3D models vs Sprites

Kilgore__Trout

Hi,

Coming fairly close to finishing first game and starting to think a little about a second. Used pre-rendered first time around, but based on the number of poses/weapon combinations, it would lead to vast sprite sheets, so not sure it’s going to be viable this time.

Any advice on deciding between sprites/pre-renderer vs models? Is there a significant increase in complexity?

Thanks

Darren Sweeney

If you have a variety of poses and weapons, why are they not separate instead of having a movement for every weapon? Models are for 3D and sprites 2D, unless you have a certain style were you use 2D sprites in a 3D world (Not UI or HUD) i'd have to see the game. Not sure what you are asking.

Kilgore__Trout

I'm using images captured from a 3d model, organised into sprite sheets, and drawn onto a plane for the characters of my first game. Perspective is top down 2D. Am considering whether to keep doing this, or to use actual models for next game. Using Unity.

Basically, I'm asking for opinions on the pros/cons of using pre-rendered 3d vs actual 3d models. Stuff like when one is better than the other, perfomance, memory usage. The point I was trying to make, was that characters who perform a lot of different actions, and who carry different weapons may necessitate large sprite sheets if pre-rendered.

I see what you mean about splitting the animations, like one walk cycle, one crouch animation, and then drawing the upper body with the various weapons on top.

Darren Sweeney

Never hard of anyone doing that, people who use sprites just draw them digitally.

The Advantage of using pre-rendered it that complex models pre-rendered will be less computationally intense that rendered models in run time. If you are using captured images of 3D models then it is less intense.

The Disadvantage of using pre-rendered is that it's less interactive since it's a static model. But you are capturing frames of a model and making a sprite sheet so it shouldn't matter.

I'd go with 3D models if you are using unity because it's not like it will make a performance issue. It depends on if you are able to animate the character.

satchmo

You're describing 'impostors' - 3d renders cached as 2d images, either as a preprocess or at runtime, and rendered in-game as camera-facing quads. The most common use for impostors is rendering large amounts of objects whose vertex transformation cost might otherwise be too expensive, and doing so with only a handful of draw calls. The downsides are decreased fillrate (there's usually a non-trivial amount of empty space in each quad and overdraw will almost certainly be higher) and the increased memory usage required to store the sheets - especially if you have multiple frames of animation. Another sizable downside is the pipeline overhead; you also have to take into account the extra work it takes set up the baking process in the first place, update them if the asset changes, and do proper texture packing & unpacking (to avoid wasted space) and calculate the resulting UVs.

There are extensions to the technique for improving their visual quality, such as also baking normal maps for real-time lighting and depth maps to do some raycasting for proper occlusion, but these just add to the fillrate problem which is probably already a bottleneck.

Without knowing your game it's hard to say, but I'd guess it's almost definitely not worth it. Unless you have a good reason that you have to use impostors, all you'll be doing is adding all the above overhead for not much gain (or even a loss if you're on a platform that has limited fillrate and/or framebuffer bandwidth). You'll also be restricting the framerate of your animations quite a lot to avoid using a crazy amount of memory, as well as introducing other restrictions such as the weapon problem mentioned above. You're much better off keeping your models as 3D, and just making sure they have a reasonable number of well-tuned LODs.

Kilgore__Trout

Thanks, lots to think about here. Imposters might be used in Alan Wake for some of the vegetation. Maybe was being paranoid, but some shrubs seemed to be rotating to follow me when moving.

It's still up in the air, but I'd really like to make a TBS with some shared ground with the combat in the ufo games, shadowrun, jagged alliance etc. My first attempt was along these lines, but I didn't understand enough of the basics to complete it. Maybe it will go better this time.

satchmo

Technically an impostor is a 3d render, as opposed to a texture painted by an artist. They're both rendered at runtime on billboards that usually always face the camera.

But you're right, alpha-tested billboards are a very common way to do vegetation, as building even a simple tree with geometry would result in a very heavy mesh. Almost every game does vegetation this way to varying degrees - for LODs at a distance, or for the complex parts of the vegetation up close (eg., a tree would have a mesh trunk, but the branches would be made up by a handful of billboarded sprites). It can be subtle when done well, but is always obvious if you're looking for it.