Fix math.smoothstep and smootherstep when min is greater than max

src/core/math/math.js

@@ -253,18 +253,18 @@ const math = {
      *
      * See https://en.wikipedia.org/wiki/Smoothstep for more details.
      *
-     * @param {number} min - The lower bound of the interpolation range.
-     * @param {number} max - The upper bound of the interpolation range.
+     * @param {number} min - The value of x at which the result is 0. Can be greater than max for a
+     * falling ramp.
+     * @param {number} max - The value of x at which the result is 1.
      * @param {number} x - The value to interpolate.
      * @returns {number} The smoothly interpolated value clamped between zero and one.
      * @example
      * math.smoothstep(0, 10, 5); // returns 0.5
      */
     smoothstep(min, max, x) {
-        if (x <= min) return 0;
-        if (x >= max) return 1;
+        if (min === max) return x <= min ? 0 : 1;
 
-        x = (x - min) / (max - min);
+        x = math.clamp((x - min) / (max - min), 0, 1);
 
         return x * x * (3 - 2 * x);
     },
@@ -275,18 +275,18 @@ const math = {
      *
      * See https://en.wikipedia.org/wiki/Smoothstep#Variations for more details.
      *
-     * @param {number} min - The lower bound of the interpolation range.
-     * @param {number} max - The upper bound of the interpolation range.
+     * @param {number} min - The value of x at which the result is 0. Can be greater than max for a
+     * falling ramp.
+     * @param {number} max - The value of x at which the result is 1.
      * @param {number} x - The value to interpolate.
      * @returns {number} The smoothly interpolated value clamped between zero and one.
      * @example
      * math.smootherstep(0, 10, 5); // returns 0.5
      */
     smootherstep(min, max, x) {
-        if (x <= min) return 0;
-        if (x >= max) return 1;
+        if (min === max) return x <= min ? 0 : 1;
 
-        x = (x - min) / (max - min);
+        x = math.clamp((x - min) / (max - min), 0, 1);
 
         return x * x * x * (x * (x * 6 - 15) + 10);
     },

test/core/math/math.test.mjs

@@ -324,6 +324,25 @@ describe('math', function () {
             expect(math.smootherstep(0, 10, 10)).to.equal(1);
         });
 
+        it('clamps x outside the range', function () {
+            expect(math.smootherstep(0, 10, -5)).to.equal(0);
+            expect(math.smootherstep(0, 10, 15)).to.equal(1);
+        });
+
+        it('returns a falling ramp when min is greater than max', function () {
+            expect(math.smootherstep(10, 0, 15)).to.equal(0);
+            expect(math.smootherstep(10, 0, 5)).to.equal(0.5);
+            expect(math.smootherstep(10, 0, -5)).to.equal(1);
+            expect(math.smootherstep(-0.3, -0.6, -0.2)).to.equal(0);
+            expect(math.smootherstep(-0.3, -0.6, -0.7)).to.equal(1);
+        });
+
+        it('returns a step when min equals max', function () {
+            expect(math.smootherstep(5, 5, 4)).to.equal(0);
+            expect(math.smootherstep(5, 5, 5)).to.equal(0);
+            expect(math.smootherstep(5, 5, 6)).to.equal(1);
+        });
+
     });
 
     describe('#smoothstep', function () {
@@ -340,6 +359,25 @@ describe('math', function () {
             expect(math.smoothstep(0, 10, 10)).to.equal(1);
         });
 
+        it('clamps x outside the range', function () {
+            expect(math.smoothstep(0, 10, -5)).to.equal(0);
+            expect(math.smoothstep(0, 10, 15)).to.equal(1);
+        });
+
+        it('returns a falling ramp when min is greater than max', function () {
+            expect(math.smoothstep(10, 0, 15)).to.equal(0);
+            expect(math.smoothstep(10, 0, 5)).to.equal(0.5);
+            expect(math.smoothstep(10, 0, -5)).to.equal(1);
+            expect(math.smoothstep(-0.3, -0.6, -0.2)).to.equal(0);
+            expect(math.smoothstep(-0.3, -0.6, -0.7)).to.equal(1);
+        });
+
+        it('returns a step when min equals max', function () {
+            expect(math.smoothstep(5, 5, 4)).to.equal(0);
+            expect(math.smoothstep(5, 5, 5)).to.equal(0);
+            expect(math.smoothstep(5, 5, 6)).to.equal(1);
+        });
+
     });
 
 });