attac.us

I found a way to draw 1-bit sketches in TI-BASIC on my calculator using dithering. I used ordered dithering because it is the easiest to implement, and all that is needed on a 96×64 screen. Below is the code I used, with comments.

First, set a 4×4 Bayer matrix to [J].

:[[1,9,3,11][13,5,15,7][4,12,2,10][16,8,14,6]]/17→J

This will clear drawings, but make sure your graphs are also cleared before running this program.

:ClrDraw

Iterate through each pixel in range, from the top left $(0, 0)$ to the bottom right $(94, 62)$.

:For(X,0,94)
:For(Y,0,62)

We are graphing $z$, a function of $x$ and $y$, with a range of $[0, 1]$, where $0$ represents lightness and $1$ represents darkness. Here, I am graphing $z = (x / 94 + y / 62) / 2$.

:((X/94)+(Y/62))/2→Z

Note that matrix indices start at 1 instead of 0 in TI-BASIC. If $z$ is greater than the value of the Bayer matrix at $(x, y)$, the pixel will be displayed in black.

:If Z>[J](remainder(X,3)+1,remainder(Y,3)+1)/17
:Then
:Pxl-On(Y,X)
:End

:End
:End

The program ends here. This is how it came out:

And with more interesting functions, like remainder(X,Y+1)/(Y+1)→Z:

Or even (cos(X^2/400)+cos(Y^2/200)+2)/4→Z:

If you try this out, get ready for long drawing times, as TI-BASIC for the Z80 chipset is extremely slow.