This article was updated. Jump to Update 1. Update 2.
Today, a tree from The Elder Scrolls: Oblivion and a palm tree from Enemy Territory: Quake Wars will compete for us! This article is about how vegetation can be optimized to be able to show many (palm)trees in a level.
Round #1 – Optimization
In the distance, both games use one simple billboard (and a texture) to display the (palm)tree. This saves many polygons.
Enemy Territory has the great “set r_skipdiffuse 1” command, which let you deactivate the diffuse texture to see only the geometry (in black color). In Oblivion, on the other hand, you can turn the “Tree Fade” slider to “0” which makes you see only billboard trees. Both options are great to visualize the difference between the fully detailed version and the simple billboard for the distance.
1 Point for both of them, as they are both very optimized!1:1
Round #2 – LOD Blending
For the next round, the opponents have to answer the question:
The answer is: YES! Both blend between their detailed version and the simple billboard. Instead if “just” doing a hard switching, they use a “grainy blend” to hide the transition (it’s called “Dithering”, we already saw it in my article about Assassin’s Creed LOD blending).
If you look carefully, you’ll see that they first blend in the detail geometry and then fade out the sprite while you approach them. If you depart, the sprite fades in first and then the geometry fades out. With that, they avoid showing a 50% transparent tree/palm when geometry and sprite are both fade in/out and “meet” at 50% fading progress.
There’s a light *plop* on the palm tree, but this nice, careful timing of the fading gets a shiny point for both of them!
2:2
Round #3 – Variation
When it comes to variation, the games use a different approach.
Enemy Territory offers variation in the sense that they store several sprites of their palm tree captured from different directions. Depending on your relative viewing direction to the palm tree, they pick a different sprite. So, if you circle around it, you’ll see the palm tree changing shape even thought it’s just a billboard (this is called an “imposter”)!
This is what the palm tree texture looks like: The same palm tree but captured from 12 different directions:
It’s interesting that they packed the Diffuse & Normal Map together in one texture.
While Oblivion does not swap the sprite depending on the viewing angle, the game does offer different tree types (where there is only one type of palm tree shown in Enemy Territory).
I combined all the different tree sprites from Oblivion into this wonderful collage below.
So, where Oblivion offers more variation, Enemy Territory offers more flexibility! I would say, it’s fair to give both a point.3:3
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Update 1Update 2
I feel like the palm should LOSE a point for changing angles! It’s a neat idea when you’re staring straight at it, but if you’re looking at something else, which are you going to notice more — that a round-ish mass in the distance isn’t varying its silhouette like it should be, or that something with a pointy distinct shape just suddenly jumped? A correcting discontinuity draws your attention way more than an incorrect continuity, I think…. that was the whole point of Round 2, no? ;)
You’re right. OR it could be, that they not ONLY blend sprite –> geometry but also sprite –> sprite. This would also avoid the *plopp* :D
Could have been way better if the scores corresponded with the trees on the right side. Palm on the left in the pics but on the right in the scoring? Beyond confusing!
I changed the article :) Thank you for the suggestion! Is it better now? (actually i only had to change the 2:3 to 3:2)
Overgrowth, the upcoming indie game of Wolfire, also make a great use of impostors.
They have a detailed article about them, and all the visual trickery they use !
http://blog.wolfire.com/2010/10/Imposters
Thank you very much for handing out this link! Actually it was already mentioned and i added it in the “Update” area of the article at the end. But maybe i should add the link to the text too…to make sure that people see it. :)