Monday 5 February 2018

First steps towards MEGA BASIC for the MEGA65

It's got late, so just a quick post with some fun screen shots and a video.  I'll do another post another day talking about how I have extended the C64 BASIC tokeniser with proper keywords, as there doesn't seem to be many examples of this that I can find on line.

But for now, we have a demo of the new CANVAS STAMP command.

CANVASes in MEGA BASIC are things you can put graphics on, more precisely, they are screen-like things that you can cover with characters. However, as these are MEGA65 characters, they can be 8x8 blocks where each pixel is specified by an 8-bit palette entry, i.e., you can freely use any of 256 colours in each of these 8x8 blocks. 

Each CANVAS has a size, up to 255x255, and you can have upto 255 of them (you will run out of RAM before then in any case, most likely).

There is also the special CANVAS 0, which is the screen you see. If you STAMP something onto a visible part of CANVAS 0, then it will appear on the screen, e.g., if I do:


This tells MEGA BASIC that I want to draw whatever is in CANVAS 1 onto the screen, beginning at the top left.  You can also STAMP just a part of a CANVAS, but that is too advanced for today.

Notice that I haven't said anything about how to turn on "graphics mode" or pick the right mode etc. That's because you don't need to do that in MEGA BASIC.  The text mode screen is automatically overlain onto CANVAS 0 in real time. There is a raster interrupt that uses a few % of the CPU time to do this each frame, so you can even POKE onto the screen, and it will still magically update and appear together with the graphics.

However, that's all a bit abstract. What we need is to see this in action.

So first we start at the READY prompt for MEGA BASIC. It really is a V0.1 at the moment, with lots of bugs, and most things are not yet implemented.

So lets do that CANVAS STAMP command I mentioned above, to draw the contents of CANVAS 1 (a picture of the MEGA65 logo) onto the screen (CANVAS0):

Oh dear, we can't see part of it, because it is hidden behind the text.  That's okay, because we can just do shift-HOME to rub the text out, and then we can see the full logo behind:

 We could also get a bit more excited and draw three logos, instead of 1:
This ability to seamlessly work with text and graphics using simple commands is very much the philosophy of MEGA BASIC. There will also be commands for easy manipulation of sprites, and most likely also using SID tunes in the standard format that loads at $1000-$1FFF, perhaps with commands like TUNE LOAD "some.sid",8 , TUNE 1 and TUNE OFF.  There will also be CANVAS and SPRITE editors on the MEGA65, as well as cross-platform tools, to suit various needs. Basically if you want to make a nice little game or graphically rich program, it will be super easy and super fun to do.

So lets make something a bit more sophisticated. Right now we don't have those nice editors etc, and it is VERY late, so we will just draw MEGA65 logos randomly on the screen. To do this, we need only four lines of quite understandable BASIC:

And then, pronto, we have logos being drawn all over the screen!
It should also me mentioned that because it is based on characters, the drawing is really quite fast.  You can paste quite a few CANVASes per second, even at 1MHz. And with the FAST command to select 50MHz, you can do even more. Here is a little video (sorry for the bad audio, my microphone is quite sick at the moment) to see it all in action, including stamping many of these big logos on the screen per second:

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