: I'd like to know why we can't have hi-res sprites, wouldn't it be easier than
: making everything 3D? And I think a fully 3D AO would render old machines
: unable to play Marathon.
If you have an older machine, you might have noticed a slight (or not so slight) delay in gameplay every time an new texture must be loaded. Typically, what you'll observe is that a door that is opening stops for a brief moment before opening the rest of the way. Some levels (eg. Acme Station) are virtually unplayable using high-res textures and OpenGL on older machines due to the inherent lag, which is usually sufficent for the Pfhor to kill the player while they wait for the textures to load and to regain control of the marine. Now imagine having to load a high-resolution animated sprite for a monster or a weapon, and to do so for all monsters in view. Unless you have a really high-end graphics card, you would quickly run out of room for all the animated sprites and would have to continuously reload them - it would totally wreck the game.
With 3D models, rendering and animation is done entirely in hardware in OpenGL. Because the models are expressed in terms of the geometry using mathematical relationships, the memory requirements are actually quite small. Assuming the number of polys in each model is kept relatively small, most graphics cards will be able to handle rendering in real-time. In addition, modern software for 3D rendering actually makes the process of generating animated 3D models musch simpler than working with animated sprites. The develoment time for 3D models is thus much shorter than for high-res sprites.
In terms of playability on older machines - I hear you! The beauty of the AO engine is that as long as scenario makers include the traditional format shapes file, you will always be able to play Marathon on older hardware, minus the OpenGL effects.
