Locate OS

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Synopsis

Header: fxcg/display.h
Syscall index: 0x1863
Function signature: int locate_OS(int x, int y)

Sets the cursor position for Print_OS.

Parameters

  • x Must be in range of [1,21]
  • y Must be in range of [1,8]

Returns

0 on failure, 1 on success.

Comments

This function does bounds checking; if x or y are out of range, it does nothing, otherwise, it calls Cursor_SetPosition. As the latter function also does bounds checking, it is best to use it directly in order to avoid duplicate checks, achieving better performance.

locate_OS:
	mov     #1, r2
	cmp/ge  r2, r4          ! Is r4 >= 1? If so set T=1
	bf      locate_OS_exit  ! If R4 is less than one do not set the cursor position
	mov     #21, r6
	cmp/gt  r6, r4
	bt      locate_OS_exit  ! Don't set the cursor position if x>21
	cmp/ge  r2, r5
	bf      locate_OS_exit  ! Don't set the cursor position if y<1
	mov     #8, r2
	cmp/gt  r2, r5
	bt      locate_OS_exit  ! Don't set the cursor position if y>8
	mov.l   #Cursor_SetPosition, r2
	add     #-1, r5
	jmp     @r2 ! Cursor_SetPosition
	add     #-1, r4
! ---------------------------------------------------------------------------

locate_OS_exit:
	rts
	nop
! End of function locate_OS