tandy put their sound chip on the 1A interrupt?

[foone@digipres.club]

@Ongion I've not, no. It sounds awesome, but sadly it doesn't seem it's usable for my usual ancient-software-reversing tasks

[foone@digipres.club]

it's in a function I already found, temporarily named "blit_related".

I guess they don't decode the image until RIGHT before it needs to go up on the screen!

[foone@digipres.club]

if definitely decompresses and then blits the image as two parts, which aren't evenly sized, and it starts from the bottom

[foone@digipres.club]

I think they're just trying to keep their RAM usage down by not having both halves in memory at once

[rakslice@mastodon.social]

@foone this sounds like a job for whatever scripting the debugger supports?

[foone@digipres.club]

@rakslice
new side project: add scripting to this debugger

[foone@digipres.club]

wait is this image format vertically interlaced!?

[foone@digipres.club]

It loads the half-width version, then a few functions later, it's been replaced with a full-width version.
Strange!

[foone@digipres.club]

wait no, the colors are wrong... I bet I'm seeing it decompress the binary, but that's using the full width of the bytes. it then gets expanded out to a 16-color image.

[foone@digipres.club]

well the good news is that I think I've found the decompress_image function. the bad news is that now I have to reverse engineer it

[foone@digipres.club]

it's currently doing the obvious thing for a decompressor to do:
write the byte 04 every 69 bytes

[foone@digipres.club]

oh sweet jesus, that's the left two pixels of the image.
it's loading the image vertically!

at least it's top to bottom.

[foone@digipres.club]

yeah, doom did that too, but Doom was a 2.5D image that had to do pseudo-raycasting.

THIS GAME DOES NOT

[lethal_guitar@mastodon.social]

@foone it's the most efficient way to render images in planar EGA/VGA video modes. So clearly that's what you need to use for a game that's mostly static screens

[foone@digipres.club]

@lethal_guitar yeah. I guess it's faster to draw, but given that it's static scenes... The disk access is gonna take longer!

[foone@digipres.club]

it allocates a 1024 byte buffer, then makes a pointer to the end of it, minus -0x42?

why would you need a link to the end of a new, freshly cleared buffer, minus 62?

[foone@digipres.club]

I think the memory allocation system here is that every malloc returns 2 extra bytes, which is a pointer to the previous block.
unless it's an odd number, in which case it's a free block. and pointer to the previous block, once you make it even again

[foone@digipres.club]

I hate dealing with the internals of memory allocation systems. I prefer to leave that to smarter people than me

[foone@digipres.club]

You see this little About dialog box? Guess how many times the DrawText function is called?

Once! and just to draw "Where in the World is Carmen Sandiego?".
The rest of the text is draw elsewhere, and I have no idea why.

[foone@digipres.club]

correction: it calls it once to draw "Where in the World is Carmen Sandiego?" but that's unrelated to the one on screen WHAT?