Index: src/OF4x4Matrix.h
==================================================================
--- src/OF4x4Matrix.h
+++ src/OF4x4Matrix.h
@@ -19,11 +19,11 @@
 
 /**
  * @brief A 4x4 matrix of floats.
  */
 OF_SUBCLASSING_RESTRICTED
-@interface OF4x4Matrix: OFObject
+@interface OF4x4Matrix: OFObject <OFCopying>
 {
 	float _values[16];
 }
 
 #ifdef OF_HAVE_CLASS_PROPERTIES
@@ -60,8 +60,16 @@
 
 /**
  * @brief Transposes the matrix.
  */
 - (void)transpose;
+
+/**
+ * @brief Mulitplies the receiver with the specified matrix on the left side
+ *	  and the receiver on the right side.
+ *
+ * @param matrix The matrix to multiply the receiver with
+ */
+- (void)multiplyWithMatrix: (OF4x4Matrix *)matrix;
 @end
 
 OF_ASSUME_NONNULL_END

Index: src/OF4x4Matrix.m
==================================================================
--- src/OF4x4Matrix.m
+++ src/OF4x4Matrix.m
@@ -56,10 +56,15 @@
 
 - (float *)values
 {
 	return _values;
 }
+
+- (instancetype)copy
+{
+	return [[OF4x4Matrix alloc] initWithValues: _values];
+}
 
 - (bool)isEqual: (OF4x4Matrix *)matrix
 {
 	if (![matrix isKindOfClass: [OF4x4Matrix class]])
 		return false;
@@ -97,10 +102,81 @@
 	_values[11] = copy[14];
 	_values[12] = copy[3];
 	_values[13] = copy[7];
 	_values[14] = copy[11];
 }
+
+- (void)multiplyWithMatrix: (OF4x4Matrix *)matrix
+{
+	float copy[16];
+	memcpy(copy, _values, 16 * sizeof(float));
+
+	_values[0] = matrix->_values[0] * copy[0] +
+	    matrix->_values[4] * copy[1] +
+	    matrix->_values[8] * copy[2] +
+	    matrix->_values[12] * copy[3];
+	_values[1] = matrix->_values[1] * copy[0] +
+	    matrix->_values[5] * copy[1] +
+	    matrix->_values[9] * copy[2] +
+	    matrix->_values[13] * copy[3];
+	_values[2] = matrix->_values[2] * copy[0] +
+	    matrix->_values[6] * copy[1] +
+	    matrix->_values[10] * copy[2] +
+	    matrix->_values[14] * copy[3];
+	_values[3] = matrix->_values[3] * copy[0] +
+	    matrix->_values[7] * copy[1] +
+	    matrix->_values[11] * copy[2] +
+	    matrix->_values[15] * copy[3];
+	_values[4] = matrix->_values[0] * copy[4] +
+	    matrix->_values[4] * copy[5] +
+	    matrix->_values[8] * copy[6] +
+	    matrix->_values[12] * copy[7];
+	_values[5] = matrix->_values[1] * copy[4] +
+	    matrix->_values[5] * copy[5] +
+	    matrix->_values[9] * copy[6] +
+	    matrix->_values[13] * copy[7];
+	_values[6] = matrix->_values[2] * copy[4] +
+	    matrix->_values[6] * copy[5] +
+	    matrix->_values[10] * copy[6] +
+	    matrix->_values[14] * copy[7];
+	_values[7] = matrix->_values[3] * copy[4] +
+	    matrix->_values[7] * copy[5] +
+	    matrix->_values[11] * copy[6] +
+	    matrix->_values[15] * copy[7];
+	_values[8] = matrix->_values[0] * copy[8] +
+	    matrix->_values[4] * copy[9] +
+	    matrix->_values[8] * copy[10] +
+	    matrix->_values[12] * copy[11];
+	_values[9] = matrix->_values[1] * copy[8] +
+	    matrix->_values[5] * copy[9] +
+	    matrix->_values[9] * copy[10] +
+	    matrix->_values[13] * copy[11];
+	_values[10] = matrix->_values[2] * copy[8] +
+	    matrix->_values[6] * copy[9] +
+	    matrix->_values[10] * copy[10] +
+	    matrix->_values[14] * copy[11];
+	_values[11] = matrix->_values[3] * copy[8] +
+	    matrix->_values[7] * copy[9] +
+	    matrix->_values[11] * copy[10] +
+	    matrix->_values[15] * copy[11];
+	_values[12] = matrix->_values[0] * copy[12] +
+	    matrix->_values[4] * copy[13] +
+	    matrix->_values[8] * copy[14] +
+	    matrix->_values[12] * copy[15];
+	_values[13] = matrix->_values[1] * copy[12] +
+	    matrix->_values[5] * copy[13] +
+	    matrix->_values[9] * copy[14] +
+	    matrix->_values[13] * copy[15];
+	_values[14] = matrix->_values[2] * copy[12] +
+	    matrix->_values[6] * copy[13] +
+	    matrix->_values[10] * copy[14] +
+	    matrix->_values[14] * copy[15];
+	_values[15] = matrix->_values[3] * copy[12] +
+	    matrix->_values[7] * copy[13] +
+	    matrix->_values[11] * copy[14] +
+	    matrix->_values[15] * copy[15];
+}
 
 - (OFString *)description
 {
 	return [OFString stringWithFormat:
 	    @"<OF4x4Matrix: {\n"

Index: tests/OF4x4MatrixTests.m
==================================================================
--- tests/OF4x4MatrixTests.m
+++ tests/OF4x4MatrixTests.m
@@ -21,11 +21,11 @@
 
 @implementation TestsAppDelegate (OF4x4MatrixTests)
 - (void)_4x4MatrixTests
 {
 	void *pool = objc_autoreleasePoolPush();
-	OF4x4Matrix *matrix;
+	OF4x4Matrix *matrix, *matrix2;
 
 	TEST(@"+[identity]",
 	    memcmp([[OF4x4Matrix identity] values], (float [16]){
 		1, 0, 0, 0,
 		0, 1, 0, 0,
@@ -62,9 +62,30 @@
 		1, 0, 0, 0,
 		0, 1, 0, 0,
 		0, 0, 1, 0,
 		0, 0, 0, 1
 	    }]])
+
+	TEST(@"-[copy]", (matrix2 = [matrix copy]) && [matrix2 isEqual: matrix])
+
+	TEST(@"-[multiplyWithMatrix:] #1",
+	    R([matrix2 multiplyWithMatrix: [OF4x4Matrix identity]]) &&
+	    [matrix2 isEqual: matrix])
+
+	matrix2 = [OF4x4Matrix matrixWithValues: (float [16]){
+		100, 500,  900, 1300,
+		200, 600, 1000, 1400,
+		300, 700, 1100, 1500,
+		400, 800, 1200, 1600
+	}];
+	TEST(@"-[multiplyWithMatrix:] #2",
+	    R([matrix2 multiplyWithMatrix: matrix]) &&
+	    [matrix2 isEqual: [OF4x4Matrix matrixWithValues: (float [16]){
+		 9000, 20200, 31400, 42600,
+		10000, 22800, 35600, 48400,
+		11000, 25400, 39800, 54200,
+		12000, 28000, 44000, 60000
+	    }]])
 
 	objc_autoreleasePoolPop(pool);
 }
 @end