Skip to main content

Ralsina.Me — Roberto Alsina's website

CobraPy: baby steps

Some con­text: I am do­ing a sort of mod­ern retro-pro­gram­ming en­vi­ron­men­t-thingie.

So ... I caved. I caved and start­ed typ­ing.

It's still just ex­plorato­ry, fool­ing around, but I want­ed to see whether the vague ideas I had about how this could, maybe work were right, and hey, they are!

Text Mode

I want­ed a text mod­e. Some­thing with N rows and M col­umns where you could just say "put this text there". Done. In the most ba­sic pos­si­ble way that work­s.

Implemented a print_at function that takes row, column and text, and does what it says in the label.

Immediate Graphics Mode

In these old com­put­ers you could just draw in the graph­ics mem­o­ry. In 2020 ... not so much. So, I im­ple­ment­ed a sort of off­screen buf­fer. You draw there, and it gets blit­ted a lot to screen. Ends up work­ing like a flick­er-free dou­ble-buffered screen! Nice!

Implemented ellipse which ... draws an ellipse. I know, surprising.

Interpreter / Prompt

It would not be 80s-­like if you could not do those things in­ter­ac­tive­ly. So, yes, you can.

Now that was in­ter­est­ing. you see, nowa­days you are sup­posed to have an event loop. The com­put­er is there, idling and when some­thing hap­pen­s, then it does some­thing. So, you clicked? It re­act­s. 10 mil­lisec­onds passed? It does its thing.

In the 80s it was not like that. Your pro­gram start­ed and it owned the ma­chine. It went through your code, run­ning it as fast as it could with its lit­tle two-mega­herz-­heart un­til it ran out of code and then it was done.

So, how to make it act like that?

  • Start the event loop.
  • Start a sec­ond thread with a promp­t.
  • Have the us­er in­ter­act with the promp­t.
  • When the user presses Enter ... send the command to the event loop via a queue.
  • When the event ar­rives, do the thing.

And yes, it work­s! It's prob­a­bly hor­ri­ble for per­for­mance, but it does work just fine, and it's much, much eas­i­er to make a work­ing pro­gram fast than it is to make a fast pro­gram work.

So, what's nex­t?

The Future

I may try to in­te­grate the prompt and the win­dow where the text and such is dis­played (right now it's in a ter­mi­nal) ... maybe sprites.

Af­ter that:

  • Make the API nice and use­ful (a few weeks of work)
  • Make the thing run well (a few days of work)
  • Do the jan­i­to­ri­al work to make it us­able by some­one else (a cou­ple days of work)
  • Sup­port it, doc­u­ment it, etc (8 to 30 years of work)

The Nerdy Details

  • To do the graph­ics I am us­ing py­glet
  • To do off­screen draw­ing I am us­ing Pil­low
  • Tool­ing in­cludes the usu­al sus­pect­s: Python 3.8, po­et­ry, pylin­t, flake8
  • Code (all 50 lines or so!) in GitHub

Yes, this means this "80s" thing is ac­tu­al­ly mul­ti­thread­ed hard­ware-ac­cel­er­at­ed OpenGL graph­ic­s. I know, I know.


Contents © 2000-2020 Roberto Alsina