Thankfully, I have one of the old calcs with 128KB mem. But a 95*63 Change counter is missing a crucial element: What commands changed that pixel.

The tricky thing is that if you draw a line or a rectangle or whatever, you are going to overwrite something else, and by simply erasing it, you won't be undoing it

Quick question, you said that this program has three or four eight set in tools to use to draw right? What are they?

Edit:
Sorry if this has already been asked, if it has I missed it.

Edit:
The reason I'm asking is because I can see two, feasible, possibilities for a TI-BASIC undo button.

1. Each time you use a command you store the coordinates needed and the type of action it was (I personally would store the coordinates and then make the type of action a different decimal place for each one) and when you run out of elements, if you do, just archive the current one and overflow into a new list. Then when you use the undo button you simply clear the screen and redraw it by using the stored coordinates and commands. Slower, yes, but would probably be the best option if you want as many undoes as you can.

2. After each command you store the image to a different picture variable, then when the click undo it just clears the screen and recalls the previous saved image. This is probably the fastest but as people have said you're only limited to ten (unless you use the hacked picture variables but I'd advise against that for something like this).

There are other ways you can do it but they are way over kill and very convoluted. And also would be way harder to code.

Ah ok, Well then that actually makes the first option I gave a lot easier and potentially faster than I thought it would be.

It actually would be pretty simple to implement, especially if you're only going to make it a one list cap on the amount of content.

Edit:
Also depending on how you store your data, but it still should be easy.

Edit:
What Window settings are you using? (Xmin=0, Xmax94, Ymin=-62, Ymax=0?)

What do you mean? Like I understand the y-value thing, just not the thing about the x-coordinates.

BTW, for a 95x63 matrix, store it as 10 pictures, considering that you can restrict yourself where each entry has a integer maximum of 1000.
If I recall this costs somewhere around 7600 bytes.

Of course, if you don't expect the user to paint the same pixel hundreds of times, you can reduce the number of pictures.


Previous example rehashed:

Onscreen
OOOOO
*O*O*
**O**
*O*O*
OOOOO

In layer 1
*OOO*
*O*O*
*****
*O*O*
*OOO*

In layer 2
O***O
*****
**O**
*****
O***O

if a pixel is written over 3 times, then it will be in both layer 1 and layer 2; if 4 times, layer 4, etc.

Quote from: Freyaday on February 27, 2011, 05:32:55 pm

The formula I'm using is 100V+X+.01Y

What formula is that? (By the way, it can be one byte smaller if you do VE2+X+.01Y.

And a byte smaller if you do VE2+X+sub(Y.