Okay I'm pretty new to 3D, as well as OpenGL, but not to programming. My goal is to develop a 2D/3D engine along the lines of Strider 2. All the sprites are set to be 2D billboards and the actual levels are 3D models. The camera angle is always centered about the player in 2D and the level rotates when necessary to simulate walking around corners etc. My question is how difficult would it be to have the 2D billboards interact with their 3D surroundings? I'd like to know up front if I'm getting in over my head. Any references/tutorials on this subject would be appreciated. Thank you. [edited by - Xorcist on November 6, 2002 5:32:33 AM]

Very good idea... its not so hard to implement. but what do you mean by interaction. you mean collision with the 3d map? or just rotation/movement?

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DaHeR.RailgunMaster

Well both actually.

I''m sure I''d have to setup some sort of "pathway" that the sprites would follow and based on their postion on that path, rotate the map left or right to simulate turns etc. Not quite sure how I''d go about laying that path out though. Note that I plan to treat the sprites as if they where in a completely 2D environment with movement options of up, down, left, and right only.

Collision with the map itself is also something I was worried about. Like I said I''m kinda new to 3D (just finished reading OpenGL Game Programming, and started working with some of the NeHe tutorials). I heard collision in 3D isn''t the easiest thing to do, and wondered how I might go about making sure my 2D sprites actually stay on the map.

At this point I''m just going to take it a step at a time, but I want to make sure those steps are at least in the right direction.


P.S. If there any any programmers interested in helping out on this project, I''m sure I could use it, so feel free to ask.

I don''t think it is a good idea to have 2d sprites in a 3d world, it looks crappy. The only 2D things that look decent are some plants (small plants), and maybe very small projectiles. Anything else looks ugly. But, of course, it is more simple and faster to do a colision detection between a plane and a 3d world, than between a 3d world and a 3d object...

Exactly how large could a sprite be in OpenGL, before I started to see a big dropoff in frame rate? I''ve heard there are some limitations on texture sizes (64x64)? I assume larger sprites would need to be broken into multiple billboards and aligned. Also what would be the fastest way to do animation? I''ve heard using the framebuffer is a bad idea, but animated textures seem to work fine, is this true?

There''s a limit on how small it is, which I believe is 64x64 as you said. And I think you have to keep it in a multiple of 2 (64,128..etc).

Smallest is 1x1. Voodoo 3 and earlier have a max size of 256x256, and some earlier cards will be upset by non-square texture sizes. Unless you use extensions then they should be power of 2 in size. Newer cards have insanly large max texture sizes, I seem to remember there being a way to find out at runtime somehow..

That''s not a bad idea otherwise, game coders from Creative Assembly (Shogun Total War, Medieval Total War) won''t have done their units with sprites.

But I think it makes sense only if you plan to have a huge number of units on your map ...

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