Is there any way to make a nice 3d plants based on alpha channel?

kurt_hectic

Hello,

Is there any way to make a nice 3d plants based on alpha channel?

At the moment I'm making some islands... with a lot of plants. The pain is that the player has a free cam and can aim the island from any direction. So I can't use simple planes with alpha channel. Of course I can't make it from polygons because of the limitations.

So, how to make it? To be honest, except SpeedTree and AAA games I've never seen a good looking plants based on alpha channel...


Bad examples:






And how it should looks like:






So I'm planing to make some weir spheres with alpha and attach to it even more alphas... damn, it's sounds like crazy plan but really I don't know how to create low poly, nice looking forest.

1)Could you give me some examples how it should be done?

2)I heard a lot about alpha channel; that it's tough for game engines. That I shouldn't put alpha on alpha ect. Could you provide me some more technical information how to use it and more important how many alphas I could put to the engine? I'll make tests to check the fps but more theoretical information could be useful.

Thx

Mark Dygert

1) It really depends on the engine and the specifics of the game.

Some general info that might be helpful:
http://www.polycount.com/forum/showthread.php?p=1520610#post1520610

Other general guidelines stuff:
Try to keep as few transparent pixels floating around as possible. Trim the opacity out of the planes, even if it means a few more polys if it takes out a lot of transparent pixels its normally worth it.

Try not stack them, it can cause slow down and display issues.
Try not to intersect transparent planes, cut them where they meet that way one object isn't behind and in front of the other one at the same time, this can cause some slow down and sorting issues.

kurt_hectic

Thanks man;)

I did a lot of these alpha action in the past...but never a huge forest.

Eric Chadwick

Here's some more tech info about alpha, and why it gets slow to render.
http://wiki.polycount.com/TransparencyMap

For rendering large forests of trees, often a game will use LODs and impostors
https://developer.valvesoftware.com/wiki/LOD_Models
http://www.terathon.com/wiki/index.php/Using_Impostors

bac9-flcl

That easy trick might be helpful too: http://simonschreibt.blogspot.de/2013/02/airborn-trees.html

kurt_hectic

Thanks for the links!
Impostors rox but are 2 complicated to create for a freelancer ...
ha! so there is more crazy guys like me ?

Eric Chadwick

Most game engines have LOD systems. For the lowest LOD just use a plane that always faces the camera; most engines also have that functionality. Which engine are you using?

Also, for a forest of many trees, you'll need to use Alpha Test instead of smooth alpha. See the Transparency Map link for info why.