I am working on a cocoa(Mac OS X) opengl game. The game is a rotatable overhead 45 degree downlooking angle, so you can rotate on the X axis look down at the center of the screen. I was having some issues determing what kind of images to use. I could import full 3d models and take a hit to the game speed which i would like to avoid. Or i could use sprites and display the apporatie image as per the camara angle but this would take a hit to the 3d realism. Any input from you guys i really cant make up my mind, maybe im missing more options and so-forth. Thanks!

Sprites wouldn't hit the 3D realism that much. As long as you make it believable (good sprites, smooth transition), then your users shouldn't really care.

Another approach, taken by many games, is a hybrid approach, rendering the backround, terrain, etc. with sprites and the characters etc. with 3D models. SimCity uses this (models for terrain, animated buildings, sprites for static buildings), as well as some other games (LionHeart used models for characters and sprites for everything else).

What kind of game are you making? RTS? It depends somewhat on what kind of game you're making.

Well i was going for a Massive Online Role Playing game, so there will be a lot of images on the screen, which is why im concerned about this. Im working on the Myth The Fallen Lords kinda graphics system. So i would have height maps for terrian rendered with texture. Im thinking about using Cubes with textures for most static images. But the players and the other moving "living" things in the game i need some ideas for. Thanks

MMORPG? How long have you been in the game industry anyways? Or do you have 100 people working behind you?

Does the game allow only rotation to the -45, 0, and 45 degrees, or does the camera 'smoothly' rotate between the angles?

Ive been in the gaming industry for about 5 years now and have worked on 3 MMORPG, im just working on the engine right now so i havent brought on a team yet, and this is my first time working with OpenGL for a big project. Camara smoothly rotates around the axis. Imagine a ring above the center of the screen the camara will rotate around it always facing the center looking down at a 45 degree angle, which will make it harder to use sprites with the amount of possible angles unless i wanted them to jump to 8 or 16 facing angles which would still not be fluid. The other MMORPG have been 2d sprite based. This time i wanted to use the built in effects and the likes of OpenGL. Thanks Again

If the camera rotates very quickly (and snaps to several different angles) you can get away with sprites. If it rotates smoothly (slowly) but snaps to several different angles, then you can render sprites when the camera is stationary and low-poly models when it is moving. Some optimizations you could make to increase the speed is to update the models on the sides of the screen less frequently, or to use some kind of advanced graphics engine and only update what needs to be updated.

Are you assuming that your customers won't have hardware acceleration, or do you just want to squeeze the most speed out of your game? Many (Windows) MMORPGs are full 3D, super high detail level. I'm not that familiar with Macs, so fill me in.

Hope this helps, good luck!

Macs are a little behind the PC world as far as 3d and i dont want to limit my game to the most advanced system out there, 32 or 64 MB video Memory will be the target area. As far as the graphics on macs most people accept less detailed games as the norm so something like WoW, Shadowbane, Everquest is beyond my projected scope as far as graphics. Im aiming towards something more Diablo 1 or Myth The Fallen lords kinda graphics. If i use sprites and models together that will increase the hard drive size requirements, but i havent played around with model loading too much yet as far as how much processor power it will require.
Camara rotation speeds will depending on the user input, the user can rotate fast or slow depending on how much input he/she gives to the mouse or other input device so i want to assure the best picture possible.
As far as mixing sprites and models that is an interesting idea and i havent come accross it myself, i have been trying to figure out what other game makers have done in the past and work with the ideas that they have come up with.

Sprites and models together won't take up much disk space (sprites shouldn't at all, if you're using some kind of compressed format (not JPEG) ). 32-64 MB is quite enough for you to put in a fairly good number of polys. Ever played WarCraft III? Runs (at ~25 FPS) on systems with 4 MB of video memory. 100% models. This shows that, even if you do use lots of models, as long as your structure and optimize correctly (octrees, BSP trees, ...), you shouldn't have a problem getting your game to run at an acceptable framerate. Unless your game is highly-action based, framerate won't be much of a problem.

Hard drive space is at a premium, and if you use things like gzip, then you can use even less space.

Sprites and models have been mixed for many years. Billboarding, particles, ... are the most obvious, but like I mentioned, SimCity uses a mix of 3D terrain, and 2D/3D buildings (plus a graphics engine that keeps track of what needs to be updated and updates only those objects), and some games also use a '3D in 2D' approach, where you have a pre-rendered background, with 3D models on top of that.

If you finish your game, I would love to see a PC port :).