Drawing lines: DrawJoystickCross

       Name: DrawJoystickCross                                       [Show more]
       Type: Subroutine
   Category: Drawing lines
    Summary: Draw a cross in the joystick position display (indicator 8 or 10)
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * UpdateIndicator (Part 14 of 15) calls DrawJoystickCross


 This routine draws a cross, relative to a centre point of (80, 216), and with
 a 3-pixel horizontal bar and a 5-pixel vertical bar.


 Arguments:

   A                    Drawing mode:

                          * 0 = Draw (using OR logic)

                          * 128 = Erase (using EOR logic)

   xJoyCoord            The current joystick x-coordinate

   yJoyCoord            The current joystick y-coordinate


.DrawJoystickCross

 STA N                  \ Store the drawing mode in N

                        \ First we draw the 3-pixel horizontal line right from
                        \ (79 + x, 216 + y)

 LDA yJoyCoord          \ Set H = yJoyCoord
 STA H

 LDA xJoyCoord          \ Set joyCoord = xJoyCoord + 79
 CLC                    \
 ADC #79                \ to get the x-coordinate of the left end of the
 STA joyCoord           \ horizontal line at 79 + x

 LDA #216               \ Set W = 216, the y-coordinate of the centre point, so
 STA W                  \ we draw the line from a y-coordinate of 216 + y

 LDA #0                 \ Set S = 0, to denote that joyCoord is the
 STA S                  \ x-coordinate, so we draw the line from point
                        \ (joyCoord, H + W)

 LDA #3                 \ Set T = 3, so we draw a horizontal 3-pixel line
 STA T

 LDA #1                 \ Set U = 1, so the line is 1 pixel high
 STA U

 JSR DrawOrthoLine      \ Draw the horizontal part of the cross, starting from
                        \ (79 + x, 216 + y) and drawing to the right for three
                        \ pixels

                        \ Now we draw the 5-pixel vertical line down from
                        \ (80 + x, 214 + y)

 LDA xJoyCoord          \ Set H = xJoyCoord
 STA H

 LDA yJoyCoord          \ Set joyCoord = yJoyCoord + 214
 CLC                    \
 ADC #214               \ to get the y-coordinate of the top end of the vertical
 STA joyCoord           \ line at 214 + y

 LDA #80                \ Set W = 80, the x-coordinate of the centre point, so
 STA W                  \ we draw the line from an x-coordinate of 80 + x

 LDA #128               \ Set S = 128, to denote that joyCoord is the
 STA S                  \ y-coordinate, so we draw the line from point
                        \ (H + W, joyCoord)

 LDA #1                 \ Set T = 1, so the line is 1 pixel wide
 STA T

 LDA #5                 \ Set U = 5, so we draw a vertical 5-pixel line
 STA U

 JSR DrawOrthoLine      \ Draw the vertical part of the cross, starting from
                        \ (80 + x, 214 + y) and drawing down for five pixels

 RTS                    \ Return from the subroutine