Lemmings, or how clever tricks make platforms more different than they seem #Games #Graphics
Scali’s OpenBlog compares the Amiga, the Atari ST and PC version of the game Lemmings. More specifically, concentrate on the VGA version of Lemmings for PC. There are three machines that have roughly similar video capabilities. All three machines have a video mode of 320×200, and support a palette that can be user-defined by RGB values.
But then we get to the part that kicked this off in the first place: the font. On the Amiga we see a very detailed font, using various shades of green. On the Atari ST, we see a font that looks the same, at first glance. On the ‘lo’ VGA version, we see a font with the same basic shape, but it appears to only have two shades: one green and one white.
The ‘hi’ VGA version however, looks different. For some reason, the font is not as high. Instead of the font filling out the entire area between the level view and the icon bar, there are 4 black scan lines between the level and the font. The icons are the same size and in the same position on screen, so effectively the font is scaled down a bit. It is only 11 pixels high, where the others are 15 pixels high. The font has more shades of green here: a number of 4 in total. Still less than on the Amiga (I count 7 shades there) and Atari ST (5 shades).
Because VGA is not synchronized to the system clock, it is not trivial to change the palette at a given place on screen. While it is possible (see also my 1991 Donut), it will require some clever timer interrupts and recalibrating per-frame to avoid drift. So that explains why they chose to only do this on high performance PCs. On a slow PC, it would slow down the game too much. It also explains why there are 4 black scan lines between the level and the font. Firstly, because of all the different PCs out there, it is very hard to predict exactly how long the palette change takes.
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