BritLion's Putchars

[compiuter]

Question for Britlion or others:
I see You use this in your code

Code:

SUB paint (x as uByte,y as uByte, width as uByte, height as uByte, attribute as ubyte)
    asm
    ld      a,(IX+7)   ;ypos

And I ask about the maneuver you had to know that in (IX+7) is ypos?
I know in fastcall you read in the registers hl de ... the arguments sends by fastcall. But you use IX register. Can you explain me about this. I believe you use similar method by fastcall in the sub function.
Thx.