Draw a forest.

While working on our first title in MindLink Studio ("Telladar Chronicles: Decline"), we've set one very ambitious goal for that times: be able to show like 20K soldiers clashing on battlefields. With full 3D representation of everything. Back in 2002 we didn't seen anything like this yet.

I had an obvious idea of using sprites for lowest LODs to be able to draw such a large world. After few years of development and experimentation I've ended up with following solution.

When you need something to be drawn at distance, you ask sprites rendering subsystem to provide you with sprite representation of this. If something already in cache - you're done.

In opposite case subsystem considers size of the thing and selects place for it in sprites cache. This textures are divided on rows of predefined height and it selects one with best smallest row height. It injects sprite into the row, modifying row linked list. Rows contents is managed by subsystem like in any common memory manager. To wipe the row if it become too fragmented just copy it's content to another row, updating the sprites vertexes.

After getting sprite representation, LOD system injects four vertexes into dynamic storage. Great thing about this approach - you can fire-and-forget about your sprites. As long your sprite is alive - it will be rendered in batch with others. And you can just ignore updates for distant objects for any amount of frames (nobody ever will notice this on great distances).

To erase the sprite - ignore it when constructing your next ping-pong index buffer. To reuse the space in vertex buffer - make sure enough frames passed from the moment it was used last time.

In this way we were able to draw forests with hundreds of thousand of trees at real time, still providing nice 3D trees at close distance.

Soldiers was a bit tricky, as you need to animate them to look believable. After months of visual tests I've came to conclusion that you need to provide only 2-3 frames of walking animations to "shimmer" on distance.

Forest in action:

Lighting is a bit outdated. Still there is something like 30K trees in viewport with 30 FPS on SM1 hardware.