The ClearIconsScanner subroutine - The Sentinel on the BBC Micro

       Name: ClearIconsScanner                                       [Show more]
       Type: Subroutine
   Category: Scanner/energy row
    Summary: Clear the energy icon and scanner row at the top of the screen
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ClearScreen calls ClearIconsScanner
             * ShowGameOverScreen calls ClearIconsScanner


.ClearIconsScanner

 LDA #0                 \ Set xIconCounter = 0 so we start drawing from the left
 STA xIconCounter       \ edge of the screen

.enec1

 LDA #0                 \ Draw a blank icon into the top part of the screen (via
 JSR DrawIcon           \ the icon screen buffer at iconBuffer) and move along
                        \ to the right, incrementing xIconCounter as we do

 LDA xIconCounter       \ Loop back to keep drawing blank icons until we have
 CMP #40                \ cleared column 39, at which point we have cleared the
 BCC enec1              \ entire row

 JMP ShowIconBuffer     \ Display the contents of the icon screen buffer by
                        \ copying it into screen memory, which will clear the
                        \ row on-screen, and return from the subroutine using a
                        \ tail call

[X]

Subroutine DrawIcon (category: Scanner/energy row)

Draw a single icon in the top-left corner of the screen (via the icon screen buffer at iconBuffer) and move along to the right

[X]

Subroutine ShowIconBuffer (category: Screen buffer)

Display the redrawn icon and scanner row by copying the contents of the icon screen buffer into screen memory

[X]

Label enec1 is local to this routine

[X]

Variable xIconCounter in workspace Main variable workspace

A counter for drawing the icons in the top-left of the screen that show the player's energy level, as we work from left to right along the x-axis

Scanner/energy row: ClearIconsScanner