The BBC and Master Computer Public Domain Library

AC0E POINT(

Submitted by Steve Fewell

Description:

Call routine &96AF to get the Integer value of the expression after the POINT( keyword (issue Type mismatch error if
the result is a String value)
Push the Integer to the BASIC Stack. This is the first parameter to the POINT routine - i.e. the X screen position.

Read the comma ',' character, and issue 'Missing ,' error if the next non-space character wasn't a comma.
Call routine &96A7 to obtain the Integer value of the expression after the comma and check for a closing parenthesis ')'.
Issue a 'Syntax error' if the closing bracket wasn't found.
Push this Integer's LSB (&2A) to the 6502 Stack, and the 16-bit Integer's MSB (&2B) to the X index register.
These 2 bytes are the second parameter to the POINT routine - i.e. the Y screen position.

Retrieve the first Integer from the BASIC stack.
Store the Second Integer MSB (from X) to location &2D and store the second Integer LSB (retrieved from 6502 Stack)
to location &2C.

Set Y to 0 and X to #&2A -> as &002A is the start of the 5-byte OSWORD parameter block, which contains the
following:
* Byte &2A -> The X screen position LSB
* Byte &2B -> The X screen position MSB
* Byte &2C -> The Y screen position LSB
* Byte &2D -> The Y screen position MSB
* Byte &2E -> Reserved for return value

Call the OSWORD &09 command to execute the POINT instruction.
If the return value (byte &2E) is negative then exit with the IWA = -1 (TRUE); otherwise, exit with the IWA = byte &2E
(which should be 0, so the IWA will be set to FALSE).

Disassembly for the POINT( routine