In text book I am reading it talks about fragment tests that are performed when rendering.

All of these tests talk about comparing the current fragment x value(x be alpha, color ... etc) with their co responding buffer value and do something in case if test passes. Test usually being a comparison between those two >=, <= .. etc.

What I cannot understand is where do these buffer values come from in the first place?

Are these previous values? if so, What do the current values have to do with previously calculated values?

I don't even know what to search in google for this topic. Sorry if it is a total starter question. I am currently reading about rendering for the first time

In the textbook I am reading, it talks about fragment tests that are performed when rendering.

All of these tests involve comparing the current fragment x value  (x can be alpha, color, etc.) with a corresponding buffer value, and doing something in case the test passes. The test is usually a comparison between those two values (for example, >=, <=, etc.).

What I cannot understand is where do these buffer values come from in the first place?

Are these previous values? If so, what do the current values have to do with previously calculated values?

I don't even know what to search in google for this topic. Sorry if it is a total starter question. I am currently reading about rendering for the first time