Effect and Wind LOD are new concepts starting with SpeedTree® v6.0. In the same manner that SpeedTrees have always had geometry LOD, now it is very easy to set up shader effect LOD. Trees far away do not need all of the shader effects that are used on trees close to the camera. The SRT writer is also intelligent about using the effect setup for a particular tree/LOD to make the vertex buffers as small as possible to accomodate the needed effects. This feature dramatically improves both memory usage and rendering speed.
Effect LOD is set up pre-tree by pressing the property button “LOD:Effect LOD…” on a tree object. This will launch the Effect LOD dialog.
In the Effect LOD dialog, all of the materials for a tree are listed on the left. A material can be selected by clicking on it, and multiple materials can be selected at the same time. Once a material is selected, the effect LOD for that particular material is shown to the right on the sliders.
Each effect slider will display the number of LOD levels that are set up for the tree. The number of LODs in a tree is configured in the SpeedTree® Modeler. Each slider also has a number of movable points. These points indicate the transition from one effect LOD type to another. It should be noted that these points can be stacked on top of one another. For example, the ambient contrast effect can be computed per-pixel, per-vertex, or not at all. Placing both slider points at the same LOD transition would make the effect drop from per-pixel down to none.
A number of effect lod presets are available in the preset choicebox at the top of the dialog. On initial tree load, the effect sliders will be configured to the same as the “Standard” preset, which sets up a general falloff of shader effects, taking into account whether certain textures (such as detail and specular) are being used for a material.
To avoid popping of effects between LOD, the compilation process will intelligently mark effects as needing to be faded if the next LOD requires a different (or no) effect. When shaders are created, they will take this into account.
Wind LOD is very similar to Effect LOD, except that it is one slider for the whole tree, not per material. Wind effects vary from full branch and leaf wind, to just branch wind, to just global motion (including on billboards), and none. Billboards will pick up whatever wind effect is on the final LOD. They will be none if it is none, or they will be global for anything else.
The compilation process will set up the blending/falloff of wind effects between LODs similarly to the effects.