What exactly do Plot and Unplot do?

[Paul]

Yes, I've read this too.
There ist also a rebuilt version of that ROM around with printing dropped and read, data, restore reimplemented by backporting these from the Spectrum.

[Moggy]

The ZX81 ROM was supposed to have...

DATA

DRAW

PRINT TO

READ

RESTORE

UNDRAW

But as mentioned these items were given up for the print routines.

[Freya]

The ZX81 ROM was supposed to have...

DATA

DRAW

PRINT TO

...

PRINT TO sounds really interesting!
Do you know what that command was supposed to do?

[Fruitcake]

You can find details here.

[bola_dor]

A character can also be 4 pixels. a bit like character 129 to 143 on the ZX Spectrum.

PLOT will set the large pixels in a character on the screen.
Since the screen is character based you can't plot a pixel at the position of a character unless the character is the graphical character 0 to 7 or 128 to 135.

UNPLOT will erase the plotted pixel.

But how is this different to using Print AT when you have a char based display file?
I'm wondering what was the point of the plot keyword at all on the zx81.
Couldn't you do exactly the same thing with Print AT?

Freya

when printinting the coordinates increases from top to bottom , left to right. whith plot they increases from the bottom.
you can use prtint at but for any calculated pixel (if you whant to draw a line or cirrcle) you will need to preserve somehow the other three "pixels" involved in that character...


(edited by moderator 1024MAK)

[dr beep]

But how is this different to using Print AT when you have a char based display file?
I'm wondering what was the point of the plot keyword at all on the zx81.
Couldn't you do exactly the same thing with Print AT?

when printinting the coordinates increases from top to bottom , left to right. whith plot they increases from the bottom.
you can use prtint at but for any calculated pixel (if you whant to draw a line or cirrcle) you will need to preserve somehow the other three "pixels" involved in that character...

With PLOT you don't need to calculate the character to be set.
Is there already a plotted point or not?
Ie
pos1 is set and you add pos2. character adds 2
pos1 is set and you add pos4, character adds 134