add initial methods

src/com/blarg/gdx/graphics/BillboardSpriteBatch.java

@@ -1,5 +1,10 @@
 package com.blarg.gdx.graphics;
 
+import com.badlogic.gdx.graphics.g2d.TextureRegion;
+import com.badlogic.gdx.graphics.g3d.decals.Decal;
+import com.badlogic.gdx.graphics.g3d.decals.DecalBatch;
+import com.badlogic.gdx.utils.Array;
+
 /***
  * <p>
  * Wrapper over libgdx's included {@link DecalBatch} with automatic easy management of
@@ -8,5 +13,74 @@ package com.blarg.gdx.graphics;
  * </p>
  */
 public class BillboardSpriteBatch {
+	static final int CAPACITY_INCREMENT = 128;
 
+	Array<Decal> sprites;
+	int pointer;
+	boolean hasBegun;
+	DecalBatch decalBatch;
+
+	public BillboardSpriteBatch() {
+		sprites = new Array<Decal>(true, CAPACITY_INCREMENT, Decal.class);
+		pointer = 0;
+		addNewSprites(CAPACITY_INCREMENT);
+
+		hasBegun = false;
+		decalBatch = null;
+	}
+
+	public void begin(DecalBatch decalBatch) {
+		if (hasBegun)
+			throw new IllegalStateException("Cannot be called within an existing begin/end block.");
+		if (decalBatch == null)
+			throw new IllegalArgumentException();
+
+		this.decalBatch = decalBatch;
+		hasBegun = true;
+		pointer = 0;
+	}
+
+	public void flush() {
+		if (!hasBegun)
+			throw new IllegalStateException("Cannot call outside of a begin/end block.");
+
+		// TODO: render decals with DecalBatch
+
+		pointer = 0;
+	}
+
+	public void end() {
+		if (!hasBegun)
+			throw new IllegalStateException("Must call begin() first.");
+
+		flush();
+
+		hasBegun = false;
+		decalBatch = null;    // don't need to hold on to this particular reference anymore
+	}
+
+
+	private void increaseCapacity() {
+		int newCapacity = sprites.items.length + CAPACITY_INCREMENT;
+		sprites.ensureCapacity(newCapacity);
+		addNewSprites(CAPACITY_INCREMENT);
+	}
+
+	private void addNewSprites(int count) {
+		for (int i = 0; i < count; ++i)
+			sprites.add(Decal.newDecal(new TextureRegion()));
+	}
+
+	private int getRemainingSpace() {
+		return sprites.size - pointer;
+	}
+
+	private Decal nextUsable() {
+		if (getRemainingSpace() == 0)
+			increaseCapacity();
+
+		Decal usable = sprites.items[pointer];
+		pointer++;
+		return usable;
+	}
 }