} */
     copy() { return new Color(this.r, this.g, this.b, this.a); }
 
+    /** Returns a copy of this color with the alpha set
+     *  @param {number} [a] - alpha
+     *  @return {Color} */
+    withAlpha(a=1) { return new Color(this.r, this.g, this.b, a); }
+
     /** Returns a copy of this color plus the color passed in
      * @param {Color} c - other color
      * @return {Color} */

dist/littlejs.release.js

@@ -647,6 +647,17 @@ test('Color setAlpha mutates alpha and returns self', () =>
     assert.equal(c.a, 1);
 });
 
+test('Color withAlpha returns a copy with new alpha', () =>
+{
+    const c = new Color(0.25, 0.5, 0.75, 1);
+    const r = c.withAlpha(0.5);
+    assert.equal(r.a, 0.5);                         // copy has the given alpha
+    assert.equal(r.r, 0.25); assert.equal(r.g, 0.5); assert.equal(r.b, 0.75); // rgb copied
+    assert.equal(c.a, 1);                           // original untouched
+    assert.notStrictEqual(r, c);                    // returns a new color, not self
+    assert.equal(new Color(1, 1, 1, 0.3).withAlpha().a, 1); // defaults to 1
+});
+
 test('Color divide', () =>
 {
     const r = new Color(1, 0.5, 0.25, 1).divide(new Color(2, 1, 0.5, 1));