public Ponto verificaZBuffer(Ponto p, int x, int y){
		Ponto retorno = null;
		if(x >= this.zBuffer.length || y >= this.zBuffer[0].length || x < 0 || y < 0){
			return null;
		}
		if(p.getZ() < this.zBuffer[x][y]){
			this.zBuffer[x][y] = p.getZ();
			retorno = p;
		}		
		return retorno;
	}