Chapter 5. Bring Me a Shrubbery

Vegetation has a huge impact on scene quality. Significant coverage was once difficult to achieve without making compromises for memory and rendering power. Early computer games would use single pixels to sell the impression of movement (and sometimes even that was a stretch). Thanks to current Graphics Processing Unit (GPU) technology it's realistic to have lush scenes consisting of 2,50,000 vegetation objects on mid-range gaming PCs.

GROME, Unity, and other game engines all have their own unique vegetation system but broadly speaking they do the same thing; take a single object (such as a tree or grass billboard) and draw thousands of copies at different locations within the scene.

Games commonly use smoke and mirror techniques to fool the eye into thinking a scene is more complex than it is, even using old cinema tricks like forced perspective. The amount of detail we want to include is impacted by the altitude of the camera in our game; a flying game would...

Exportability of vegetation

Vegetation data does not translate well to Unity and UDK, there's no easy way to move it unless they are using GROME's native Graphite engine (such as the Ogre3D Graphite rendering module).

The most practical method of transferring vegetation coverage to Unity and UDK is through the use of coverage masks. GROME uses masks to populate vegetation within zones and these are saved as image files by several of the built-in exporters.

These masks can (with some effort) be imported into Unity and UDK but this presents practical editing issues should we need to perform any fine-tuning to the game map. Once a bulk transfer of vegetation data has been completed, any edits later on become more difficult to integrate, especially if it's required to reimport everything, potentially losing many hours of work. For this reason I usually recommend using Unity or UDKs built-in vegetation tools from this point onward but there are no hard-and-fast rules.

GROME detail objects and billboards

GROME's vegetation layers have a set of properties controlling visibility range, fade-out distance, and create objects where one model is swapped for a lower detail one (Level of Detail "LOD" collections). It also supports billboards; a term used in computer graphics to describe a textured quad that always faces the camera. A billboard quad is aligned to the camera using a vertex shader on the 3D hardware and can process thousands of billboards very quickly. Most game engines support this kind of object.

GROME vegetation layers are named "Detail" layers since it can render any kind of object such as rocks or debris, not just vegetation.

GROME also divides detail layers into two very distinct types:

• 3D Objects

• Billboards

You specify the type of detail layer when assigning zones to a Detail layer. Again these types won't export directly to our game engines.

The Detail layer stack

To set the mode of the layer stack to Details we set it from the drop-down control...

Summary

We looked at the detail layer stack and the two types of detail layers (Grass Billboards and 3D Objects). We went through each tool available to Detail layers; brushes, importing, and procedural mapping using distribution masks. Finally, we had a quick look at blending and the issue of baking shadows from trees onto terrain using object layers.

In the next chapter, we look at adding water features such as rivers, water planes, and a look at road building.