mat2.multiplyVec2

bpl · May 3, 2012 · 9d8005a · 9d8005a
1 parent f783ba2
commit 9d8005a
Showing 2 changed files with 37 additions and 0 deletions.
diff --git a/gl-matrix.js b/gl-matrix.js
@@ -2682,6 +2682,23 @@
         return dest;
     }
 
+    /**
+     * Multiplies the vec2 by the given 2x2 matrix
+     *
+     * @param {mat2} matrix the 2x2 matrix to multiply against
+     * @param {vec2} vec    the vector to multiply
+     * @param {vec2} [dest] an optional receiving vector. If not given, vec is used.
+     *
+     * @returns {vec2} The multiplication result
+     **/
+    mat2.multiplyVec2 = function(matrix, vec, dest) {
+      if (!dest) dest = vec;
+      var x = vec[0], y = vec[1];
+      dest[0] = x * matrix[0] + y * matrix[1];
+      dest[1] = x * matrix[2] + y * matrix[3];
+      return dest;
+    };
+
     /*
      * Exports
      */

diff --git a/spec/javascripts/mat2_spec.js b/spec/javascripts/mat2_spec.js
@@ -102,4 +102,24 @@ describe("mat2", function() {
       it("should return a", function() { expect(result).toBe(a); });
     });
   });
+
+  describe("multiplyVec2", function() {
+    beforeEach(function() { b = [5, 6]; dest = [0, 0]; });
+
+    describe("with dest", function() {
+      beforeEach(function() { result = mat2.multiplyVec2(a, b, dest); });
+      it("should set dest", function() { expect(dest).toBeEqualish([17, 39]); });
+      it("should return dest", function() { expect(result).toBe(dest); });
+      it("should not modify a", function() { expect(a).toBeEqualish([1, 2, 3, 4]); });
+      it("should not modify b", function() { expect(b).toBeEqualish([5, 6]); });
+    });
+
+    describe("without dest", function() {
+      beforeEach(function() { result = mat2.multiplyVec2(a, b); });
+      it("should not change a", function() { expect(a).toBeEqualish([1, 2, 3, 4]); });
+      it("should change b", function() { expect(b).toBeEqualish([17, 39]); });
+      it("should return b", function() { expect(result).toBe(b); });
+    });
+  });
+
 });