Controllers: TT17

       Name: TT17                                                    [Show more]
       Type: Subroutine
   Category: Controllers
    Summary: Scan the key logger for the directional pad buttons
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * Main game loop (Part 5 of 6) calls TT17


 X and Y are integers between -1 and +1 depending on which buttons are pressed.

 This routine does a similar job to the routine of the same name in the BBC
 Master version of Elite, but the code is significantly different.


 Returns:

   A                    The button number, icon bar button was chosen

   X                    Change in the x-coordinate according to the directional
                        keys being pressed on controller 1

   Y                    Change in the y-coordinate according to the directional
                        keys being pressed on controller 1


.TT17

 LDA QQ11               ; If this is not the space view, jump to dpad1 to read
 BNE dpad1              ; the directional pad on controller 1

 JSR DOKEY              ; This is the space view, so populate the key logger
                        ; and apply the docking computer manoeuvring code

 TXA                    ; Transfer the value of the key pressed from X to A

 RTS                    ; Return from the subroutine

.dpad1

 JSR DOKEY              ; Populate the key logger and apply the docking computer
                        ; manoeuvring code

 LDX #0                 ; Set the initial values for the results, X = Y = 0,
 LDY #0                 ; which we now increase or decrease appropriately

 LDA controller1B       ; If the B button is being pressed on controller 1,
 BMI dpad5              ; jump to dpad5 to return from the subroutine, as the
                        ; arrow buttons act differently when B is also pressed

 LDA controller1Left03  ; If the left button on controller 1 was not being held
 BPL dpad2              ; down four VBlanks ago or for the three VBlanks before
                        ; that, jump to dpad2 to skip the following instruction

 DEX                    ; The left button has been held down for some time, so
                        ; decrement the x-delta in X

.dpad2

 LDA controller1Right03 ; If the right button on controller 1 was not being held
 BPL dpad3              ; down four VBlanks ago or for the three VBlanks before
                        ; that, jump to dpad3 to skip the following instruction

 INX                    ; The right button has been held down for some time, so
                        ; increment the x-delta in X

.dpad3

 LDA controller1Up      ; If the up button on controller 1 is not being pressed,
 BPL dpad4              ; jump to dpad4 to skip the following instruction

 INY                    ; The up button is being pressed, so increment the
                        ; y-delta in Y

.dpad4

 LDA controller1Down    ; If the down button on controller 1 is not being
 BPL dpad5              ; pressed, jump to dpad5 to skip the following
                        ; instruction

 DEY                    ; The down button is being pressed, so decrement the
                        ; y-delta in Y

.dpad5

 LDA iconBarKeyPress    ; Set A to the key logger entry for the icon bar button
                        ; press, to return from the subroutine

 RTS                    ; Return from the subroutine