4 . 11. Trees and Vegetation

4.11. TREES AND VEGETATIONRendering of trees and vegetation

VEGETATIONRendering flora

Video not available in on-line slides

Grass

Grass is typically rendered using (randomly) placed intersecting quads which are texture mapped and rendered with an alpha test.

The grass quad are crossed (using a star-like configuration) to ensure good visual quality independent of the line of sight.

GrassDifferent alpha/depth tests can be used at runtime to suitably render a clump of grass quads and provide the appearance of densely packed grass.

Grass

In a vertex shader the top two vertices of each quad can be animated (using a combination of sinusoidal waves) to provide a natural looking wave modelled motion due to wind effects.

By having separate animation parameters for each cluster or clump of grass, more chaotic (i.e. natural) behaviour can be introduced.

GrassWhen lighting the grass, the quad’s normal may also be updated to reflect the grass movement.

Alternatively, the colour change can be simulated by directly modifying the rendered colour based on the oscillations.

TREESRendering trees

Video not available in on-line slides

Trees

At a distance, a tree can be adequately rendered using a billboard or imposter.

Up close, trees are typically separated into two different parts: •solid component of the tree (trunk and branches)•foliage or leaves.

The trunk and the branches are represented using a triangle mesh. Leaves are represented using an image of a leaf group textured using a quad.

Minor branches can be

approximated by simple

polygon strips

Leaves are rendered as

texture mapped quads

More sophisticat

ed tree rendering deals with issues such

as silhouette clipping

Or accurate

leaf shadowing /

lighting

DIRECTED READINGDirected reading regarding trees and vegetation

Directed

reading

Directed reading: Directed

reading

• Read GPU Gems - Rendering Countless Blades of Waving Grass – for coverage of how to render grass• Read Creation and

Rendering of Realistic Trees – for an early paper on generating trees• Read GPU Gems 3 - Next-

Generation SpeedTree Rendering – for an exploration of current tree rendering approaches

Summary

To do:Read the directed

readingThink if you would like

to implement either approach within your project

Today we explored:

Overview of vegetation rendering

Overview of tree rendering