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Building a Tetris Clone in X86 Assembly, Pt. Ⅰ: Hello, World

71 points| raphaelss | 10 years ago |cmcenroe.me

13 comments

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cjauvin|10 years ago

It's not 100% related but I had great fun building a very minimal Tetris clone in 6502 assembly, for the C=64, a couple of years ago (the code is "kinda" commented):

https://github.com/cjauvin/tetris-464

akkartik|10 years ago

Is anybody able to get the repo running? 'make qemu' simply shows a blank screen and exits. But the repo seems much farther along than the blog post.

programble|10 years ago

The build defaults to debug, so `make qemu` also starts QEMU waiting for a debugger to attach. `make qemu BUILD=release` won't.

pki|10 years ago

there's no comment section there so i'd figure i'd ask here: what is that font that it outputs? is that part of BIOS or something? or part of boot loader or PXE server?

i assumed asm was the lowest level, is there some builtin font by default that can't be changed or something?

jquast|10 years ago

The default video bios mode is used as-is here, https://en.wikipedia.org/wiki/Video_BIOS

There is no terminal emulator here. This hello world text is written directly to video memory -- and yes, there is a character rom, so placing a string of words in memory OR'd with bits set for video attributes (the #defines there) make it color.

programble|10 years ago

It is indeed the default BIOS font. You usually get it when switching to a TTY on Linux, as well.

cnvogel|10 years ago

Its part of the hardware (emulated by qemu). A VGA card (or any other text mode capable video adapter) will use either a portion of ROM or some part of video memory to hold the font from where its accessed simultaneously to the beam drawing the CRT screen. (Hercules, CGA, EGA, VGA all did this).

In contrast to this, many Unix workstations never implemented such a thing and went directly to graphics framebuffers (SUN cgX framebuffers for the ... Sbus??). For that, of course you have to implement the font rendering in "bios" , or in the case of the sun machine in the OpenFirmware. Slowly.)

thinkpad20|10 years ago

I haven't read through the tutorial, but I would assume that the programmer does not specify the fonts being used, but rather outputs bytes to stdout. It's the terminal emulator that's running the program that is responsible for displaying those bytes, so that's where things like font would be set.