Added parallax, started documentation

doc/index.md

@@ -0,0 +1,25 @@
+# Function Overview
+
+This document intended to assist developers who seek to extend the game by modifying source code in src/.
+
+## Classes
+
+### BackgroundImage
+
+Its constructor takes the following arguments:
+
+`int x, int y, BufferedImage backgroundImage, int width, int height, int parallaxRatio`
+
+Draws a background image that moves one pixel every `parallaxRatio` pixels when `BackgroundImage.draw()` is called.
+
+### Camera
+
+placeholder
+
+## Utility Functions
+
+These functions are located in the `public final` class UtilityFunction; please note that the UtilityFunction constructor is private to prevent initialization.
+
+### readFromFile
+
+placeholder

src/BackgroundImage.java

@@ -4,22 +4,21 @@ import java.awt.image.BufferedImage;
 public class BackgroundImage {
     public int x, y;
     public int width, height;
+    public int parallaxRatio;
     public BufferedImage backgroundImage;
 
-    public BackgroundImage(int x, int y, BufferedImage backgroundImage, int width, int height) throws SpriteException {
-        int compressionRatio;
-
+    public BackgroundImage(int x, int y, BufferedImage backgroundImage, int width, int height, int parallaxRatio) {
         this.x = x;
         this.y = y;
         this.width = width;
         this.height = height;
 
         this.backgroundImage = backgroundImage;
-        // compressionRatio = Math.max(backgroundImage.getWidth() / width, backgroundImage.getHeight() / height);
-        // this.backgroundImage = backgroundImage.getSubimage((backgroundImage.getWidth() - width)/2,
-        //         (backgroundImage.getHeight() - height)/2, width, height);
+        this.parallaxRatio = parallaxRatio;
     }
     public void draw(Graphics g){
-        g.drawImage(backgroundImage, x, y, width, height, null);
+        g.drawImage(backgroundImage, x-GamePanel.camera.x/parallaxRatio % width, y, width, height, null);
+        // added to prevent the background image from disappearing
+        g.drawImage(backgroundImage, x-GamePanel.camera.x/parallaxRatio % width + width - 1, y, width, height, null);
     }
 }