package graphics;

public class MatrixStack
{
  private static final int STACK_SIZE = 100;
  private int sp = -1;
  private Matrix3D[] stack;

  //start off the matrix stack with a single identity matrix
  public MatrixStack()
  {
    stack = new Matrix3D[STACK_SIZE];

    sp = 0;
    stack[sp] = new Matrix3D();
    stack[sp].identity();
  }

  public int size()
  {
    return sp+1;
  }

  public boolean empty()
  {
    return (size() == 0);
  }

  public void push()
  {
    if (sp >= STACK_SIZE)
    {
      System.err.println("Cannot push onto stack - stack is full!");
      return;
    }

    //copy from the top of the stack and push
    Matrix3D m = new Matrix3D();
    m.copy(stack[sp]);

    sp++;
    stack[sp] = m;
  }

  public Matrix3D pop()
  {
    if (empty())
    {
      System.err.println("Cannot pop stack - stack is empty!");
      return null;
    }

    sp--;
    return stack[sp+1];
  }

  //return matrix at the top of the stack
  public Matrix3D peek()
  {
    return stack[sp];
  }
}