Some of objects on the background can be visually "closer" to user than 3D model, that is part of the 3D model is "behind" that object and that part must not be drawn. "Few games use scenes consisting of 3D models moving over 2D background. I already described the problem hereand here, so I cite myself: For LLE we still need somehow resize buffer texture. Unfortunately, it works only for HLE, because BgCopy is high-level command. I used that hack in Glide64 and I still don't know better solution. It is no problem to create 512x287 texture and render it to frame buffer.
Why it is a problem for hardware graphics plugin? The plugin executes BgCopy command, which loads 512x287 image. Now buffer has correct proportions, and 3D models can be rendered over. In fact BgCopy works as memcpy to copy background content from one address in RDRAM to another. When buffer copy completed, the game allocates buffer with the same origin, but with width 448. The game allocates color buffer with width 512 and renders background with BgCopy command into it. To optimize background load and rendering on N64 hardware, background loaded as image with width 512. The first problem, which hardware plugin faces in this game is the way how background loaded to frame buffer. Video interface stretches image to TV resolution 640x480. Frame buffer size corresponds to background size. Background size may vary from place to place: someplace it is 436x384, someplace 448x328 and so on. What makes the game hard to emulate? As you know, the game consists of static 2D backgrounds with 3D models moving over. Later necessary functionality was added to glide wrapper, so you can run the game on any modern PC card. Abilities of 3dfx graphics card allowed me to obtain pretty good result: the game was fully playable on Voodoo4/5 with some minor glitches. I spent lots of time on this game when I worked on Glide64 plugin. While the game uses standard ucode (or slight modification of standard one), it uses few non-standard tricks, which are hard to reproduce on PC hardware. Resident Evil 2 for Nintendo 64 is hard to emulate game.
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