Ask HN: How to draw a single pixel? | Hacker News Reader

Ask HN: How to draw a single pixel?

4 pointsgsivil8 comments

This question is maybe an echo from the eighties, but I am interested to find resources so as to draw a single pixel on the terminal. If I could change the state of one pixel then it would be just math to go from pixel to lines and from lines to curves and from curves to shapes.

If I am not mistaken one of the important steps is to activate the so called video mode and not the text mode. Reading a bit about that I guess I have to access the memory buffer and modify individual chunks of memory. I cannot estimate how difficult this can be.

I know that there are libraries to let you do that on another window and of course to let you create images. Creating SVG pictures is rather trivial for example. I am interested to learn my self how to go in that level than to use a library.

I would be grateful to find resources for that and preferably in the following languages. Common Lisp > Python > C.

Feel free to ignore my question since it is driven by curiosity to hack and not from urgent need for productivity.

Must you make me jog back such old memories? (Well actually, Thank you :-))

FWIW, this is how we used to do it in BASIC, C and MASM in the good ol' DOS days, back in the 80s; hope it can give you at least some conceptual confirmation + insight:

You wrote:

> activate the so called video mode and not the text mode

Spot on.

> access the memory buffer and modify individual chunks of memory

Spot on again. Unless I'm forgetting something, DOS used to reserve a chunk of RAM (that they called 'lower memory') as video RAM. We used to 'peek' and 'poke' bytes directly to this (at mem segment 0800:0000Hex or something). Of course, that was on CGA display adapters, and under DOS. With today's SVGA and whatnot + Ubuntu, a lot of these specifics would change but I'm afraid I won't be able to help you with all that - been a while (about 2 decades) since I could last indulge into that sort of hacking.

Well, best wishes from an ancient hacker - may you keep at it for as long as you wish to.

Read the manual page about "vga_drawpixel" function. I'm not sure you can use this if you run under X. Here is a useful link:

http://linux.die.net/man/3/vga_drawpixel

You should probably use a more advanced graphics library like the one provided by Gnome, but if you want to learn how to do it from scratch I suppose you need to start from a text mode Linux installation.

Well, it pretty much depends on what system you are using. On linux for example you could use frame buffers (on windows or osx i have no idea). But i think you should check out some kind of library like SDL, which is easy to use and has bindings for common lisp and python (it's written in C).

EDIT: take a look to http://code.google.com/p/lispbuilder/wiki/LispbuilderSDL

Are you running under Windows, OS X, Linux, something else?

And if you're running Linux, which window manager are you running?

I am running Linux (ubuntu 10.10) and I am using the Gnome terminal. Of course I could switch to something else if this could make things easier.

You cannot draw graphics in a terminal window (he says, half-expecting to be corrected).

Your program can open up a window of its own and draw graphics in that.

Or you can do the low level thing on a different virtual console using Linux's framebuffer support (see the svgalib link octopus posted above) (as an aside, press Ctrl+Alt+F2, observe what happens, then Alt+F7 to return here).

> You cannot draw graphics in a terminal window (he says, half-expecting to be corrected).

Depends on the terminal. xterm has a "tektronix mode" to emulate the old Tektronix 4014 graphic terminal. This has a 4096x4096 coordinate system for vector graphics. Most other terminals do not emulate this, of course.

http://en.wikipedia.org/wiki/Tektronix_4010

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