| Routines

08907: 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 | 08907 | CALL STK_TO_BC | y-coordinate to B, x to C.
| 08910 | CALL PIXEL_ADD | Pixel address to HL.
| 08913 | LD B,A | B will count A+1 loops to get the wanted bit of (HL) to location 0.
| 08914 | INC B
| 08915 | LD A,(HL)
POINT_LP | 08916 | RLCA | The shifts.
| 08917 | DJNZ POINT_LP
| 08919 | AND 1 | The bit is 1 for ink, 0 for paper.
| 08921 | JP STACK_A | It is put on the calculator stack.