id Software's Command Keen 4 starts up with this cool intro sequence where the words "COMMANDER KEEN" scroll by in the background with what appears to be a transparency effect. I was curious how this was done. - ThreadSky

gloriouscow.bsky.social • 1 day ago

id Software's Command Keen 4 starts up with this cool intro sequence where the words "COMMANDER KEEN" scroll by in the background with what appears to be a transparency effect.

I was curious how this was done.

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nivrig.bsky.social•12 hours ago

every amiga coder: [nods]

:)

gloriouscow.bsky.social•12 hours ago

If i had a cooler childhood maybe I'd be writing an Amiga emulator instead

nivrig.bsky.social•11 hours ago

There's a niche need for non-GPL Amiga emulator, if you get around to it :)

gloriouscow.bsky.social•11 hours ago

I am powered solely by caffeine and nostalgia. Take either away and I can't accomplish much.

nivrig.bsky.social•11 hours ago

gloriouscow.bsky.social•1 day ago

Scrolling around in 4bpp mode, we quickly see a block of black and white.

I smell font.

gloriouscow.bsky.social•1 day ago

This isn't a little font either, as making the window narrower just scrambled everything worse. So, let's make the window wider...

gloriouscow.bsky.social•1 day ago

Ok, so a bit anticlimactic. No clever tiling system in play here - just literally bigass fonts.

These are really 1bpp, but i'm looking at them as 4bpp so there's a bit of color fringing that isn't really there.

gloriouscow.bsky.social•1 day ago

How is the transparency effect done? Well, it's basically done for free by the EGA hardware. By writing a 1bpp bitmap into a plane, we set one bit in the resulting 4bpp pixel. If the word "commander" is binary 10, and the word "keen" is 01, we can set 10 and 01 to the same gray color.

gloriouscow.bsky.social•1 day ago

Their intersection where the words are set in both planes, will have the value 11, which can be set to a brighter color, producing the transparency effect.

gloriouscow.bsky.social•1 day ago

Peering into a planar video mode like this is interesting. In the VRAM window we can only see one plane at a time, the top of a stack of four planes, if you will. So everything appears as if we were playing the game in black and white.

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