How'd they do it: sphere effects in Osmos

Question

I'm curious how the sphere effects were done in Osmos from Hemisphere Games. Any ideas how the resolution independent zoom in was achieved?

Edit, more specifics on questions:

1. How do you render the spheres so they look good at full zoom out, and full zoom in?
2. How would one make the nice particle effects in 100's of spheres all at once?
3. How to construct your scene/spheres so the big spheres look round even at full zoom?

Gameplay video

Hemisphere Games

Answer 1

Daniel, I have this game and I was wondering the same thing myself when I first played it. It's quite impressive. I don't know for sure, but I think for the spheres, they're using a series of overlapping translucent rotating bitmaps to give the illusion of particles within the spheres. This is very efficient in OpenGL. They would be rather large in source (probably twice the largest size you see on-screen) and then down-sampled as textures on-the-fly during rendering. This would also solve the problem of appearing round at any size, since it avoids using a finite polygon. Whether or not this is the technique used in Osmos, it's something you might want to give a try...

Answer 2

1 and 3: It's all pretty basic functionality of a modern graphics chip, there is a pixel sampling method which ensures that things look smooth even though an image is rendered in non-native resolution. You just have to make sure that the image is of reasonable size for the big spheres not to become blurry.

The common method is to use a 3D api for invoking this, even though your game is 2D. Often you'd use a piece of middleware that translates 2D commands into 3D equivalents.

I don't know how it specifically works on the iPhone, but it's certainly nothing out of the ordinary so there should be plenty material covering the topic.

2: I don't see a lot of particle effects in that video, there is a few particles of exhaust, but they don't need to be implemented in a different manner than the spheres.