vec2.lerp

bpl · May 3, 2012 · 5874379 · 5874379
1 parent dc9808e
commit 5874379
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diff --git a/gl-matrix.js b/gl-matrix.js
@@ -2502,6 +2502,23 @@
         return dest;
     };
 
+    /**
+     * Performs a linear interpolation between two vec2
+     *
+     * @param {vec2} vecA First vector
+     * @param {vec2} vecB Second vector
+     * @param {Number} lerp Interpolation amount between the two inputs
+     * @param {vec2} [dest] vec2 receiving operation result. If not specified result is written to vecA
+     *
+     * @returns {vec2} dest if specified, vecA otherwise
+     */
+    vec2.lerp = function (vecA, vecB, lerp, dest) {
+        if (!dest) { dest = vecA; }
+        dest[0] = vecA[0] + lerp * (vecB[0] - vecA[0]);
+        dest[1] = vecA[1] + lerp * (vecB[1] - vecA[1]);
+        return dest;
+    };
+
     /*
      * Exports
      */

diff --git a/spec/javascripts/vec2_spec.js b/spec/javascripts/vec2_spec.js
@@ -13,6 +13,23 @@ describe("vec2", function() {
     });
   });
 
+  describe("lerp", function() {
+    describe("with dest", function() {
+      beforeEach(function() { result = vec2.lerp(vecA, vecB, 0.5, dest); });
+      it("should return dest", function() { expect(result).toBe(dest); });
+      it("should set dest to correct value", function() { expect(dest).toBeEqualish([2, 3]); });
+      it("should not modify vecA", function() { expect(vecA).toBeEqualish([1, 2]); });
+      it("should not modify vecB", function() { expect(vecB).toBeEqualish([3, 4]); });
+    });
+
+    describe("without dest", function() {
+      beforeEach(function() { result = vec2.lerp(vecA, vecB); });
+      it("should return vecA", function() { expect(result).toBe(vecA); });
+      it("should modify vecA", function() { expect(vecA).toBeEqualish([2, 3]); });
+      it("should not modify vecB", function() { expect(vecB).toBeEqualish([3, 4]); });
+    });
+  });
+
   describe("direction", function() {
     describe("with dest", function() {
       beforeEach(function() { result = vec2.direction(vecA, vecB, dest); });