Do I have to pay taxes in Spain if I don't have residency in the country?

I have now obtained a residency status in Spain, just to avoid the hassle of obtaining a tourist visa, however, the maximum time I would spend in Spain, would never exceed 4 months in a year (including interrupted visits). My question, what triggers the need to pay income tax as a resident? Is it the residency status or the duration of my stay? For example, some say that you need to pay income tax on all your world wide income, if you stay in Spain more than 181 days (6 months) regardless of having a residency status or not, others would say, as long as you have a residency status then you are under the spanish tax laws, regardless how long you stay in Spain. If the second is true, then I better avoid all that, and just get a normal tourist visa and forget about the residency all together. Having a residency status, does it mean I am obliedged to file an income tax for all my earnings world wide, regardless how long I stay in Spain?