Successfully implemented rotation and fixed drawing lines.

src/AudioClient.java

@@ -8,15 +8,17 @@ public class AudioClient {
     AudioPlayer.FORMAT = new XtFormat(new XtMix(sampleRate, XtSample.FLOAT32), 0, 0, 2, 0);
 
     // Draws a square.
-    Line l1 = new Line(-0.5f, -0.5f, 0.5f, -0.5f);
-    Line l2 = new Line(0.5f, -0.5f, 0.5f, 0.5f);
-    Line l3 = new Line(0.5f, 0.5f, -0.5f, 0.5f);
-    Line l4 = new Line(-0.5f, 0.5f, -0.5f, -0.5f);
+    Line l1 = new Line(-0.5, -0.5, 0.5, -0.5);
+    Line l2 = new Line(0.5, -0.5, 0.5, 0.5);
+    Line l3 = new Line(0.5, 0.5, -0.5, 0.5);
+    Line l4 = new Line(-0.5, 0.5, -0.5, -0.5);
 
     AudioPlayer.addLine(l1);
     AudioPlayer.addLine(l2);
     AudioPlayer.addLine(l3);
     AudioPlayer.addLine(l4);
+    
+    AudioPlayer.setRotateSpeed(0.4);
 
     player.start();
     while (true) {

src/AudioPlayer.java

@@ -9,6 +9,7 @@ public class AudioPlayer extends Thread {
   private static List<Line> lines = new ArrayList<>();
   private static int currentLine = 0;
   private static float FREQUENCY = 440;
+  private static double ROTATE_SPEED = 0;
   private static int framesDrawn = 0;
   private static double phase = 0;
 
@@ -17,15 +18,21 @@ public class AudioPlayer extends Thread {
     XtFormat format = stream.getFormat();
 
     for (int f = 0; f < frames; f++) {
-      Line line = currentLine();
-      line.rotate(nextTheta(stream.getFormat().mix.rate, 0.000001));
+      Line line;
+
+      if (ROTATE_SPEED == 0) {
+        line = currentLine();
+      } else {
+        line = currentLine().rotate(nextTheta(stream.getFormat().mix.rate, ROTATE_SPEED));
+      }
 
       int framesToDraw = (int) (line.length() * 100);
-      int neg = line.getX1() < line.getX2() || line.getY1() < line.getY2() ? 1 : -1;
+      int negX = line.getX1() < line.getX2()? 1 : -1;
+      int negY = line.getY1() < line.getY2() ? 1 : -1;
 
       for (int c = 0; c < format.outputs; c++) {
-        ((float[]) output)[f * format.outputs] = (float) (line.getX1() + Math.abs(line.getX2() - line.getX1()) * (neg * framesDrawn) / framesToDraw);
-        ((float[]) output)[f * format.outputs + 1] = (float) (line.getY1() + Math.abs(line.getY2() - line.getY1()) * (neg * framesDrawn) / framesToDraw);
+        ((float[]) output)[f * format.outputs] = (float) (line.getX1() + negX * Math.abs(line.getX2() - line.getX1()) * framesDrawn / framesToDraw);
+        ((float[]) output)[f * format.outputs + 1] = (float) (line.getY1() + negY * Math.abs(line.getY2() - line.getY1()) * framesDrawn / framesToDraw);
       }
 
       framesDrawn++;
@@ -52,6 +59,10 @@ public class AudioPlayer extends Thread {
     return lines.get(currentLine % lines.size());
   }
 
+  public static void setRotateSpeed(double speed) {
+    AudioPlayer.ROTATE_SPEED = speed;
+  }
+
   @Override
   public void run() {
     try (XtAudio audio = new XtAudio(null, null, null, null)) {

src/Line.java

@@ -16,16 +16,20 @@ public class Line {
     return Math.sqrt(Math.pow(getX1() - getX2(), 2) + Math.pow(getY1() - getY2(), 2));
   }
 
-  public void rotate(double theta) {
+  public Line rotate(double theta) {
     double x1 = getX1();
     double y1 = getY1();
     double x2 = getX2();
     double y2 = getY2();
 
-    setX1(x1 * Math.cos(theta) - y1 * Math.sin(theta));
-    setY1(x1 * Math.sin(theta) + y1 * Math.cos(theta));
-    setX2(x2 * Math.cos(theta) - y2 * Math.sin(theta));
-    setY2(x2 * Math.sin(theta) + y2 * Math.cos(theta));
+    Line line = new Line(x1, y1, x2, y2);
+
+    line.setX1(x1 * Math.cos(theta) - y1 * Math.sin(theta));
+    line.setY1(x1 * Math.sin(theta) + y1 * Math.cos(theta));
+    line.setX2(x2 * Math.cos(theta) - y2 * Math.sin(theta));
+    line.setY2(x2 * Math.sin(theta) + y2 * Math.cos(theta));
+
+    return line;
   }
 
   public Point getA() {

test/TestSuite.java

@@ -4,10 +4,27 @@ import static org.junit.Assert.*;
 
 public class TestSuite {
   @Test
-  public void lineRotationTest() {
+  public void lineRotationTest1() {
     Line line = new Line(-0.5, 0.5, 0.5, 0.5);
-    line.rotate(Math.PI / 2);
 
+    line.rotate(Math.PI / 2);
     assertEquals(new Line(-0.5, -0.5, -0.5, 0.5), line);
+
+    line.rotate(Math.PI / 2);
+    assertEquals(new Line(0.5, -0.5, -0.5, -0.5), line);
+
+    line.rotate(Math.PI / 2);
+    assertEquals(new Line(0.5, 0.5, 0.5, -0.5), line);
+
+    line.rotate(Math.PI / 2);
+    assertEquals(new Line(-0.5, 0.5, 0.5, 0.5), line);
+  }
+
+  @Test
+  public void lineRotationTest2() {
+    Line line = new Line(-0.5, -0.5, -0.25, 0.5);
+
+    line.rotate(Math.PI / 2);
+    assertEquals(new Line(0.5, -0.5, -0.5, -0.25), line);
   }
 }