| Routines

22CB: THE 'POINT' SUBROUTINE

This subroutine is called from S_POINT. It is entered with the coordinates of a pixel on the calculator stack, and returns a last value of 1 if that pixel is ink colour, and 0 if it is paper colour.
POINT_SUB | 22CB | CALL STK_TO_BC | y-coordinate to B, x to C.
| 22CE | CALL PIXEL_ADD | Pixel address to HL.
| 22D1 | LD B,A | B will count A+1 loops to get the wanted bit of (HL) to location 0.
| 22D2 | INC B
| 22D3 | LD A,(HL)
POINT_LP | 22D4 | RLCA | The shifts.
| 22D5 | DJNZ POINT_LP
| 22D7 | AND $01 | The bit is 1 for ink, 0 for paper.
| 22D9 | JP STACK_A | It is put on the calculator stack.