Maths (Arithmetic): PIX1

       Name: PIX1                                                    [Show more]
       Type: Subroutine
   Category: Maths (Arithmetic)
    Summary: Calculate (YY+1 SYL+Y) = (A P) + (S R) and draw stardust particle
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * STARS1 calls PIX1
             * STARS2 calls PIX1
             * STARS6 calls PIX1


 Calculate the following:

   (YY+1 SYL+Y) = (A P) + (S R)

 and draw a stardust particle at (X1,Y1) with distance ZZ.


 Arguments:

   (A P)                A is the angle ALPHA or BETA, P is always 0

   (S R)                YY(1 0) or YY(1 0) + Q * A

   Y                    Stardust particle number

   X1                   The x-coordinate offset

   Y1                   The y-coordinate offset

   ZZ                   The distance of the point (further away = smaller point)


.PIX1

 JSR ADD                ; Set (A X) = (A P) + (S R)

 STA YY+1               ; Set YY+1 to A, the high byte of the result

 TXA                    ; Set SYL+Y to X, the low byte of the result
 STA SYL,Y

                        ; Fall through into PIX1 to draw the stardust particle
                        ; at (X1,Y1)