Commander X16

On 1/22/2022 at 6:53 PM, Edmond D said:

The screen ram on the X16 has to be accessed via a VPOKE command in BASIC. While that works, it isn't rather intuitive, unlike the old Commodore system where the screen was a grid with a fixed starting address and byte wise characters and a separate colour area, again byte wise with a fixed address. 



While the VERA is an amazing piece of hardware, programming for it isn't as straight forward as the old machines, most likely given its power and the fact that it's access through I/O space. In addition the character and colour grid are 'interwoven' where  it's character location 1 (top left of screen), colour location 1, character location 2, colour, ... Another factor is the between the top line and the next line are addresses that aren't contagious. I meant to type contiguous ?



The VPOKE command  is  VPOKE <bank>, <address>, <value>  which makes sense to those who know both the screen layout and the VERA memory map. In my programming I've got lines like VPOKE 0,(Y+5)*256+(X-2)*2, 002  which isn't extremely readable. Without typing it in can anyone easily tell whats' being set and where - character data or colour? 



What I propose is a different command to put characters on the screen that would make sense for a very novice programmer in BASIC:



SPOKE <X>, <Y>, <"CHAR">,<FG Colour>,<BG Colour>



Here the X and Y positions are very clear; the topmost left location has a value of 1 and 1 respectively. The character to set would be the first (hopefully only) character of string variable, since all theses don't have any control codes. The colour for foreground and background would be integers. A command like:



SPOKE 12, 5, "A", 4,6



Would put a red A with a blue background on the fifth line,  twelve charters from the left of the screen. It would be just that simple!



Beyond being understandable, the math for calculating exactly where the bytes (char, plus colours) need to be stored isn't in the realm of BASIC math (and its slowness.)



I've kept this simple, avoiding the two layers, since it's meant to be a very basic BASIC command aimed at the beginner programmer. Once they've mastered it, if they need to move into VPOKE and VERA they can do so.

On 1/22/2022 at 7:53 PM, Edmond D said:

Here the X and Y positions are very clear; the topmost left location has a value of 1 and 1 respectively.

On 1/22/2022 at 8:31 PM, Ed Minchau said:

That should be 0,0.

On 1/22/2022 at 7:39 PM, TomXP411 said:

Yes, cursor positioning is sorely needed. The ideal implementation would be LOCATE, similar to Advanced BASIC and BASIC 7. 



I have added a feature request on the ROM git repo at https://github.com/commanderx16/x16-rom/issues/227